diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3efcfa0e9..b575cc6bb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,32 @@
 # Changelog
 
+## Unreleased
+
+### Candid
+
+* [BREAKING]: type representation was optimized to improve performance:
+  + In `Type::Var(var)` `var` now has type `TypeKey` instead of `String`. Calling `var.as_str()` returns `&str` and `var.to_string()` returns a `String`. The string representation of indexed variables remains `table{index}` to maintain compatibility with previous versions.
+  + `TypeEnv` now contains a `HashMap` instead of `BTreeMap`. Code that relied on the iteration order of the map (e.g. `env.0.iter()`) should make use of the newly added `TypeEnv::to_sorted_iter()` method which returns types sorted by their keys.
+  + The `args` and `rets` fields of the `candid::types::internal::Function` struct now are a `Vec<ArgType>` instead of `Vec<Type>`, to preserve names.
+  + The `TypeInner::Class` variant now takes `Vec<ArgType>` instead of `Vec<Type>` as its first parameter, to preserve argument names.
+
+* [BREAKING]: Removed the `candid::pretty::concat` function
+  + `candid::pretty::enclose` and `candid::pretty:enclose_space` don't collapse the separators on empty documents anymore
+
+* Non-breaking changes:
+  + Added `pp_named_args`, `pp_named_init_args` in `pretty::candid` module.
+  + The `JavaScript` `didc` target now exports its generated IDL type objects.
+  + The `JavaScript` and `TypeScript` `didc` targets now export `idlService` and `idlInitArgs` (non-factory-function alternatives to `idlFactory` and `init`).
+
+### candid_parser
+
+* Breaking changes:
+  + The `args` field in both `FuncType` and `IDLInitArgs` now have type `Vec<IDLArgType>`.
+  + The `rets` field in `FuncType` now has type `Vec<IDLArgType>`.
+
+* Non-breaking changes:
+  + Supports parsing the arguments' names for `func` and `service` (init args).
+
 ## 2026-05-27
 
 ### Candid 0.10.29
@@ -539,7 +566,7 @@ The source code of this tool has been removed, as it was deprecated in [PR#405](
 * Bump ic-types to 0.3
 * `candid::utils::service_compatible` to check for upgrade compatibility of two service types
 
-## 2021-12-20 
+## 2021-12-20
 
 ### Rust (0.7.9)
 
@@ -565,7 +592,7 @@ The source code of this tool has been removed, as it was deprecated in [PR#405](
 
 ### Rust (0.7.5 -- 0.7.7)
 
-* Support import when parsing did files with `check_file` function 
+* Support import when parsing did files with `check_file` function
 * Fix TypeScript binding for reference types
 
 ### Candid UI
@@ -584,7 +611,7 @@ The source code of this tool has been removed, as it was deprecated in [PR#405](
 * Add `#[candid_path("path_to_candid")]` helper attribute to the candid derive macro
 * Update `ic-types` to 0.2.0
 
-## 2021-06-03 
+## 2021-06-03
 
 ### Spec
 
@@ -624,7 +651,7 @@ The source code of this tool has been removed, as it was deprecated in [PR#405](
 * Fix TypeScript binding for tuple
 * Rust support for Func and Service value
 
-## 2021-03-17 
+## 2021-03-17
 
 ### Rust (0.6.18)
 
@@ -775,7 +802,7 @@ The source code of this tool has been removed, as it was deprecated in [PR#405](
 
 * No longer requires the shortest LEB128 number in deserialization [#79](https://github.com/dfinity/candid/pull/79)
 
-### Rust 
+### Rust
 
 * Parser improvements:
   + Floats in fractional number, no e-notation yet
diff --git a/Cargo.lock b/Cargo.lock
index 2529594e2..52b23c12d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -11,6 +11,12 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "allocator-api2"
+version = "0.2.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683d7910e743518b0e34f1186f92494becacb047c7b6bf616c96772180fef923"
+
 [[package]]
 name = "anstream"
 version = "0.6.15"
@@ -217,6 +223,8 @@ dependencies = [
  "byteorder",
  "candid_derive 0.10.29",
  "candid_parser 0.3.2",
+ "foldhash",
+ "hashbrown 0.15.5",
  "hex",
  "ic_principal 0.1.3",
  "leb128",
@@ -613,6 +621,12 @@ version = "1.0.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3f9eec918d3f24069decb9af1554cad7c880e2da24a9afd88aca000531ab82c1"
 
+[[package]]
+name = "foldhash"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9c4f5dac5e15c24eb999c26181a6ca40b39fe946cbe4c263c7209467bc83af2"
+
 [[package]]
 name = "generic-array"
 version = "0.14.7"
@@ -680,6 +694,17 @@ version = "0.14.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e5274423e17b7c9fc20b6e7e208532f9b19825d82dfd615708b70edd83df41f1"
 
+[[package]]
+name = "hashbrown"
+version = "0.15.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9229cfe53dfd69f0609a49f65461bd93001ea1ef889cd5529dd176593f5338a1"
+dependencies = [
+ "allocator-api2",
+ "equivalent",
+ "foldhash",
+]
+
 [[package]]
 name = "heck"
 version = "0.5.0"
@@ -737,7 +762,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "168fb715dda47215e360912c096649d23d58bf392ac62f73919e831745e40f26"
 dependencies = [
  "equivalent",
- "hashbrown",
+ "hashbrown 0.14.5",
 ]
 
 [[package]]
diff --git a/clippy.toml b/clippy.toml
new file mode 100644
index 000000000..db551b3a9
--- /dev/null
+++ b/clippy.toml
@@ -0,0 +1 @@
+ignore-interior-mutability = ["candid::types::type_key::TypeKey"]
diff --git a/rust/bench/Cargo.lock b/rust/bench/Cargo.lock
index cd34cf046..d6b0fc946 100644
--- a/rust/bench/Cargo.lock
+++ b/rust/bench/Cargo.lock
@@ -11,6 +11,12 @@ dependencies = [
  "memchr",
 ]
 
+[[package]]
+name = "allocator-api2"
+version = "0.2.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683d7910e743518b0e34f1186f92494becacb047c7b6bf616c96772180fef923"
+
 [[package]]
 name = "anyhow"
 version = "1.0.100"
@@ -162,6 +168,8 @@ dependencies = [
  "binread",
  "byteorder",
  "candid_derive",
+ "foldhash",
+ "hashbrown 0.15.5",
  "hex",
  "ic_principal",
  "leb128",
@@ -416,6 +424,12 @@ version = "1.0.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3f9eec918d3f24069decb9af1554cad7c880e2da24a9afd88aca000531ab82c1"
 
+[[package]]
+name = "foldhash"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9c4f5dac5e15c24eb999c26181a6ca40b39fe946cbe4c263c7209467bc83af2"
+
 [[package]]
 name = "generic-array"
 version = "0.14.7"
@@ -453,6 +467,17 @@ dependencies = [
  "thiserror 2.0.18",
 ]
 
+[[package]]
+name = "hashbrown"
+version = "0.15.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9229cfe53dfd69f0609a49f65461bd93001ea1ef889cd5529dd176593f5338a1"
+dependencies = [
+ "allocator-api2",
+ "equivalent",
+ "foldhash",
+]
+
 [[package]]
 name = "hashbrown"
 version = "0.16.1"
@@ -530,7 +555,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7714e70437a7dc3ac8eb7e6f8df75fd8eb422675fc7678aff7364301092b1017"
 dependencies = [
  "equivalent",
- "hashbrown",
+ "hashbrown 0.16.1",
 ]
 
 [[package]]
diff --git a/rust/bench/bench.rs b/rust/bench/bench.rs
index 7dd94f413..5aeb941c2 100644
--- a/rust/bench/bench.rs
+++ b/rust/bench/bench.rs
@@ -269,10 +269,15 @@ fn nns() -> BenchResult {
         let args = candid_parser::parse_idl_args(motion_proposal).unwrap();
         let serv = serv.unwrap();
         let method = &env.get_method(&serv, "manage_neuron").unwrap();
+        let arg_tys = method
+            .args
+            .iter()
+            .map(|arg| arg.typ.clone())
+            .collect::<Vec<_>>();
         drop(_p);
         let bytes = {
             let _p = bench_scope("1. Encoding");
-            args.to_bytes_with_types(&env, &method.args).unwrap()
+            args.to_bytes_with_types(&env, &arg_tys).unwrap()
         };
         {
             let _p = bench_scope("2. Decoding");
@@ -514,15 +519,21 @@ fn subtype_decode() -> BenchResult {
 // code path. See https://github.com/dfinity/candid/issues/603
 #[bench(raw)]
 fn vec_service() -> BenchResult {
-    use candid::types::{Function, TypeEnv, TypeInner};
+    use candid::types::{ArgType, Function, TypeEnv, TypeInner};
 
     let mut config = DecoderConfig::new();
     config.set_decoding_quota(COST);
 
     let method_type: candid::types::Type = TypeInner::Func(Function {
         modes: vec![],
-        args: vec![TypeInner::Text.into()],
-        rets: vec![TypeInner::Nat64.into()],
+        args: vec![ArgType {
+            name: None,
+            typ: TypeInner::Text.into(),
+        }],
+        rets: vec![ArgType {
+            name: None,
+            typ: TypeInner::Nat64.into(),
+        }],
     })
     .into();
 
diff --git a/rust/candid/Cargo.toml b/rust/candid/Cargo.toml
index f46667c74..038a5eace 100644
--- a/rust/candid/Cargo.toml
+++ b/rust/candid/Cargo.toml
@@ -20,6 +20,8 @@ candid_derive = { path = "../candid_derive", version = "=0.10.29" }
 ic_principal = { path = "../ic_principal", version = "0.1.0" }
 binread = { version = "2.2", features = ["debug_template"] }
 byteorder = "1.5.0"
+foldhash = "0.1.3"
+hashbrown = "0.15"
 leb128 = "0.2.5"
 paste = "1.0"
 hex.workspace = true
diff --git a/rust/candid/fuzz/Cargo.lock b/rust/candid/fuzz/Cargo.lock
index c046c15f3..69cc5fbaf 100644
--- a/rust/candid/fuzz/Cargo.lock
+++ b/rust/candid/fuzz/Cargo.lock
@@ -2,6 +2,12 @@
 # It is not intended for manual editing.
 version = 4
 
+[[package]]
+name = "allocator-api2"
+version = "0.2.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "683d7910e743518b0e34f1186f92494becacb047c7b6bf616c96772180fef923"
+
 [[package]]
 name = "anyhow"
 version = "1.0.86"
@@ -66,12 +72,14 @@ checksum = "1fd0f2584146f6f2ef48085050886acf353beff7305ebd1ae69500e27c67f64b"
 
 [[package]]
 name = "candid"
-version = "0.10.27"
+version = "0.10.29"
 dependencies = [
  "anyhow",
  "binread",
  "byteorder",
  "candid_derive",
+ "foldhash",
+ "hashbrown",
  "hex",
  "ic_principal",
  "leb128",
@@ -97,7 +105,7 @@ dependencies = [
 
 [[package]]
 name = "candid_derive"
-version = "0.10.27"
+version = "0.10.29"
 dependencies = [
  "lazy_static",
  "proc-macro2",
@@ -172,6 +180,18 @@ version = "1.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3dca9240753cf90908d7e4aac30f630662b02aebaa1b58a3cadabdb23385b58b"
 
+[[package]]
+name = "equivalent"
+version = "1.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "877a4ace8713b0bcf2a4e7eec82529c029f1d0619886d18145fea96c3ffe5c0f"
+
+[[package]]
+name = "foldhash"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9c4f5dac5e15c24eb999c26181a6ca40b39fe946cbe4c263c7209467bc83af2"
+
 [[package]]
 name = "generic-array"
 version = "0.14.7"
@@ -182,6 +202,17 @@ dependencies = [
  "version_check",
 ]
 
+[[package]]
+name = "hashbrown"
+version = "0.15.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9229cfe53dfd69f0609a49f65461bd93001ea1ef889cd5529dd176593f5338a1"
+dependencies = [
+ "allocator-api2",
+ "equivalent",
+ "foldhash",
+]
+
 [[package]]
 name = "hex"
 version = "0.4.3"
diff --git a/rust/candid/src/binary_parser.rs b/rust/candid/src/binary_parser.rs
index 5a0bd2e4b..545701161 100644
--- a/rust/candid/src/binary_parser.rs
+++ b/rust/candid/src/binary_parser.rs
@@ -1,4 +1,5 @@
-use crate::types::internal::{Field, Function, Label, Type, TypeInner};
+use crate::types::internal::{ArgType, Field, Function, Label, Type, TypeInner, TypeKey};
+use crate::types::type_env::TypeMap;
 use crate::types::{FuncMode, TypeEnv};
 use anyhow::{anyhow, Context, Result};
 use binread::io::{Read, Seek};
@@ -142,9 +143,6 @@ pub struct PrincipalBytes {
     pub inner: Vec<u8>,
 }
 
-fn index_to_var(ind: i64) -> String {
-    format!("table{ind}")
-}
 impl IndexType {
     fn to_type(&self, len: u64) -> Result<Type> {
         Ok(match self.index {
@@ -152,7 +150,7 @@ impl IndexType {
                 if v >= len as i64 {
                     return Err(anyhow!("type index {} out of range", v));
                 }
-                TypeInner::Var(index_to_var(v))
+                TypeInner::Var(TypeKey::indexed(v))
             }
             -1 => TypeInner::Null,
             -2 => TypeInner::Bool,
@@ -208,10 +206,16 @@ impl ConsType {
                 let mut args = Vec::new();
                 let mut rets = Vec::new();
                 for arg in &f.args {
-                    args.push(arg.to_type(len)?);
+                    args.push(ArgType {
+                        name: None,
+                        typ: arg.to_type(len)?,
+                    });
                 }
                 for ret in &f.rets {
-                    rets.push(ret.to_type(len)?);
+                    rets.push(ArgType {
+                        name: None,
+                        typ: ret.to_type(len)?,
+                    });
                 }
                 TypeInner::Func(Function {
                     modes: f.ann.iter().map(|x| x.inner.clone()).collect(),
@@ -240,13 +244,12 @@ impl ConsType {
 }
 impl Table {
     fn to_env(&self, len: u64) -> Result<TypeEnv> {
-        use std::collections::BTreeMap;
-        let mut env = BTreeMap::new();
+        let mut env = TypeMap::default();
         for (i, t) in self.table.iter().enumerate() {
             let ty = t
                 .to_type(len)
                 .with_context(|| format!("Invalid table entry {i}: {t:?}"))?;
-            env.insert(index_to_var(i as i64), ty);
+            env.insert(TypeKey::indexed(i as i64), ty);
         }
         // validate method has func type
         for t in env.values() {
diff --git a/rust/candid/src/lib.rs b/rust/candid/src/lib.rs
index 75ca3c057..57e38781a 100644
--- a/rust/candid/src/lib.rs
+++ b/rust/candid/src/lib.rs
@@ -303,7 +303,7 @@ pub mod pretty;
 
 // Candid hash function comes from
 // https://caml.inria.fr/pub/papers/garrigue-polymorphic_variants-ml98.pdf
-// Not public API. Only used by tests.
+// Not public API.
 // Remember to update the same function in candid_derive if you change this function.
 #[doc(hidden)]
 #[inline]
diff --git a/rust/candid/src/pretty/candid.rs b/rust/candid/src/pretty/candid.rs
index cb04d68bc..ddbaba342 100644
--- a/rust/candid/src/pretty/candid.rs
+++ b/rust/candid/src/pretty/candid.rs
@@ -2,8 +2,8 @@ use std::collections::HashMap;
 
 use crate::pretty::utils::*;
 use crate::types::{
-    Field, FieldDoc, FuncMode, Function, Label, SharedLabel, Type, TypeDoc, TypeDocs, TypeEnv,
-    TypeInner,
+    ArgType, Field, FieldDoc, FuncMode, Function, Label, SharedLabel, Type, TypeDoc, TypeDocs,
+    TypeEnv, TypeInner,
 };
 use pretty::RcDoc;
 
@@ -100,7 +100,7 @@ pub fn pp_ty_inner(ty: &TypeInner) -> RcDoc<'_> {
         Text => str("text"),
         Reserved => str("reserved"),
         Empty => str("empty"),
-        Var(ref s) => str(s),
+        Var(ref s) => str(s.as_str()),
         Principal => str("principal"),
         Opt(ref t) => kwd("opt").append(pp_ty(t)),
         Vec(ref t) if matches!(t.as_ref(), Nat8) => str("blob"),
@@ -108,8 +108,8 @@ pub fn pp_ty_inner(ty: &TypeInner) -> RcDoc<'_> {
         Record(ref fs) => {
             let t = Type(ty.clone().into());
             if t.is_tuple() {
-                let tuple = concat(fs.iter().map(|f| pp_ty(&f.ty)), ";");
-                kwd("record").append(enclose_space("{", tuple, "}"))
+                let fs = fs.iter().map(|f| pp_ty(&f.ty));
+                kwd("record").append(sep_enclose_space(fs, ";", "{", "}"))
             } else {
                 kwd("record").append(pp_fields(fs, false))
             }
@@ -158,8 +158,7 @@ pub(crate) fn pp_field(field: &Field, is_variant: bool) -> RcDoc<'_> {
 }
 
 fn pp_fields(fs: &[Field], is_variant: bool) -> RcDoc<'_> {
-    let fields = fs.iter().map(|f| pp_field(f, is_variant));
-    enclose_space("{", concat(fields, ";"), "}")
+    sep_enclose_space(fs.iter().map(|f| pp_field(f, is_variant)), ";", "{", "}")
 }
 
 fn pp_field_with_doc<'a>(
@@ -188,7 +187,7 @@ fn pp_fields_with_doc<'a>(
         let field_doc = doc.and_then(|doc| doc.fields.get(&field.id.get_id()));
         pp_field_with_doc(field, is_variant, field_doc)
     });
-    enclose_space("{", concat(fields, ";"), "}")
+    sep_enclose_space(fields, ";", "{", "}")
 }
 
 fn has_field_docs(doc: Option<&TypeDoc>) -> bool {
@@ -201,8 +200,13 @@ fn pp_ty_with_doc<'a>(ty: &'a Type, doc: Option<&'a TypeDoc>) -> RcDoc<'a> {
     match ty.as_ref() {
         Record(ref fs) => {
             if ty.is_tuple() && !has_field_docs(doc) {
-                let tuple = concat(fs.iter().map(|f| pp_ty_with_doc(&f.ty, None)), ";");
-                kwd("record").append(enclose_space("{", tuple, "}"))
+                let tuple = sep_enclose_space(
+                    fs.iter().map(|f| pp_ty_with_doc(&f.ty, None)),
+                    ";",
+                    "{",
+                    "}",
+                );
+                kwd("record").append(tuple)
             } else {
                 kwd("record").append(pp_fields_with_doc(fs, false, doc))
             }
@@ -213,8 +217,8 @@ fn pp_ty_with_doc<'a>(ty: &'a Type, doc: Option<&'a TypeDoc>) -> RcDoc<'a> {
 }
 
 pub fn pp_function(func: &Function) -> RcDoc<'_> {
-    let args = pp_args(&func.args);
-    let rets = pp_rets(&func.rets);
+    let args = pp_named_args(&func.args);
+    let rets = pp_named_args(&func.rets);
     let modes = pp_modes(&func.modes);
     args.append(" ->")
         .append(RcDoc::space())
@@ -222,15 +226,25 @@ pub fn pp_function(func: &Function) -> RcDoc<'_> {
         .nest(INDENT_SPACE)
 }
 
-/// Pretty-prints arguments in the form of `(type1, type2)`.
-pub fn pp_args(args: &[Type]) -> RcDoc<'_> {
-    let doc = concat(args.iter().map(pp_ty), ",");
-    enclose("(", doc, ")")
+/// Pretty-prints named arguments in the form of `(name1 : type1, name2 : type2)`.
+///
+/// To print unnamed arguments, use [`pp_args`] instead.
+pub fn pp_named_args(args: &[ArgType]) -> RcDoc<'_> {
+    let args = args.iter().map(|arg| {
+        if let Some(name) = &arg.name {
+            pp_text(name).append(kwd(" :")).append(pp_ty(&arg.typ))
+        } else {
+            pp_ty(&arg.typ)
+        }
+    });
+    sep_enclose(args, ",", "(", ")")
 }
 
-/// Pretty-prints return types in the form of `(type1, type2)`.
-pub fn pp_rets(args: &[Type]) -> RcDoc<'_> {
-    pp_args(args)
+/// Pretty-prints arguments in the form of `(type1, type2)`.
+///
+/// To print named arguments, use [`pp_named_args`] instead.
+pub fn pp_args(args: &[Type]) -> RcDoc<'_> {
+    sep_enclose(args.iter().map(pp_ty), ",", "(", ")")
 }
 
 pub fn pp_mode(mode: &FuncMode) -> RcDoc<'_> {
@@ -245,28 +259,25 @@ pub fn pp_modes(modes: &[FuncMode]) -> RcDoc<'_> {
 }
 
 fn pp_service<'a>(serv: &'a [(String, Type)], docs: Option<&'a DocComments>) -> RcDoc<'a> {
-    let doc = concat(
-        serv.iter().map(|(id, func)| {
-            let doc = docs
-                .and_then(|docs| docs.lookup_service_method(id))
-                .map(|docs| pp_docs(docs))
-                .unwrap_or(RcDoc::nil());
-            let func_doc = match func.as_ref() {
-                TypeInner::Func(ref f) => pp_function(f),
-                TypeInner::Var(_) => pp_ty(func),
-                _ => unreachable!(),
-            };
-            doc.append(pp_text(id)).append(kwd(" :")).append(func_doc)
-        }),
-        ";",
-    );
-    enclose_space("{", doc, "}")
+    let methods = serv.iter().map(|(id, func)| {
+        let doc = docs
+            .and_then(|docs| docs.lookup_service_method(id))
+            .map(|docs| pp_docs(docs))
+            .unwrap_or(RcDoc::nil());
+        let func_doc = match func.as_ref() {
+            TypeInner::Func(ref f) => pp_function(f),
+            TypeInner::Var(_) => pp_ty(func),
+            _ => unreachable!(),
+        };
+        doc.append(pp_text(id)).append(kwd(" :")).append(func_doc)
+    });
+    sep_enclose_space(methods, ";", "{", "}")
 }
 
 fn pp_defs_plain(env: &TypeEnv) -> RcDoc<'_> {
-    lines(env.0.iter().map(|(id, ty)| {
+    lines(env.to_sorted_iter().map(|(id, ty)| {
         kwd("type")
-            .append(ident(id))
+            .append(ident(id.as_str()))
             .append(kwd("="))
             .append(pp_ty(ty))
             .append(";")
@@ -274,22 +285,22 @@ fn pp_defs_plain(env: &TypeEnv) -> RcDoc<'_> {
 }
 
 fn pp_defs<'a>(env: &'a TypeEnv, docs: &'a DocComments) -> RcDoc<'a> {
-    lines(env.0.iter().map(|(id, ty)| {
-        let type_doc = docs.lookup_type_def(id);
+    lines(env.to_sorted_iter().map(|(id, ty)| {
+        let type_doc = docs.lookup_type_def(id.as_str());
         maybe_pp_docs(type_doc.map(|doc| doc.docs.as_slice()))
             .append(kwd("type"))
-            .append(ident(id))
+            .append(ident(id.as_str()))
             .append(kwd("="))
             .append(pp_ty_with_doc(ty, type_doc))
             .append(";")
     }))
 }
 
-fn pp_class<'a>(args: &'a [Type], t: &'a Type, docs: Option<&'a DocComments>) -> RcDoc<'a> {
-    let doc = pp_args(args).append(" ->").append(RcDoc::space());
+fn pp_class<'a>(args: &'a [ArgType], t: &'a Type, docs: Option<&'a DocComments>) -> RcDoc<'a> {
+    let doc = pp_named_args(args).append(" ->").append(RcDoc::space());
     match t.as_ref() {
         TypeInner::Service(ref serv) => doc.append(pp_service(serv, docs)),
-        TypeInner::Var(ref s) => doc.append(s),
+        TypeInner::Var(ref s) => doc.append(s.as_str()),
         _ => unreachable!(),
     }
 }
@@ -304,10 +315,18 @@ fn pp_actor<'a>(ty: &'a Type, docs: &'a DocComments) -> RcDoc<'a> {
 }
 
 /// Pretty-prints the initialization arguments for a Candid actor.
+///
+/// This function is kept for backward compatibility.
+/// It is recommended to use [`pp_named_init_args`] instead, which prints named arguments.
 pub fn pp_init_args<'a>(env: &'a TypeEnv, args: &'a [Type]) -> RcDoc<'a> {
     pp_defs_plain(env).append(pp_args(args))
 }
 
+/// Pretty-prints the initialization arguments for a Candid actor with named arguments.
+pub fn pp_named_init_args<'a>(env: &'a TypeEnv, args: &'a [ArgType]) -> RcDoc<'a> {
+    pp_defs_plain(env).append(pp_named_args(args))
+}
+
 /// Collects doc comments that can be passed to the [compile_with_docs] function.
 #[derive(Default, Debug)]
 pub struct DocComments {
@@ -594,8 +613,8 @@ pub mod value {
     }
 
     fn pp_fields(depth: usize, fields: &[IDLField]) -> RcDoc<'_> {
-        let fs = concat(fields.iter().map(|f| pp_field(depth, f, false)), ";");
-        enclose_space("{", fs, "}")
+        let fs = fields.iter().map(|f| pp_field(depth, f, false));
+        sep_enclose_space(fs, ";", "{", "}")
     }
 
     pub fn pp_char(v: u8) -> String {
@@ -622,13 +641,13 @@ pub mod value {
                     RcDoc::as_string(format!("{v:?}"))
                 } else {
                     let values = vs.iter().map(|v| pp_value(depth - 1, v));
-                    kwd("vec").append(enclose_space("{", concat(values, ";"), "}"))
+                    kwd("vec").append(sep_enclose_space(values, ";", "{", "}"))
                 }
             }
             Record(fields) => {
                 if is_tuple(v) {
                     let fields = fields.iter().map(|f| pp_value(depth - 1, &f.val));
-                    kwd("record").append(enclose_space("{", concat(fields, ";"), "}"))
+                    kwd("record").append(sep_enclose_space(fields, ";", "{", "}"))
                 } else {
                     kwd("record").append(pp_fields(depth, fields))
                 }
@@ -645,6 +664,6 @@ pub mod value {
             .args
             .iter()
             .map(|v| pp_value(MAX_ELEMENTS_FOR_PRETTY_PRINT, v));
-        enclose("(", concat(args, ","), ")")
+        sep_enclose(args, ",", "(", ")")
     }
 }
diff --git a/rust/candid/src/pretty/utils.rs b/rust/candid/src/pretty/utils.rs
index 9e1a911ef..3b2844f41 100644
--- a/rust/candid/src/pretty/utils.rs
+++ b/rust/candid/src/pretty/utils.rs
@@ -1,45 +1,26 @@
-use pretty::RcDoc;
+use pretty::{RcAllocator, RcDoc};
 
 pub const INDENT_SPACE: isize = 2;
 pub const LINE_WIDTH: usize = 80;
 
-fn is_empty(doc: &RcDoc) -> bool {
-    use pretty::Doc::*;
-    match &**doc {
-        Nil => true,
-        FlatAlt(t1, t2) => is_empty(t2) || is_empty(t1),
-        Union(t1, t2) => is_empty(t1) && is_empty(t2),
-        Group(t) | Nest(_, t) | Annotated((), t) => is_empty(t),
-        _ => false,
-    }
-}
-
 pub fn enclose<'a>(left: &'a str, doc: RcDoc<'a>, right: &'a str) -> RcDoc<'a> {
-    if is_empty(&doc) {
-        RcDoc::text(left).append(right)
-    } else {
-        RcDoc::text(left)
-            .append(RcDoc::line_())
-            .append(doc)
-            .nest(INDENT_SPACE)
-            .append(RcDoc::line_())
-            .append(right)
-            .group()
-    }
+    RcDoc::text(left)
+        .append(RcDoc::line_())
+        .append(doc)
+        .nest(INDENT_SPACE)
+        .append(RcDoc::line_())
+        .append(right)
+        .group()
 }
 
 pub fn enclose_space<'a>(left: &'a str, doc: RcDoc<'a>, right: &'a str) -> RcDoc<'a> {
-    if is_empty(&doc) {
-        RcDoc::text(left).append(right)
-    } else {
-        RcDoc::text(left)
-            .append(RcDoc::line())
-            .append(doc)
-            .nest(INDENT_SPACE)
-            .append(RcDoc::line())
-            .append(right)
-            .group()
-    }
+    RcDoc::text(left)
+        .append(RcDoc::line())
+        .append(doc)
+        .nest(INDENT_SPACE)
+        .append(RcDoc::line())
+        .append(right)
+        .group()
 }
 
 /// Intersperse the separator between each item in `docs`.
@@ -50,20 +31,6 @@ where
     RcDoc::intersperse(docs, RcDoc::text(sep).append(RcDoc::line()))
 }
 
-/// Append the separator to each item in `docs`. If it is displayed in a single line, omit the last separator.
-pub fn concat<'a, D>(docs: D, sep: &'a str) -> RcDoc<'a>
-where
-    D: Iterator<Item = RcDoc<'a>>,
-{
-    let mut docs = docs.peekable();
-    if docs.peek().is_none() {
-        return RcDoc::nil();
-    }
-    let singleline = RcDoc::intersperse(docs, RcDoc::text(sep).append(RcDoc::line()));
-    let multiline = singleline.clone().append(sep);
-    multiline.flat_alt(singleline)
-}
-
 pub fn lines<'a, D>(docs: D) -> RcDoc<'a>
 where
     D: Iterator<Item = RcDoc<'a>>,
@@ -90,15 +57,120 @@ pub fn quote_ident(id: &str) -> RcDoc<'_> {
         .append(RcDoc::space())
 }
 
+/// Separate each item in `docs` with the separator `sep`, and enclose the result in `open` and `close`.
+/// When placed on multiple lines, the last element gets a trailing separator.
+pub fn sep_enclose<'a, D, S, O, C>(docs: D, sep: S, open: O, close: C) -> RcDoc<'a>
+where
+    D: IntoIterator<Item = RcDoc<'a>>,
+    S: pretty::Pretty<'a, RcAllocator>,
+    O: pretty::Pretty<'a, RcAllocator>,
+    C: pretty::Pretty<'a, RcAllocator>,
+{
+    let sep = sep.pretty(&RcAllocator);
+    let elems = RcDoc::intersperse(docs, sep.clone().append(RcDoc::line()));
+    open.pretty(&RcAllocator)
+        .into_doc()
+        .append(RcDoc::line_())
+        .append(elems)
+        .append(sep.flat_alt(RcDoc::nil()))
+        .nest(INDENT_SPACE)
+        .append(RcDoc::line_())
+        .append(close.pretty(&RcAllocator))
+        .group()
+}
+
+/// Like `sep_enclose`, but inserts a space between the opening delimiter and the first element,
+/// and between the last element and the closing delimiter when placed on a single line.
+pub fn sep_enclose_space<'a, D, S, O, C>(docs: D, sep: S, open: O, close: C) -> RcDoc<'a>
+where
+    D: IntoIterator<Item = RcDoc<'a>>,
+    S: pretty::Pretty<'a, RcAllocator>,
+    O: pretty::Pretty<'a, RcAllocator>,
+    C: pretty::Pretty<'a, RcAllocator>,
+{
+    let mut docs = docs.into_iter().peekable();
+    if docs.peek().is_none() {
+        return open.pretty(&RcAllocator).append(close).into_doc();
+    }
+    let open = open
+        .pretty(&RcAllocator)
+        .append(RcDoc::nil().flat_alt(RcDoc::space()));
+    let close = RcDoc::nil().flat_alt(RcDoc::space()).append(close);
+    sep_enclose(docs, sep, open, close)
+}
+
 #[cfg(test)]
-mod test {
+mod tests {
     use super::*;
 
     #[test]
-    fn concat_empty() {
-        let t = concat(vec![].into_iter(), ",")
+    fn enclose_empty() {
+        let t = sep_enclose(vec![], ",", "(", ")")
             .pretty(LINE_WIDTH)
             .to_string();
-        assert_eq!(t, "");
+        assert_eq!(t, "()");
+    }
+
+    #[test]
+    fn enclose_single_line() {
+        let printed = sep_enclose(vec![str("a"), str("b")], ",", "(", ")")
+            .pretty(LINE_WIDTH)
+            .to_string();
+        assert_eq!(printed, "(a, b)");
+    }
+
+    #[test]
+    fn enclose_multiline() {
+        let docs: Vec<RcDoc> = vec![
+            str("Very long line to make sure we get a multiline document"),
+            str("Very long line to make sure we get a multiline document"),
+        ];
+        let printed = sep_enclose(docs, ",", "(", ")").pretty(20).to_string();
+        assert_eq!(
+            printed,
+            "
+(
+  Very long line to make sure we get a multiline document,
+  Very long line to make sure we get a multiline document,
+)
+"
+            .trim()
+        );
+    }
+
+    #[test]
+    fn enclose_empty_space() {
+        let t = sep_enclose_space(vec![], ",", "(", ")")
+            .pretty(LINE_WIDTH)
+            .to_string();
+        assert_eq!(t, "()");
+    }
+
+    #[test]
+    fn enclose_single_line_space() {
+        let printed = sep_enclose_space(vec![str("a"), str("b")], ",", "(", ")")
+            .pretty(LINE_WIDTH)
+            .to_string();
+        assert_eq!(printed, "( a, b )");
+    }
+
+    #[test]
+    fn enclose_multiline_space() {
+        let docs: Vec<RcDoc> = vec![
+            str("Very long line to make sure we get a multiline document"),
+            str("Very long line to make sure we get a multiline document"),
+        ];
+        let printed = sep_enclose_space(docs, ",", "(", ")")
+            .pretty(20)
+            .to_string();
+        assert_eq!(
+            printed,
+            "
+(
+  Very long line to make sure we get a multiline document,
+  Very long line to make sure we get a multiline document,
+)"
+            .trim()
+        );
     }
 }
diff --git a/rust/candid/src/ser.rs b/rust/candid/src/ser.rs
index 6f7bdfdb2..6713b1db7 100644
--- a/rust/candid/src/ser.rs
+++ b/rust/candid/src/ser.rs
@@ -339,20 +339,20 @@ impl TypeSerialize {
                 }
             }
             TypeInner::Func(ref func) => {
-                for ty in func.args.iter().chain(func.rets.iter()) {
-                    self.build_type(ty)?;
+                for ty in &func.args {
+                    self.build_type(&ty.typ)?;
                 }
                 for ty in &func.rets {
-                    self.build_type(ty)?;
+                    self.build_type(&ty.typ)?;
                 }
                 sleb128_encode(&mut buf, Opcode::Func as i64)?;
                 leb128_encode(&mut buf, func.args.len() as u64)?;
                 for ty in &func.args {
-                    self.encode(&mut buf, ty)?;
+                    self.encode(&mut buf, &ty.typ)?;
                 }
                 leb128_encode(&mut buf, func.rets.len() as u64)?;
                 for ty in &func.rets {
-                    self.encode(&mut buf, ty)?;
+                    self.encode(&mut buf, &ty.typ)?;
                 }
                 leb128_encode(&mut buf, func.modes.len() as u64)?;
                 for m in &func.modes {
diff --git a/rust/candid/src/types/internal.rs b/rust/candid/src/types/internal.rs
index e11364879..cd5f11a88 100644
--- a/rust/candid/src/types/internal.rs
+++ b/rust/candid/src/types/internal.rs
@@ -1,9 +1,14 @@
 use super::CandidType;
 use crate::idl_hash;
+use crate::types::type_env::TypeMap;
 use std::cell::RefCell;
 use std::cmp::Ordering;
 use std::collections::BTreeMap;
 use std::fmt;
+use std::fmt::Debug;
+use std::hash::Hash;
+
+pub use crate::types::type_key::TypeKey;
 
 // This is a re-implementation of std::any::TypeId to get rid of 'static constraint.
 // The current TypeId doesn't consider lifetime while computing the hash, which is
@@ -25,7 +30,7 @@ impl TypeId {
 impl std::fmt::Display for TypeId {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let name = NAME.with(|n| n.borrow_mut().get(self));
-        write!(f, "{name}")
+        f.write_str(&name)
     }
 }
 pub fn type_of<T>(_: &T) -> TypeId {
@@ -150,9 +155,10 @@ impl TypeContainer {
                 let id = ID.with(|n| n.borrow().get(t).cloned());
                 if let Some(id) = id {
                     let name = id.to_string();
-                    self.env.0.insert(name.clone(), res);
+                    let type_key = TypeKey::from(name.clone());
+                    self.env.0.insert(type_key.clone(), res);
                     self.remember_named_doc(&id, &name);
-                    TypeInner::Var(name)
+                    TypeInner::Var(type_key)
                 } else {
                     // if the type is part of an enum, the id won't be recorded.
                     // we want to inline the type in this case.
@@ -172,33 +178,56 @@ impl TypeContainer {
                 let id = ID.with(|n| n.borrow().get(t).cloned());
                 if let Some(id) = id {
                     let name = id.to_string();
-                    self.env.0.insert(name.clone(), res);
+                    let type_key = TypeKey::from(name.clone());
+                    self.env.0.insert(type_key.clone(), res);
                     self.remember_named_doc(&id, &name);
-                    TypeInner::Var(name)
+                    TypeInner::Var(type_key)
                 } else {
                     return res;
                 }
             }
             TypeInner::Knot(id) => {
-                let name = id.to_string();
                 let ty = ENV.with(|e| e.borrow().get(id).unwrap().clone());
-                self.env.0.insert(id.to_string(), ty);
+                let name = id.to_string();
+                let type_key = TypeKey::from(name.clone());
+                self.env.0.insert(type_key.clone(), ty);
                 self.remember_named_doc(id, &name);
-                TypeInner::Var(name)
+                TypeInner::Var(type_key)
             }
             TypeInner::Func(func) => TypeInner::Func(Function {
                 modes: func.modes.clone(),
-                args: func.args.iter().map(|arg| self.go(arg)).collect(),
-                rets: func.rets.iter().map(|arg| self.go(arg)).collect(),
+                args: func
+                    .args
+                    .iter()
+                    .map(|arg| ArgType {
+                        name: arg.name.clone(),
+                        typ: self.go(&arg.typ),
+                    })
+                    .collect(),
+                rets: func
+                    .rets
+                    .iter()
+                    .map(|arg| ArgType {
+                        name: arg.name.clone(),
+                        typ: self.go(&arg.typ),
+                    })
+                    .collect(),
             }),
             TypeInner::Service(serv) => TypeInner::Service(
                 serv.iter()
                     .map(|(id, t)| (id.clone(), self.go(t)))
                     .collect(),
             ),
-            TypeInner::Class(inits, ref ty) => {
-                TypeInner::Class(inits.iter().map(|t| self.go(t)).collect(), self.go(ty))
-            }
+            TypeInner::Class(inits, ref ty) => TypeInner::Class(
+                inits
+                    .iter()
+                    .map(|t| ArgType {
+                        name: t.name.clone(),
+                        typ: self.go(&t.typ),
+                    })
+                    .collect(),
+                self.go(ty),
+            ),
             t => t.clone(),
         }
         .into()
@@ -236,7 +265,7 @@ pub enum TypeInner {
     Reserved,
     Empty,
     Knot(TypeId), // For recursive types from Rust
-    Var(String),  // For variables from Candid file
+    Var(TypeKey), // For variables from Candid file
     Unknown,
     Opt(Type),
     Vec(Type),
@@ -244,7 +273,7 @@ pub enum TypeInner {
     Variant(Vec<Field>),
     Func(Function),
     Service(Vec<(String, Type)>),
-    Class(Vec<Type>, Type),
+    Class(Vec<ArgType>, Type),
     Principal,
     Future,
 }
@@ -297,12 +326,12 @@ impl Type {
     pub fn is_blob(&self, env: &crate::TypeEnv) -> bool {
         self.as_ref().is_blob(env)
     }
-    pub fn subst(&self, tau: &std::collections::BTreeMap<String, String>) -> Self {
+    pub fn subst(&self, tau: &TypeMap<TypeKey>) -> Self {
         use TypeInner::*;
         match self.as_ref() {
             Var(id) => match tau.get(id) {
-                None => Var(id.to_string()),
-                Some(new_id) => Var(new_id.to_string()),
+                None => Var(id.clone()),
+                Some(new_id) => Var(new_id.clone()),
             },
             Opt(t) => Opt(t.subst(tau)),
             Vec(t) => Vec(t.subst(tau)),
@@ -326,8 +355,22 @@ impl Type {
                 let func = func.clone();
                 Func(Function {
                     modes: func.modes,
-                    args: func.args.into_iter().map(|t| t.subst(tau)).collect(),
-                    rets: func.rets.into_iter().map(|t| t.subst(tau)).collect(),
+                    args: func
+                        .args
+                        .into_iter()
+                        .map(|t| ArgType {
+                            name: t.name,
+                            typ: t.typ.subst(tau),
+                        })
+                        .collect(),
+                    rets: func
+                        .rets
+                        .into_iter()
+                        .map(|t| ArgType {
+                            name: t.name,
+                            typ: t.typ.subst(tau),
+                        })
+                        .collect(),
                 })
             }
             Service(serv) => Service(
@@ -335,7 +378,15 @@ impl Type {
                     .map(|(meth, ty)| (meth.clone(), ty.subst(tau)))
                     .collect(),
             ),
-            Class(args, ty) => Class(args.iter().map(|t| t.subst(tau)).collect(), ty.subst(tau)),
+            Class(args, ty) => Class(
+                args.iter()
+                    .map(|t| ArgType {
+                        name: t.name.clone(),
+                        typ: t.typ.subst(tau),
+                    })
+                    .collect(),
+                ty.subst(tau),
+            ),
             _ => return self.clone(),
         }
         .into()
@@ -379,7 +430,7 @@ pub fn text_size(t: &Type, limit: i32) -> Result<i32, ()> {
         Reserved => 8,
         Principal => 9,
         Knot(_) => 10,
-        Var(id) => id.len() as i32,
+        Var(id) => id.as_str().len() as i32,
         Opt(t) => 4 + text_size(t, limit - 4)?,
         Vec(t) => 4 + text_size(t, limit - 4)?,
         Record(fs) | Variant(fs) => {
@@ -401,11 +452,16 @@ pub fn text_size(t: &Type, limit: i32) -> Result<i32, ()> {
             let mut cnt = mode + 6;
             let mut limit = limit - cnt;
             for t in &func.args {
-                cnt += text_size(t, limit)?;
+                if let Some(name) = t.name.as_ref() {
+                    let id_size = name.len() as i32;
+                    cnt += id_size + text_size(&t.typ, limit - id_size - 3)? + 3;
+                } else {
+                    cnt += text_size(&t.typ, limit)?;
+                }
                 limit -= cnt;
             }
             for t in &func.rets {
-                cnt += text_size(t, limit)?;
+                cnt += text_size(&t.typ, limit)?;
                 limit -= cnt;
             }
             cnt
@@ -558,8 +614,14 @@ pub enum FuncMode {
 #[derive(Debug, PartialEq, Hash, Eq, Clone, PartialOrd, Ord)]
 pub struct Function {
     pub modes: Vec<FuncMode>,
-    pub args: Vec<Type>,
-    pub rets: Vec<Type>,
+    pub args: Vec<ArgType>,
+    pub rets: Vec<ArgType>,
+}
+
+#[derive(Debug, PartialEq, Hash, Eq, Clone, PartialOrd, Ord)]
+pub struct ArgType {
+    pub name: Option<String>,
+    pub typ: Type,
 }
 
 #[cfg(feature = "printer")]
@@ -588,16 +650,16 @@ impl Function {
 /// `func!((u8, &str) -> (Nat) query)` expands to `Type(Rc::new(TypeInner::Func(...)))`
 macro_rules! func {
     ( ( $($arg:ty),* $(,)? ) -> ( $($ret:ty),* $(,)? ) ) => {
-        Into::<$crate::types::Type>::into($crate::types::TypeInner::Func($crate::types::Function { args: vec![$(<$arg>::ty()),*], rets: vec![$(<$ret>::ty()),*], modes: vec![] }))
+        Into::<$crate::types::Type>::into($crate::types::TypeInner::Func($crate::types::Function { args: vec![$(<$arg>::ty()),*].into_iter().map(|arg| $crate::types::ArgType { name: None, typ: arg }).collect(), rets: vec![$(<$ret>::ty()),*].into_iter().map(|ret| $crate::types::ArgType { name: None, typ: ret }).collect(), modes: vec![] }))
     };
     ( ( $($arg:ty),* $(,)? ) -> ( $($ret:ty),* $(,)? ) query ) => {
-        Into::<$crate::types::Type>::into($crate::types::TypeInner::Func($crate::types::Function { args: vec![$(<$arg>::ty()),*], rets: vec![$(<$ret>::ty()),*], modes: vec![$crate::types::FuncMode::Query] }))
+        Into::<$crate::types::Type>::into($crate::types::TypeInner::Func($crate::types::Function { args: vec![$(<$arg>::ty()),*].into_iter().map(|arg| $crate::types::ArgType { name: None, typ: arg }).collect(), rets: vec![$(<$ret>::ty()),*].into_iter().map(|ret| $crate::types::ArgType { name: None, typ: ret }).collect(), modes: vec![$crate::types::FuncMode::Query] }))
     };
     ( ( $($arg:ty),* $(,)? ) -> ( $($ret:ty),* $(,)? ) composite_query ) => {
-        Into::<$crate::types::Type>::into($crate::types::TypeInner::Func($crate::types::Function { args: vec![$(<$arg>::ty()),*], rets: vec![$(<$ret>::ty()),*], modes: vec![$crate::types::FuncMode::CompositeQuery] }))
+        Into::<$crate::types::Type>::into($crate::types::TypeInner::Func($crate::types::Function { args: vec![$(<$arg>::ty()),*].into_iter().map(|arg| $crate::types::ArgType { name: None, typ: arg }).collect(), rets: vec![$(<$ret>::ty()),*].into_iter().map(|ret| $crate::types::ArgType { name: None, typ: ret }).collect(), modes: vec![$crate::types::FuncMode::CompositeQuery] }))
     };
     ( ( $($arg:ty),* $(,)? ) -> ( $($ret:ty),* $(,)? ) oneway ) => {
-        Into::<$crate::types::Type>::into($crate::types::TypeInner::Func($crate::types::Function { args: vec![$(<$arg>::ty()),*], rets: vec![$(<$ret>::ty()),*], modes: vec![$crate::types::FuncMode::Oneway] }))
+        Into::<$crate::types::Type>::into($crate::types::TypeInner::Func($crate::types::Function { args: vec![$(<$arg>::ty()),*].into_iter().map(|arg| $crate::types::ArgType { name: None, typ: arg }).collect(), rets: vec![$(<$ret>::ty()),*].into_iter().map(|ret| $crate::types::ArgType { name: None, typ: ret }).collect(), modes: vec![$crate::types::FuncMode::Oneway] }))
     };
 }
 #[macro_export]
diff --git a/rust/candid/src/types/mod.rs b/rust/candid/src/types/mod.rs
index 06a28daf8..4102a9198 100644
--- a/rust/candid/src/types/mod.rs
+++ b/rust/candid/src/types/mod.rs
@@ -15,8 +15,8 @@ pub mod type_env;
 pub mod value;
 
 pub use self::internal::{
-    get_type, Field, FieldDoc, FuncMode, Function, Label, SharedLabel, Type, TypeDoc, TypeDocs,
-    TypeId, TypeInner,
+    get_type, ArgType, Field, FieldDoc, FuncMode, Function, Label, SharedLabel, Type, TypeDoc,
+    TypeDocs, TypeId, TypeInner,
 };
 pub use type_env::TypeEnv;
 
@@ -31,6 +31,7 @@ pub mod result;
 
 pub mod arc;
 pub mod rc;
+mod type_key;
 
 pub trait CandidType {
     // memoized type derivation
diff --git a/rust/candid/src/types/subtype.rs b/rust/candid/src/types/subtype.rs
index bf3027aff..11e535df2 100644
--- a/rust/candid/src/types/subtype.rs
+++ b/rust/candid/src/types/subtype.rs
@@ -1,5 +1,5 @@
 use super::internal::{find_type, Field, Label, Type, TypeInner};
-use crate::types::TypeEnv;
+use crate::types::{ArgType, TypeEnv};
 use crate::utils::RecursionDepth;
 use crate::{Error, Result};
 use anyhow::Context;
@@ -441,8 +441,8 @@ fn check_func_params(
     report: OptReport,
     gamma: &mut Gamma,
     env: &TypeEnv,
-    sub_params: &[Type],
-    sup_params: &[Type],
+    sub_params: &[ArgType],
+    sup_params: &[ArgType],
     depth: &RecursionDepth,
     path: &mut Vec<String>,
     errors: &mut Vec<Incompatibility>,
@@ -457,8 +457,8 @@ fn check_func_params(
             report,
             gamma,
             env,
-            &sub_params[0],
-            &sup_params[0],
+            &sub_params[0].typ,
+            &sup_params[0].typ,
             depth,
             path,
             errors,
@@ -797,20 +797,20 @@ where
     }
 }
 
-fn to_tuple(args: &[Type]) -> Type {
+fn to_tuple(args: &[ArgType]) -> Type {
     TypeInner::Record(
         args.iter()
             .enumerate()
-            .map(|(i, ty)| Field {
+            .map(|(i, arg)| Field {
                 id: Label::Id(i as u32).into(),
-                ty: ty.clone(),
+                ty: arg.typ.clone(),
             })
             .collect(),
     )
     .into()
 }
 #[cfg(not(feature = "printer"))]
-fn pp_args(args: &[crate::types::Type]) -> String {
+fn pp_args(args: &[crate::types::ArgType]) -> String {
     use std::fmt::Write;
     let mut s = String::new();
     write!(&mut s, "(").unwrap();
@@ -821,7 +821,7 @@ fn pp_args(args: &[crate::types::Type]) -> String {
     s
 }
 #[cfg(feature = "printer")]
-fn pp_args(args: &[crate::types::Type]) -> String {
-    use crate::pretty::candid::pp_args;
-    pp_args(args).pretty(80).to_string()
+fn pp_args(args: &[crate::types::ArgType]) -> String {
+    use crate::pretty::candid::pp_named_args;
+    pp_named_args(args).pretty(80).to_string()
 }
diff --git a/rust/candid/src/types/type_env.rs b/rust/candid/src/types/type_env.rs
index d66e209fd..0d22f7900 100644
--- a/rust/candid/src/types/type_env.rs
+++ b/rust/candid/src/types/type_env.rs
@@ -1,18 +1,23 @@
+use crate::types::internal::TypeKey;
 use crate::types::{Function, Type, TypeInner};
 use crate::utils::RecursionDepth;
 use crate::{Error, Result};
-use std::collections::BTreeMap;
+use foldhash::fast::FixedState;
+use hashbrown::HashMap;
+
+pub type TypeMap<V> = HashMap<TypeKey, V, FixedState>;
 
 #[derive(Debug, Clone, Default)]
-pub struct TypeEnv(pub BTreeMap<String, Type>);
+pub struct TypeEnv(pub TypeMap<Type>);
 
 impl TypeEnv {
     pub fn new() -> Self {
-        TypeEnv(BTreeMap::new())
+        TypeEnv(TypeMap::default())
     }
+
     pub fn merge<'a>(&'a mut self, env: &TypeEnv) -> Result<&'a mut Self> {
-        for (k, v) in &env.0 {
-            let entry = self.0.entry(k.to_string()).or_insert_with(|| v.clone());
+        for (k, v) in env.0.iter() {
+            let entry = self.0.entry(k.clone()).or_insert_with(|| v.clone());
             if *entry != *v {
                 return Err(Error::msg("inconsistent binding"));
             }
@@ -20,11 +25,11 @@ impl TypeEnv {
         Ok(self)
     }
     pub fn merge_type(&mut self, env: TypeEnv, ty: Type) -> Type {
-        let tau: BTreeMap<String, String> = env
+        let tau: TypeMap<TypeKey> = env
             .0
             .keys()
             .filter(|k| self.0.contains_key(*k))
-            .map(|k| (k.clone(), format!("{k}/1")))
+            .map(|k| (k.clone(), format!("{k}/1").into()))
             .collect();
         for (k, t) in env.0 {
             let t = t.subst(&tau);
@@ -36,18 +41,19 @@ impl TypeEnv {
         }
         ty.subst(&tau)
     }
-    pub fn find_type(&self, name: &str) -> Result<&Type> {
-        match self.0.get(name) {
-            None => Err(Error::msg(format!("Unbound type identifier {name}"))),
+    pub fn find_type(&self, key: &TypeKey) -> Result<&Type> {
+        match self.0.get(key) {
+            None => Err(Error::msg(format!("Unbound type identifier {key}"))),
             Some(t) => Ok(t),
         }
     }
-    pub fn rec_find_type(&self, name: &str) -> Result<&Type> {
+
+    pub fn rec_find_type(&self, name: &TypeKey) -> Result<&Type> {
         self.rec_find_type_with_depth(name, &RecursionDepth::new())
     }
     pub(crate) fn rec_find_type_with_depth(
         &self,
-        name: &str,
+        name: &TypeKey,
         depth: &RecursionDepth,
     ) -> Result<&Type> {
         let _guard = depth.guard()?;
@@ -115,8 +121,8 @@ impl TypeEnv {
     }
     fn is_empty<'a>(
         &'a self,
-        res: &mut BTreeMap<&'a str, Option<bool>>,
-        id: &'a str,
+        res: &mut HashMap<&'a TypeKey, Option<bool>, FixedState>,
+        id: &'a TypeKey,
         depth: &RecursionDepth,
     ) -> Result<bool> {
         let _guard = depth.guard()?;
@@ -152,24 +158,34 @@ impl TypeEnv {
         Ok(result)
     }
     pub fn replace_empty(&mut self) -> Result<()> {
-        let mut res = BTreeMap::new();
-        for name in self.0.keys() {
-            self.is_empty(&mut res, name, &RecursionDepth::new())?;
+        let mut res = HashMap::default();
+        for key in self.0.keys() {
+            self.is_empty(&mut res, key, &RecursionDepth::new())?;
         }
         let ids: Vec<_> = res
-            .iter()
+            .into_iter()
             .filter(|(_, v)| matches!(v, Some(true)))
-            .map(|(id, _)| id.to_string())
+            .map(|(id, _)| id.to_owned())
             .collect();
         for id in ids {
             self.0.insert(id, TypeInner::Empty.into());
         }
         Ok(())
     }
+
+    /// Creates an iterator that iterates over the types in the order of keys.
+    ///
+    /// The implementation collects elements into a temporary vector and sorts the vector.
+    pub fn to_sorted_iter(&self) -> impl Iterator<Item = (&TypeKey, &Type)> {
+        let mut vec: Vec<_> = self.0.iter().collect();
+        vec.sort_unstable_by_key(|elem| elem.0);
+        vec.into_iter()
+    }
 }
+
 impl std::fmt::Display for TypeEnv {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        for (k, v) in &self.0 {
+        for (k, v) in self.to_sorted_iter() {
             writeln!(f, "type {k} = {v}")?;
         }
         Ok(())
diff --git a/rust/candid/src/types/type_key.rs b/rust/candid/src/types/type_key.rs
new file mode 100644
index 000000000..238f37b29
--- /dev/null
+++ b/rust/candid/src/types/type_key.rs
@@ -0,0 +1,230 @@
+use crate::idl_hash;
+use std::cell::OnceCell;
+use std::cmp::Ordering;
+use std::fmt;
+use std::fmt::{Debug, Display, Formatter};
+use std::hash::{Hash, Hasher};
+use std::str::FromStr;
+
+#[derive(Clone)]
+enum TypeKeyInner {
+    Indexed { index: i64, name: OnceCell<String> },
+    Named { name: String, hash: u32 },
+}
+
+impl TypeKeyInner {
+    pub fn as_str(&self) -> &str {
+        match self {
+            TypeKeyInner::Indexed { index, name } => {
+                name.get_or_init(|| TypeKey::name_from_index(*index))
+            }
+            TypeKeyInner::Named { name, .. } => name,
+        }
+    }
+}
+
+impl Debug for TypeKeyInner {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.write_str(self.as_str())
+    }
+}
+
+/// A `TypeKey` represents a type from a Candid schema. The type can be string-based or index-based.
+#[derive(Debug, Clone)]
+pub struct TypeKey(TypeKeyInner);
+
+impl TypeKey {
+    const INDEXED_PREFIX: &'static str = "table";
+
+    pub fn indexed(idx: i64) -> Self {
+        TypeKeyInner::Indexed {
+            index: idx,
+            name: Default::default(),
+        }
+        .into()
+    }
+
+    pub fn as_str(&self) -> &str {
+        self.0.as_str()
+    }
+
+    fn name_from_index(i: i64) -> String {
+        format!("{}{}", Self::INDEXED_PREFIX, i)
+    }
+
+    fn maybe_indexed(value: &str) -> Option<TypeKey> {
+        let index = i64::from_str(value.strip_prefix(Self::INDEXED_PREFIX)?).ok()?;
+        Some(TypeKey::indexed(index))
+    }
+}
+
+impl From<TypeKeyInner> for TypeKey {
+    fn from(value: TypeKeyInner) -> Self {
+        Self(value)
+    }
+}
+
+impl PartialOrd for TypeKey {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl Ord for TypeKey {
+    fn cmp(&self, other: &Self) -> Ordering {
+        // If the performance of this function ever becomes too slow, the function can be optimized
+        // by specializing comparison of two TypeKeyInner::Indexed objects.
+        self.as_str().cmp(other.as_str())
+    }
+}
+
+impl PartialEq for TypeKey {
+    fn eq(&self, other: &Self) -> bool {
+        match (&self.0, &other.0) {
+            (
+                TypeKeyInner::Indexed { index: index1, .. },
+                TypeKeyInner::Indexed { index: index2, .. },
+            ) => *index1 == *index2,
+            (
+                TypeKeyInner::Named {
+                    hash: hash1,
+                    name: name1,
+                },
+                TypeKeyInner::Named {
+                    hash: hash2,
+                    name: name2,
+                },
+            ) => *hash1 == *hash2 && name1 == name2,
+            _ => false,
+        }
+    }
+}
+
+impl Eq for TypeKey {}
+
+impl Hash for TypeKey {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        match &self.0 {
+            TypeKeyInner::Indexed { index, .. } => index.hash(state),
+            TypeKeyInner::Named { hash, .. } => hash.hash(state),
+        }
+    }
+}
+
+impl Display for TypeKey {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.write_str(self.as_str())
+    }
+}
+
+impl From<String> for TypeKey {
+    fn from(value: String) -> Self {
+        Self::maybe_indexed(&value).unwrap_or_else(|| {
+            TypeKeyInner::Named {
+                hash: idl_hash(&value),
+                name: value,
+            }
+            .into()
+        })
+    }
+}
+
+impl From<&str> for TypeKey {
+    fn from(value: &str) -> Self {
+        Self::maybe_indexed(value).unwrap_or_else(|| {
+            TypeKeyInner::Named {
+                hash: idl_hash(value),
+                name: value.to_string(),
+            }
+            .into()
+        })
+    }
+}
+
+impl AsRef<str> for TypeKey {
+    fn as_ref(&self) -> &str {
+        self.as_str()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::collections::HashMap;
+
+    #[test]
+    fn type_key_indexed_name() {
+        assert_eq!(TypeKey::indexed(42).as_str(), "table42");
+    }
+
+    #[test]
+    fn type_key_from_string() {
+        assert_eq!(TypeKey::from("foobar"), TypeKey::from("foobar".to_string()));
+        assert_eq!(TypeKey::from("foobar").as_str(), "foobar");
+        assert_eq!(TypeKey::from("table").as_str(), "table");
+        // Check that indexed keys with a "broken" index are parsed correctly.
+        assert_eq!(TypeKey::from("table3.5").as_str(), "table3.5");
+        assert_eq!(TypeKey::from("table-33").as_str(), "table-33");
+    }
+
+    #[test]
+    fn type_key_indexed() {
+        assert_eq!(TypeKey::from("table33"), TypeKey::indexed(33));
+    }
+
+    #[test]
+    fn type_key_hash() {
+        let mut map = HashMap::new();
+        map.insert(TypeKey::from("a"), 1);
+        map.insert(TypeKey::from("bar".to_string()), 2);
+        map.insert(TypeKey::from("table1"), 3);
+        map.insert(TypeKey::from("table97"), 4);
+        map.insert(TypeKey::indexed(33), 5);
+
+        assert_eq!(map.get(&"a".to_string().into()), Some(&1));
+        assert_eq!(map.get(&"bar".into()), Some(&2));
+        assert_eq!(map.get(&TypeKey::indexed(1)), Some(&3));
+        assert_eq!(map.get(&TypeKey::indexed(97)), Some(&4));
+        assert_eq!(map.get(&TypeKey::from("table33")), Some(&5));
+    }
+
+    #[test]
+    fn type_key_ord() {
+        let mut keys = vec![
+            TypeKey::indexed(4),
+            TypeKey::indexed(24),
+            TypeKey::from("table3"),
+            TypeKey::from("table"),
+            TypeKey::indexed(1),
+            TypeKey::from("table23"),
+            TypeKey::from("table4.3"),
+            TypeKey::from("zzz"),
+            TypeKey::from("a"),
+        ];
+
+        let expected = vec![
+            TypeKey::from("a"),
+            TypeKey::from("table"),
+            TypeKey::indexed(1),
+            TypeKey::from("table23"),
+            // Note that even though 3 < 24 and 4 < 24, they're ordered afterward because we use
+            // string-based ordering to maintain consistency between named and indexed TypeKeys.
+            TypeKey::indexed(24),
+            TypeKey::from("table3"),
+            TypeKey::indexed(4),
+            TypeKey::from("table4.3"),
+            TypeKey::from("zzz"),
+        ];
+        keys.sort_unstable();
+        assert_eq!(keys, expected);
+    }
+
+    #[test]
+    fn type_key_to_string() {
+        assert_eq!(TypeKey::indexed(32).to_string(), "table32");
+        assert_eq!(TypeKey::from("foo").to_string(), "foo");
+        // debug string
+        assert_eq!(format!("{:?}", TypeKey::indexed(32)), "TypeKey(table32)");
+        assert_eq!(format!("{:?}", TypeKey::from("foo")), "TypeKey(foo)");
+    }
+}
diff --git a/rust/candid/tests/types.rs b/rust/candid/tests/types.rs
index 5de3ab2df..0d37f8f04 100644
--- a/rust/candid/tests/types.rs
+++ b/rust/candid/tests/types.rs
@@ -308,7 +308,7 @@ service : (List_2) -> {
   // on multiple lines
   "oneway" : (text) -> () oneway;
   // Doc comment for 🐂
-  "🐂" : (text, int32) -> (text, int32) query;
+  "🐂" : (a : text, b : int32) -> (text, int32) query;
 }"#;
     assert_eq!(expected, __export_service());
 }
@@ -336,7 +336,22 @@ fn test_counter() {
         }
     }
     candid::export_service!();
-    let expected = "service : { inc : () -> (); read : () -> (nat64) query; set : (nat64) -> () }";
+    let expected = r#"service : {
+  inc : () -> ();
+  read : () -> (nat64) query;
+  set : (value : nat64) -> ();
+}"#;
+    assert_eq!(expected, __export_service());
+}
+
+#[test]
+fn test_init_named_args() {
+    #[candid_method(init)]
+    fn init(a: u8) {
+        let _ = a;
+    }
+    candid::export_service!();
+    let expected = r#"service : (a : nat8) -> {}"#;
     assert_eq!(expected, __export_service());
 }
 
diff --git a/rust/candid_derive/src/func.rs b/rust/candid_derive/src/func.rs
index 65cb1cc95..ed31f9ec1 100644
--- a/rust/candid_derive/src/func.rs
+++ b/rust/candid_derive/src/func.rs
@@ -6,9 +6,9 @@ use std::collections::BTreeMap;
 use std::sync::Mutex;
 use syn::{Error, ItemFn, Meta, Result, ReturnType, Signature, Type};
 
-type RawArgs = Vec<String>;
+type RawArgs = Vec<(Option<String>, String)>;
 type RawRets = Vec<String>;
-type ParsedArgs = Vec<Type>;
+type ParsedArgs = Vec<(Option<String>, Type)>;
 type ParsedRets = Vec<Type>;
 
 struct Method {
@@ -43,7 +43,7 @@ pub(crate) fn candid_method(attrs: Vec<Meta>, fun: ItemFn) -> Result<TokenStream
     let (args, rets) = get_args(sig)?;
     let args: RawArgs = args
         .iter()
-        .map(|t| format!("{}", t.to_token_stream()))
+        .map(|(name, t)| (name.clone(), format!("{}", t.to_token_stream())))
         .collect();
     let rets: RawRets = rets
         .iter()
@@ -94,7 +94,7 @@ pub(crate) fn export_service(path: Option<TokenStream>) -> TokenStream {
                     .map(|t| generate_arg(quote! { init_args }, t))
                     .collect::<Vec<_>>();
                 quote! {
-                    let mut init_args: Vec<Type> = Vec::new();
+                    let mut init_args: Vec<ArgType> = Vec::new();
                     #(#args)*
                 }
             });
@@ -138,9 +138,9 @@ pub(crate) fn export_service(path: Option<TokenStream>) -> TokenStream {
                 quote! {
                     {
                         #doc_storage
-                        let mut args: Vec<Type> = Vec::new();
+                        let mut args: Vec<ArgType> = Vec::new();
                         #(#args)*
-                        let mut rets: Vec<Type> = Vec::new();
+                        let mut rets: Vec<ArgType> = Vec::new();
                         #(#rets)*
                         let func = Function { args, rets, modes: #modes };
                         service.push((#name.to_string(), TypeInner::Func(func).into()));
@@ -149,7 +149,7 @@ pub(crate) fn export_service(path: Option<TokenStream>) -> TokenStream {
             },
         );
         let service = quote! {
-            use #candid::types::{CandidType, Function, Type, TypeInner};
+            use #candid::types::{CandidType, Function, Type, ArgType, TypeInner};
             let mut service = Vec::<(String, Type)>::new();
             let mut env = #candid::types::internal::TypeContainer::new();
             let mut docs = #candid::pretty::candid::DocComments::empty();
@@ -182,15 +182,22 @@ pub(crate) fn export_service(path: Option<TokenStream>) -> TokenStream {
     }
 }
 
-fn generate_arg(name: TokenStream, ty: &str) -> TokenStream {
-    let ty = syn::parse_str::<Type>(ty).unwrap();
+fn generate_arg(name: TokenStream, (arg_name, ty): &(Option<String>, String)) -> TokenStream {
+    let arg_name = arg_name
+        .as_ref()
+        .map(|n| quote! { Some(#n.to_string()) })
+        .unwrap_or(quote! { None });
+    let ty = syn::parse_str::<Type>(ty.as_str()).unwrap();
     quote! {
-        #name.push(env.add::<#ty>());
+        #name.push(ArgType { name: #arg_name, typ: env.add::<#ty>() });
     }
 }
 
 fn generate_ret(name: TokenStream, ty: &str) -> TokenStream {
-    generate_arg(name, ty)
+    let ty = syn::parse_str::<Type>(ty).unwrap();
+    quote! {
+        #name.push(ArgType { name: None, typ: env.add::<#ty>() });
+    }
 }
 
 fn get_args(sig: &Signature) -> Result<(ParsedArgs, ParsedRets)> {
@@ -202,7 +209,20 @@ fn get_args(sig: &Signature) -> Result<(ParsedArgs, ParsedRets)> {
                     return Err(Error::new_spanned(arg, "only works for borrowed self"));
                 }
             }
-            syn::FnArg::Typed(syn::PatType { ty, .. }) => args.push(ty.as_ref().clone()),
+            syn::FnArg::Typed(syn::PatType { ty, pat, .. }) => {
+                if let syn::Pat::Ident(syn::PatIdent { ident, .. }) = pat.as_ref() {
+                    let arg_name = ident.to_string();
+                    if arg_name.starts_with("_") {
+                        // If the argument name starts with _, it usually means it's not used.
+                        // We don't need to include it in the IDL.
+                        args.push((None, ty.as_ref().clone()));
+                    } else {
+                        args.push((Some(arg_name), ty.as_ref().clone()));
+                    }
+                } else {
+                    args.push((None, ty.as_ref().clone()));
+                }
+            }
         }
     }
     let rets = match &sig.output {
diff --git a/rust/candid_parser/src/bindings/analysis.rs b/rust/candid_parser/src/bindings/analysis.rs
index 2633c6f08..cf14e2e76 100644
--- a/rust/candid_parser/src/bindings/analysis.rs
+++ b/rust/candid_parser/src/bindings/analysis.rs
@@ -1,4 +1,5 @@
 use crate::{Error, Result};
+use candid::types::internal::TypeKey;
 use candid::types::{Type, TypeEnv, TypeInner};
 use std::collections::{BTreeMap, BTreeSet};
 
@@ -42,10 +43,12 @@ pub fn chase_type<'a>(
 ) -> Result<()> {
     use TypeInner::*;
     match t.as_ref() {
-        Var(id) if seen.insert(id) => {
-            let t = env.find_type(id)?;
-            chase_type(seen, res, env, t)?;
-            res.push(id);
+        Var(id) => {
+            if seen.insert(id.as_str()) {
+                let t = env.find_type(id)?;
+                chase_type(seen, res, env, t)?;
+                res.push(id.as_str());
+            }
         }
         Opt(ty) | Vec(ty) => chase_type(seen, res, env, ty)?,
         Record(fs) | Variant(fs) => {
@@ -54,7 +57,9 @@ pub fn chase_type<'a>(
             }
         }
         Func(f) => {
-            for ty in f.args.iter().chain(f.rets.iter()) {
+            let args = f.args.iter().map(|arg| &arg.typ);
+            let rets = f.rets.iter().map(|ret| &ret.typ);
+            for ty in args.chain(rets) {
                 chase_type(seen, res, env, ty)?;
             }
         }
@@ -65,7 +70,7 @@ pub fn chase_type<'a>(
         }
         Class(args, t) => {
             for arg in args.iter() {
-                chase_type(seen, res, env, arg)?;
+                chase_type(seen, res, env, &arg.typ)?;
             }
             chase_type(seen, res, env, t)?;
         }
@@ -92,7 +97,7 @@ pub fn chase_def_use<'a>(
     if let TypeInner::Class(args, _) = actor.as_ref() {
         for (i, arg) in args.iter().enumerate() {
             let mut used = Vec::new();
-            chase_type(&mut BTreeSet::new(), &mut used, env, arg)?;
+            chase_type(&mut BTreeSet::new(), &mut used, env, &arg.typ)?;
             for var in used {
                 res.entry(var.to_string())
                     .or_insert_with(Vec::new)
@@ -104,7 +109,7 @@ pub fn chase_def_use<'a>(
         let func = env.as_func(ty)?;
         for (i, arg) in func.args.iter().enumerate() {
             let mut used = Vec::new();
-            chase_type(&mut BTreeSet::new(), &mut used, env, arg)?;
+            chase_type(&mut BTreeSet::new(), &mut used, env, &arg.typ)?;
             for var in used {
                 res.entry(var.to_string())
                     .or_insert_with(Vec::new)
@@ -113,7 +118,7 @@ pub fn chase_def_use<'a>(
         }
         for (i, arg) in func.rets.iter().enumerate() {
             let mut used = Vec::new();
-            chase_type(&mut BTreeSet::new(), &mut used, env, arg)?;
+            chase_type(&mut BTreeSet::new(), &mut used, env, &arg.typ)?;
             for var in used {
                 res.entry(var.to_string())
                     .or_insert_with(Vec::new)
@@ -145,8 +150,10 @@ pub fn infer_rec<'a>(_env: &'a TypeEnv, def_list: &'a [&'a str]) -> Result<BTree
     ) -> Result<()> {
         use TypeInner::*;
         match t.as_ref() {
-            Var(id) if seen.insert(id) => {
-                res.insert(id);
+            Var(id) => {
+                if seen.insert(id.as_str()) {
+                    res.insert(id.as_str());
+                }
             }
             Opt(ty) | Vec(ty) => go(seen, res, _env, ty)?,
             Record(fs) | Variant(fs) => {
@@ -155,7 +162,9 @@ pub fn infer_rec<'a>(_env: &'a TypeEnv, def_list: &'a [&'a str]) -> Result<BTree
                 }
             }
             Func(f) => {
-                for ty in f.args.iter().chain(f.rets.iter()) {
+                let args = f.args.iter().map(|arg| &arg.typ);
+                let rets = f.rets.iter().map(|ret| &ret.typ);
+                for ty in args.chain(rets) {
                     go(seen, res, _env, ty)?;
                 }
             }
@@ -166,7 +175,7 @@ pub fn infer_rec<'a>(_env: &'a TypeEnv, def_list: &'a [&'a str]) -> Result<BTree
             }
             Class(args, t) => {
                 for arg in args.iter() {
-                    go(seen, res, _env, arg)?;
+                    go(seen, res, _env, &arg.typ)?;
                 }
                 go(seen, res, _env, t)?;
             }
@@ -174,8 +183,8 @@ pub fn infer_rec<'a>(_env: &'a TypeEnv, def_list: &'a [&'a str]) -> Result<BTree
         }
         Ok(())
     }
-    for var in def_list.iter() {
-        let t = _env.0.get(*var).unwrap();
+    for &var in def_list.iter() {
+        let t = _env.0.get(&TypeKey::from(var)).unwrap();
         go(&mut seen, &mut res, _env, t)?;
         seen.insert(var);
     }
diff --git a/rust/candid_parser/src/bindings/javascript.rs b/rust/candid_parser/src/bindings/javascript.rs
index 3b8e4621c..92b6a7a98 100644
--- a/rust/candid_parser/src/bindings/javascript.rs
+++ b/rust/candid_parser/src/bindings/javascript.rs
@@ -1,7 +1,7 @@
 use super::analysis::{chase_actor, chase_types, infer_rec};
 use candid::pretty::candid::pp_mode;
 use candid::pretty::utils::*;
-use candid::types::{Field, Function, Label, SharedLabel, Type, TypeEnv, TypeInner};
+use candid::types::{ArgType, Field, Function, Label, SharedLabel, Type, TypeEnv, TypeInner};
 use pretty::RcDoc;
 use std::collections::BTreeSet;
 
@@ -119,14 +119,14 @@ fn pp_ty(ty: &Type) -> RcDoc<'_> {
         Text => str("IDL.Text"),
         Reserved => str("IDL.Reserved"),
         Empty => str("IDL.Empty"),
-        Var(ref s) => ident(s),
+        Var(ref s) => ident(s.as_str()),
         Principal => str("IDL.Principal"),
         Opt(ref t) => str("IDL.Opt").append(enclose("(", pp_ty(t), ")")),
         Vec(ref t) => str("IDL.Vec").append(enclose("(", pp_ty(t), ")")),
         Record(ref fs) => {
             if is_tuple(ty) {
-                let tuple = concat(fs.iter().map(|f| pp_ty(&f.ty)), ",");
-                str("IDL.Tuple").append(enclose("(", tuple, ")"))
+                let fs = fs.iter().map(|f| pp_ty(&f.ty));
+                str("IDL.Tuple").append(sep_enclose(fs, ",", "(", ")"))
             } else {
                 str("IDL.Record").append(pp_fields(fs))
             }
@@ -156,69 +156,75 @@ fn pp_field(field: &Field) -> RcDoc<'_> {
 }
 
 fn pp_fields(fs: &[Field]) -> RcDoc<'_> {
-    let fields = concat(fs.iter().map(pp_field), ",");
-    enclose_space("({", fields, "})")
+    sep_enclose_space(fs.iter().map(pp_field), ",", "({", "})")
 }
 
 fn pp_function(func: &Function) -> RcDoc<'_> {
     let args = pp_args(&func.args);
-    let rets = pp_rets(&func.rets);
+    let rets = pp_args(&func.rets);
     let modes = pp_modes(&func.modes);
-    let doc = concat([args, rets, modes].into_iter(), ",");
-    enclose("(", doc, ")").nest(INDENT_SPACE)
+    sep_enclose([args, rets, modes], ",", "(", ")").nest(INDENT_SPACE)
 }
 
-fn pp_args(args: &[Type]) -> RcDoc<'_> {
-    let doc = concat(args.iter().map(pp_ty), ",");
-    enclose("[", doc, "]")
+fn pp_args(args: &[ArgType]) -> RcDoc<'_> {
+    pp_types(args.iter().map(|arg| &arg.typ))
 }
 
-fn pp_rets(args: &[Type]) -> RcDoc<'_> {
-    pp_args(args)
+fn pp_types<'a, T>(types: T) -> RcDoc<'a>
+where
+    T: Iterator<Item = &'a Type>,
+{
+    sep_enclose(types.map(pp_ty), ",", "[", "]")
 }
 
 fn pp_modes(modes: &[candid::types::FuncMode]) -> RcDoc<'_> {
-    let doc = concat(
-        modes
-            .iter()
-            .map(|m| str("'").append(pp_mode(m)).append("'")),
-        ",",
-    );
-    enclose("[", doc, "]")
+    let ms = modes
+        .iter()
+        .map(|m| str("'").append(pp_mode(m)).append("'"));
+    sep_enclose(ms, ",", "[", "]")
 }
 
 fn pp_service(serv: &[(String, Type)]) -> RcDoc<'_> {
-    let doc = concat(
-        serv.iter()
-            .map(|(id, func)| quote_ident(id).append(kwd(":")).append(pp_ty(func))),
-        ",",
-    );
-    enclose_space("({", doc, "})")
+    let ms = serv
+        .iter()
+        .map(|(id, func)| quote_ident(id).append(kwd(":")).append(pp_ty(func)));
+    sep_enclose_space(ms, ",", "({", "})")
 }
 
 fn pp_defs<'a>(
     env: &'a TypeEnv,
     def_list: &'a [&'a str],
     recs: &'a BTreeSet<&'a str>,
+    export: bool,
 ) -> RcDoc<'a> {
-    let recs_doc = lines(
-        recs.iter()
-            .map(|id| kwd("const").append(ident(id)).append(" = IDL.Rec();")),
-    );
-    let defs = lines(def_list.iter().map(|id| {
-        let ty = env.find_type(id).unwrap();
+    let export_prefix = if export { str("export ") } else { RcDoc::nil() };
+
+    let recs_doc = lines(recs.iter().map(|id| {
+        export_prefix
+            .clone()
+            .append(kwd("const"))
+            .append(ident(id))
+            .append(" = IDL.Rec();")
+    }));
+    let mut defs = lines(def_list.iter().map(|&id| {
+        let ty = env.find_type(&id.into()).unwrap();
         if recs.contains(id) {
             ident(id)
                 .append(".fill")
                 .append(enclose("(", pp_ty(ty), ");"))
         } else {
-            kwd("const")
+            export_prefix
+                .clone()
+                .append(kwd("const"))
                 .append(ident(id))
                 .append(" = ")
                 .append(pp_ty(ty))
                 .append(";")
         }
     }));
+    if !def_list.is_empty() {
+        defs = defs.append(RcDoc::hardline())
+    }
     recs_doc.append(defs)
 }
 
@@ -226,10 +232,10 @@ fn pp_actor<'a>(ty: &'a Type, recs: &'a BTreeSet<&'a str>) -> RcDoc<'a> {
     match ty.as_ref() {
         TypeInner::Service(_) => pp_ty(ty),
         TypeInner::Var(id) => {
-            if recs.contains(&*id.clone()) {
-                str(id).append(".getType()")
+            if recs.contains(id.as_str()) {
+                str(id.as_str()).append(".getType()")
             } else {
-                str(id)
+                str(id.as_str())
             }
         }
         TypeInner::Class(_, t) => pp_actor(t, recs),
@@ -237,38 +243,73 @@ fn pp_actor<'a>(ty: &'a Type, recs: &'a BTreeSet<&'a str>) -> RcDoc<'a> {
     }
 }
 
+fn pp_imports<'a>() -> RcDoc<'a> {
+    str("import { IDL } from '@dfinity/candid';")
+        .append(RcDoc::hardline())
+        .append(RcDoc::hardline())
+}
+
 pub fn compile(env: &TypeEnv, actor: &Option<Type>) -> String {
     match actor {
         None => {
-            let def_list: Vec<_> = env.0.iter().map(|pair| pair.0.as_ref()).collect();
+            let def_list: Vec<_> = env.to_sorted_iter().map(|pair| pair.0.as_str()).collect();
             let recs = infer_rec(env, &def_list).unwrap();
-            let doc = pp_defs(env, &def_list, &recs);
-            doc.pretty(LINE_WIDTH).to_string()
+            let doc = pp_defs(env, &def_list, &recs, true);
+            let result = pp_imports().append(doc).pretty(LINE_WIDTH).to_string();
+
+            result
         }
         Some(actor) => {
             let def_list = chase_actor(env, actor).unwrap();
             let recs = infer_rec(env, &def_list).unwrap();
-            let defs = pp_defs(env, &def_list, &recs);
-            let init = if let TypeInner::Class(ref args, _) = actor.as_ref() {
-                args.as_slice()
+            let types = if let TypeInner::Class(ref args, _) = actor.as_ref() {
+                args.iter().map(|arg| arg.typ.clone()).collect::<Vec<_>>()
             } else {
-                &[][..]
+                Vec::new()
             };
-            let actor = kwd("return").append(pp_actor(actor, &recs)).append(";");
-            let body = defs.append(actor);
-            let doc = str("export const idlFactory = ({ IDL }) => ")
-                .append(enclose_space("{", body, "};"));
-            // export init args
-            let init_defs = chase_types(env, init).unwrap();
+            let init_types = types.as_slice();
+
+            let defs = pp_defs(env, &def_list, &recs, true);
+            let actor = pp_actor(actor, &recs);
+
+            let idl_service = str("export const idlService = ")
+                .append(actor.clone())
+                .append(";");
+
+            let idl_init_args = str("export const idlInitArgs = ")
+                .append(pp_types(init_types.iter()))
+                .append(";");
+
+            let idl_factory_return = kwd("return").append(actor).append(";");
+            let idl_factory_body = pp_defs(env, &def_list, &recs, false).append(idl_factory_return);
+            let idl_factory_doc = str("export const idlFactory = ({ IDL }) => ")
+                .append(enclose_space("{", idl_factory_body, "};"));
+
+            let init_defs = chase_types(env, init_types).unwrap();
             let init_recs = infer_rec(env, &init_defs).unwrap();
-            let init_defs_doc = pp_defs(env, &init_defs, &init_recs);
-            let init_doc = kwd("return").append(pp_rets(init)).append(";");
+            let init_defs_doc = pp_defs(env, &init_defs, &init_recs, false);
+            let init_doc = kwd("return")
+                .append(pp_types(init_types.iter()))
+                .append(";");
             let init_doc = init_defs_doc.append(init_doc);
             let init_doc =
                 str("export const init = ({ IDL }) => ").append(enclose_space("{", init_doc, "};"));
             let init_doc = init_doc.pretty(LINE_WIDTH).to_string();
-            let doc = doc.append(RcDoc::hardline()).append(init_doc);
-            doc.pretty(LINE_WIDTH).to_string()
+
+            let result = pp_imports()
+                .append(defs)
+                .append(idl_service)
+                .append(RcDoc::hardline())
+                .append(RcDoc::hardline())
+                .append(idl_init_args)
+                .append(RcDoc::hardline())
+                .append(RcDoc::hardline())
+                .append(idl_factory_doc)
+                .append(RcDoc::hardline())
+                .append(RcDoc::hardline())
+                .append(init_doc);
+
+            result.pretty(LINE_WIDTH).to_string()
         }
     }
 }
@@ -311,10 +352,6 @@ pub mod value {
             .append(pp_value(&field.val))
     }
 
-    fn pp_fields(fields: &[IDLField]) -> RcDoc<'_> {
-        concat(fields.iter().map(pp_field), ",")
-    }
-
     pub fn pp_value(v: &IDLValue) -> RcDoc<'_> {
         use IDLValue::*;
         match v {
@@ -340,20 +377,13 @@ pub mod value {
             Text(s) => RcDoc::text(format!("'{}'", s.escape_debug())),
             None => RcDoc::text("[]"),
             Opt(v) => enclose_space("[", pp_value(v), "]"),
-            Blob(blob) => {
-                let body = concat(blob.iter().map(RcDoc::as_string), ",");
-                enclose_space("[", body, "]")
-            }
-            Vec(vs) => {
-                let body = concat(vs.iter().map(pp_value), ",");
-                enclose_space("[", body, "]")
-            }
+            Blob(blob) => sep_enclose_space(blob.iter().map(RcDoc::as_string), ",", "[", "]"),
+            Vec(vs) => sep_enclose_space(vs.iter().map(pp_value), ",", "[", "]"),
             Record(fields) => {
                 if is_tuple(v) {
-                    let tuple = concat(fields.iter().map(|f| pp_value(&f.val)), ",");
-                    enclose_space("[", tuple, "]")
+                    sep_enclose_space(fields.iter().map(|f| pp_value(&f.val)), ",", "[", "]")
                 } else {
-                    enclose_space("{", pp_fields(fields), "}")
+                    sep_enclose_space(fields.iter().map(pp_field), ",", "{", "}")
                 }
             }
             Variant(v) => enclose_space("{", pp_field(&v.0), "}"),
@@ -361,7 +391,6 @@ pub mod value {
     }
 
     pub fn pp_args(args: &IDLArgs) -> RcDoc<'_> {
-        let body = concat(args.args.iter().map(pp_value), ",");
-        enclose("[", body, "]")
+        sep_enclose(args.args.iter().map(pp_value), ",", "[", "]")
     }
 }
diff --git a/rust/candid_parser/src/bindings/motoko.rs b/rust/candid_parser/src/bindings/motoko.rs
index 326b7fc61..500f5baed 100644
--- a/rust/candid_parser/src/bindings/motoko.rs
+++ b/rust/candid_parser/src/bindings/motoko.rs
@@ -4,7 +4,7 @@
 use crate::syntax::{self, IDLActorType, IDLMergedProg, IDLType};
 use candid::pretty::candid::is_valid_as_id;
 use candid::pretty::utils::*;
-use candid::types::{Field, FuncMode, Function, Label, SharedLabel, Type, TypeInner};
+use candid::types::{ArgType, Field, FuncMode, Function, Label, SharedLabel, Type, TypeInner};
 use candid::TypeEnv;
 use pretty::RcDoc;
 
@@ -138,7 +138,7 @@ fn pp_ty(ty: &Type) -> RcDoc<'_> {
         Text => str("Text"),
         Reserved => str("Any"),
         Empty => str("None"),
-        Var(ref s) => escape(s, false),
+        Var(ref s) => escape(s.as_str(), false),
         Principal => str("Principal"),
         Opt(ref t) => str("?").append(pp_ty(t)),
         Vec(ref t) => pp_vec(t, None),
@@ -185,24 +185,45 @@ fn pp_function(func: &Function) -> RcDoc<'_> {
     }
     .nest(INDENT_SPACE)
 }
-fn pp_args(args: &[Type]) -> RcDoc<'_> {
+fn pp_args(args: &[ArgType]) -> RcDoc<'_> {
     match args {
         [ty] => {
-            if is_tuple(ty) {
-                enclose("(", pp_ty(ty), ")")
+            let typ = if is_tuple(&ty.typ) {
+                enclose("(", pp_ty(&ty.typ), ")")
             } else {
-                pp_ty(ty)
+                pp_ty(&ty.typ)
+            };
+            if let Some(name) = &ty.name {
+                enclose("(", escape(name, false).append(" : ").append(typ), ")")
+            } else {
+                typ
             }
         }
         _ => {
-            let doc = concat(args.iter().map(pp_ty), ",");
-            enclose("(", doc, ")")
+            let args = args.iter().map(|arg| {
+                if let Some(name) = &arg.name {
+                    escape(name, false).append(" : ").append(pp_ty(&arg.typ))
+                } else {
+                    pp_ty(&arg.typ)
+                }
+            });
+            sep_enclose(args, ",", "(", ")")
         }
     }
 }
 
-fn pp_rets(args: &[Type]) -> RcDoc<'_> {
-    pp_args(args)
+fn pp_rets(rets: &[ArgType]) -> RcDoc<'_> {
+    match rets {
+        [ty] => {
+            let typ = &ty.typ;
+            if is_tuple(typ) {
+                enclose("(", pp_ty(typ), ")")
+            } else {
+                pp_ty(typ)
+            }
+        }
+        _ => sep_enclose(rets.iter().map(|ret| pp_ty(&ret.typ)), ",", "(", ")"),
+    }
 }
 
 fn pp_service<'a>(serv: &'a [(String, Type)], syntax: Option<&'a [syntax::Binding]>) -> RcDoc<'a> {
@@ -219,12 +240,11 @@ fn pp_service<'a>(serv: &'a [(String, Type)], syntax: Option<&'a [syntax::Bindin
             .append(" : ")
             .append(pp_ty_rich(func, syntax_field_ty))
     });
-    kwd("actor").append(enclose_space("{", concat(methods, ";"), "}"))
+    kwd("actor").append(sep_enclose_space(methods, ";", "{", "}"))
 }
 
 fn pp_tuple<'a>(fields: &'a [Field]) -> RcDoc<'a> {
-    let tuple = concat(fields.iter().map(|f| pp_ty(&f.ty)), ",");
-    enclose("(", tuple, ")")
+    sep_enclose(fields.iter().map(|f| pp_ty(&f.ty)), ",", "(", ")")
 }
 
 fn pp_vec<'a>(inner: &'a Type, syntax: Option<&'a IDLType>) -> RcDoc<'a> {
@@ -260,7 +280,7 @@ fn pp_record<'a>(fields: &'a [Field], syntax: Option<&'a [syntax::TypeField]>) -
             .append(" : ")
             .append(pp_ty_rich(&field.ty, syntax_field))
     });
-    enclose_space("{", concat(fields, ";"), "}")
+    sep_enclose_space(fields, ";", "{", "}")
 }
 
 fn pp_variant<'a>(fields: &'a [Field], syntax: Option<&'a [syntax::TypeField]>) -> RcDoc<'a> {
@@ -277,10 +297,10 @@ fn pp_variant<'a>(fields: &'a [Field], syntax: Option<&'a [syntax::TypeField]>)
             doc
         }
     });
-    enclose_space("{", concat(fields, ";"), "}")
+    sep_enclose_space(fields, ";", "{", "}")
 }
 
-fn pp_class<'a>((args, ty): (&'a [Type], &'a Type), syntax: Option<&'a IDLType>) -> RcDoc<'a> {
+fn pp_class<'a>((args, ty): (&'a [ArgType], &'a Type), syntax: Option<&'a IDLType>) -> RcDoc<'a> {
     let doc = pp_args(args).append(" -> async ");
     match ty.as_ref() {
         TypeInner::Service(_) => doc.append(pp_ty_rich(ty, syntax)),
@@ -295,12 +315,12 @@ fn pp_docs<'a>(docs: &'a [String]) -> RcDoc<'a> {
 
 fn pp_defs<'a>(env: &'a TypeEnv, prog: &'a IDLMergedProg) -> RcDoc<'a> {
     lines(env.0.iter().map(|(id, ty)| {
-        let syntax = prog.lookup(id);
+        let syntax = prog.lookup(id.as_str());
         let docs = syntax
             .map(|b| pp_docs(b.docs.as_ref()))
             .unwrap_or(RcDoc::nil());
         docs.append(kwd("public type"))
-            .append(escape(id, false))
+            .append(escape(id.as_str(), false))
             .append(" = ")
             .append(pp_ty_rich(ty, syntax.map(|b| &b.typ)))
             .append(";")
diff --git a/rust/candid_parser/src/bindings/rust.rs b/rust/candid_parser/src/bindings/rust.rs
index ef1439dab..5cae7fd1c 100644
--- a/rust/candid_parser/src/bindings/rust.rs
+++ b/rust/candid_parser/src/bindings/rust.rs
@@ -4,8 +4,10 @@ use crate::{
     syntax::{self, IDLActorType, IDLMergedProg, IDLType},
     Deserialize,
 };
-use candid::pretty::utils::*;
-use candid::types::{Field, Function, Label, SharedLabel, Type, TypeEnv, TypeInner};
+use candid::types::{
+    internal::TypeKey, Field, Function, Label, SharedLabel, Type, TypeEnv, TypeInner,
+};
+use candid::{pretty::utils::*, types::ArgType};
 use convert_case::{Case, Casing};
 use pretty::RcDoc;
 use serde::Serialize;
@@ -18,7 +20,7 @@ use identifier::{to_identifier_case, IdentifierCase};
 const DOC_COMMENT_PREFIX: &str = "/// ";
 
 /// Maps the names generated during nominalization to the original syntactic types.
-type GeneratedTypes<'a> = BTreeMap<String, &'a IDLType>;
+type GeneratedTypes<'a> = BTreeMap<TypeKey, &'a IDLType>;
 
 #[derive(Default, Deserialize, Clone, Debug)]
 pub struct BindingConfig {
@@ -212,9 +214,15 @@ impl<'a> State<'a> {
                 .map(|(k, v)| (k.clone(), v.clone()))
                 .collect(),
         );
-        let src = candid::pretty::candid::pp_init_args(&env, std::slice::from_ref(src))
-            .pretty(80)
-            .to_string();
+        let src = candid::pretty::candid::pp_named_init_args(
+            &env,
+            &[ArgType {
+                name: None,
+                typ: src.clone(),
+            }],
+        )
+        .pretty(80)
+        .to_string();
         let match_path = self.state.config_source.get("use_type").unwrap().join(".");
         let test_name = use_type.replace(|c: char| !c.is_ascii_alphanumeric(), "_");
         let body = format!(
@@ -259,7 +267,7 @@ fn test_{test_name}() {{
                 Text => str("String"),
                 Reserved => str("candid::Reserved"),
                 Empty => str("candid::Empty"),
-                Var(ref id) => self.pp_var(id, is_ref),
+                Var(ref id) => self.pp_var(id.as_str(), is_ref),
                 Principal => str("Principal"),
                 Opt(ref t) => self.pp_opt(t, is_ref),
                 // It's a bit tricky to use `deserialize_with = "serde_bytes"`. It's not working for `type t = blob`
@@ -354,11 +362,11 @@ fn test_{test_name}() {{
             } else {
                 RcDoc::nil()
             };
-            let res = vis.append(self.pp_ty(&f.ty, is_ref)).append(",");
+            let res = vis.append(self.pp_ty(&f.ty, is_ref));
             self.state.pop_state(old, StateElem::Label(&lab));
             res
         });
-        enclose("(", RcDoc::concat(tuple), ")")
+        sep_enclose(tuple, ",", "(", ")")
     }
 
     fn pp_record_field<'b>(&mut self, field: &'b Field, need_vis: bool, is_ref: bool) -> RcDoc<'b> {
@@ -395,8 +403,7 @@ fn test_{test_name}() {{
                     docs.append(self.pp_record_field(f, need_vis, is_ref))
                 })
                 .collect();
-            let fields = concat(fields.into_iter(), ",");
-            enclose_space("{", fields, "}")
+            sep_enclose_space(fields, ",", "{", "}")
         };
         if let Some(old) = old {
             self.state.pop_state(old, StateElem::TypeStr("record"));
@@ -459,20 +466,21 @@ fn test_{test_name}() {{
             let (docs, syntax_field) = find_field(syntax, &f.id);
             docs.append(self.pp_variant_field(f, syntax_field))
         });
-        let res = enclose_space("{", concat(fields, ","), "}");
+        let res = sep_enclose_space(fields, ",", "{", "}");
         self.state.pop_state(old, StateElem::TypeStr("variant"));
         res
     }
 
     fn pp_defs(&mut self, def_list: &'a [&'a str]) -> RcDoc<'a> {
         let mut res = Vec::with_capacity(def_list.len());
-        for id in def_list {
+        for &id in def_list {
             let old = self.state.push_state(&StateElem::Label(id));
             if self.state.config.use_type.is_some() {
                 self.state.pop_state(old, StateElem::Label(id));
                 continue;
             }
-            let ty = self.state.env.find_type(id).unwrap();
+            let type_key: TypeKey = id.into();
+            let ty = self.state.env.find_type(&type_key).unwrap();
             let name = self
                 .state
                 .config
@@ -483,7 +491,7 @@ fn test_{test_name}() {{
             let syntax = self.prog.lookup(id);
             let syntax_ty = syntax
                 .map(|b| &b.typ)
-                .or_else(|| self.generated_types.get(*id).map(|t| &**t));
+                .or_else(|| self.generated_types.get(&type_key).map(|t| &**t));
             let docs = syntax
                 .map(|b| pp_docs(b.docs.as_ref()))
                 .unwrap_or(RcDoc::nil());
@@ -569,24 +577,31 @@ fn test_{test_name}() {{
         }
         lines(res.into_iter())
     }
-    fn pp_args<'b>(&mut self, args: &'b [Type], prefix: &'b str) -> RcDoc<'b> {
-        let tys = args.iter().enumerate().map(|(i, t)| {
-            let lab = format!("{prefix}{i}");
+    fn pp_args<'b>(&mut self, args: &'b [ArgType], prefix: &'b str) -> RcDoc<'b> {
+        let args = args.iter().enumerate().map(|(i, t)| {
+            let lab = t.name.clone().unwrap_or_else(|| format!("{prefix}{i}"));
             let old = self.state.push_state(&StateElem::Label(&lab));
-            let res = self.pp_ty(t, true);
+            let res = self.pp_ty(&t.typ, true);
             self.state.pop_state(old, StateElem::Label(&lab));
             res
         });
-        enclose("(", concat(tys.into_iter(), ","), ")")
+        sep_enclose(args, ",", "(", ")")
     }
-    fn pp_rets<'b>(&mut self, rets: &'b [Type]) -> RcDoc<'b> {
-        self.pp_args(rets, "ret")
+    fn pp_rets<'b>(&mut self, rets: &'b [ArgType], prefix: &'b str) -> RcDoc<'b> {
+        let tys = rets.iter().enumerate().map(|(i, t)| {
+            let lab = format!("{prefix}{i}");
+            let old = self.state.push_state(&StateElem::Label(&lab));
+            let res = self.pp_ty(&t.typ, true);
+            self.state.pop_state(old, StateElem::Label(&lab));
+            res
+        });
+        sep_enclose(tys, ",", "(", ")")
     }
     fn pp_ty_func<'b>(&mut self, f: &'b Function) -> RcDoc<'b> {
         let lab = StateElem::TypeStr("func");
         let old = self.state.push_state(&lab);
         let args = self.pp_args(&f.args, "arg");
-        let rets = self.pp_rets(&f.rets);
+        let rets = self.pp_rets(&f.rets, "ret");
         let modes = candid::pretty::candid::pp_modes(&f.modes);
         let res = args
             .append(" ->")
@@ -611,7 +626,7 @@ fn test_{test_name}() {{
                 .append(kwd("\" :"))
                 .append(func_doc)
         });
-        let res = enclose_space("{", concat(methods, ";"), "}");
+        let res = sep_enclose_space(methods, ";", "{", "}");
         self.state.pop_state(old, lab);
         res
     }
@@ -636,7 +651,7 @@ fn test_{test_name}() {{
             .iter()
             .enumerate()
             .map(|(i, arg)| {
-                let lab = format!("arg{i}");
+                let lab = arg.name.clone().unwrap_or_else(|| format!("arg{i}"));
                 let old = self.state.push_state(&StateElem::Label(&lab));
                 let name = self
                     .state
@@ -645,7 +660,7 @@ fn test_{test_name}() {{
                     .clone()
                     .unwrap_or_else(|| lab.clone());
                 self.state.update_stats("name");
-                let res = self.pp_ty(arg, true);
+                let res = self.pp_ty(&arg.typ, true);
                 self.state.pop_state(old, StateElem::Label(&lab));
                 (name, res)
             })
@@ -654,10 +669,10 @@ fn test_{test_name}() {{
             .rets
             .iter()
             .enumerate()
-            .map(|(i, ty)| {
+            .map(|(i, ret)| {
                 let lab = format!("ret{i}");
                 let old = self.state.push_state(&StateElem::Label(&lab));
-                let res = self.pp_ty(ty, true);
+                let res = self.pp_ty(&ret.typ, true);
                 self.state.pop_state(old, StateElem::Label(&lab));
                 res
             })
@@ -695,7 +710,7 @@ fn test_{test_name}() {{
                 .iter()
                 .enumerate()
                 .map(|(i, arg)| {
-                    let lab = format!("arg{i}");
+                    let lab = arg.name.clone().unwrap_or_else(|| format!("arg{i}"));
                     let old = self.state.push_state(&StateElem::Label(&lab));
                     let name = self
                         .state
@@ -704,7 +719,7 @@ fn test_{test_name}() {{
                         .clone()
                         .unwrap_or_else(|| lab.clone());
                     self.state.update_stats("name");
-                    let res = self.pp_ty(arg, true);
+                    let res = self.pp_ty(&arg.typ, true);
                     self.state.pop_state(old, StateElem::Label(&lab));
                     (name, res.pretty(LINE_WIDTH).to_string())
                 })
@@ -763,7 +778,9 @@ pub fn emit_bindgen(
     let def_list = if let Some(actor) = &actor {
         chase_actor(&env, actor).unwrap()
     } else {
-        env.0.iter().map(|pair| pair.0.as_ref()).collect::<Vec<_>>()
+        env.to_sorted_iter()
+            .map(|pair| pair.0.as_str())
+            .collect::<Vec<_>>()
     };
     let recs = infer_rec(&env, &def_list).unwrap();
     let mut state = State {
@@ -981,6 +998,7 @@ impl<'b> NominalState<'_, 'b> {
                         &TypeInner::Record(fs.to_vec()).into(),
                         syntax,
                     );
+                    let new_var: TypeKey = new_var.into();
                     env.0.insert(new_var.clone(), ty);
                     if let Some(syntax) = syntax {
                         self.generated_types.insert(new_var.clone(), syntax);
@@ -1026,6 +1044,7 @@ impl<'b> NominalState<'_, 'b> {
                         &TypeInner::Variant(fs.to_vec()).into(),
                         syntax,
                     );
+                    let new_var: TypeKey = new_var.into();
                     env.0.insert(new_var.clone(), ty);
                     if let Some(syntax) = syntax {
                         self.generated_types.insert(new_var.clone(), syntax);
@@ -1043,7 +1062,7 @@ impl<'b> NominalState<'_, 'b> {
                             .into_iter()
                             .enumerate()
                             .map(|(i, arg)| {
-                                let lab = format!("arg{i}");
+                                let lab = arg.name.clone().unwrap_or_else(|| format!("arg{i}"));
                                 let old = self.state.push_state(&StateElem::Label(&lab));
                                 let idx = if i == 0 {
                                     "".to_string()
@@ -1051,17 +1070,20 @@ impl<'b> NominalState<'_, 'b> {
                                     i.to_string()
                                 };
                                 path.push(TypePath::Func(format!("arg{idx}")));
-                                let ty = self.nominalize(env, path, &arg, None);
+                                let ty = self.nominalize(env, path, &arg.typ, None);
                                 path.pop();
                                 self.state.pop_state(old, StateElem::Label(&lab));
-                                ty
+                                ArgType {
+                                    name: arg.name.clone(),
+                                    typ: ty,
+                                }
                             })
                             .collect(),
                         rets: func
                             .rets
                             .into_iter()
                             .enumerate()
-                            .map(|(i, ty)| {
+                            .map(|(i, ret)| {
                                 let lab = format!("ret{i}");
                                 let old = self.state.push_state(&StateElem::Label(&lab));
                                 let idx = if i == 0 {
@@ -1070,10 +1092,13 @@ impl<'b> NominalState<'_, 'b> {
                                     i.to_string()
                                 };
                                 path.push(TypePath::Func(format!("ret{idx}")));
-                                let ty = self.nominalize(env, path, &ty, None);
+                                let ty = self.nominalize(env, path, &ret.typ, None);
                                 path.pop();
                                 self.state.pop_state(old, StateElem::Label(&lab));
-                                ty
+                                ArgType {
+                                    name: ret.name.clone(),
+                                    typ: ty,
+                                }
                             })
                             .collect(),
                     })
@@ -1092,8 +1117,8 @@ impl<'b> NominalState<'_, 'b> {
                         &TypeInner::Func(func.clone()).into(),
                         None,
                     );
-                    env.0.insert(new_var.clone(), ty);
-                    TypeInner::Var(new_var)
+                    env.0.insert(new_var.clone().into(), ty);
+                    TypeInner::Var(new_var.into())
                 }
             },
             TypeInner::Service(serv) => match path.last() {
@@ -1124,8 +1149,8 @@ impl<'b> NominalState<'_, 'b> {
                         &TypeInner::Service(serv.clone()).into(),
                         None,
                     );
-                    env.0.insert(new_var.clone(), ty);
-                    TypeInner::Var(new_var)
+                    env.0.insert(new_var.clone().into(), ty);
+                    TypeInner::Var(new_var.into())
                 }
             },
             TypeInner::Class(args, ty) => {
@@ -1140,10 +1165,13 @@ impl<'b> NominalState<'_, 'b> {
                             let elem = StateElem::Label("init");
                             let old = self.state.push_state(&elem);
                             path.push(TypePath::Init);
-                            let ty = self.nominalize(env, path, arg, None);
+                            let ty = self.nominalize(env, path, &arg.typ, None);
                             path.pop();
                             self.state.pop_state(old, elem);
-                            ty
+                            ArgType {
+                                name: arg.name.clone(),
+                                typ: ty,
+                            }
                         })
                         .collect(),
                     self.nominalize(env, path, ty, syntax_ty),
@@ -1164,12 +1192,17 @@ impl<'b> NominalState<'_, 'b> {
         prog: &'b IDLMergedProg,
     ) -> (TypeEnv, Option<Type>) {
         let mut res = TypeEnv(Default::default());
-        for (id, ty) in self.state.env.0.iter() {
-            let elem = StateElem::Label(id);
+        for (id, ty) in self.state.env.to_sorted_iter() {
+            let elem = StateElem::Label(id.as_str());
             let old = self.state.push_state(&elem);
-            let syntax = prog.lookup(id).map(|t| &t.typ);
-            let ty = self.nominalize(&mut res, &mut vec![TypePath::Id(id.clone())], ty, syntax);
-            res.0.insert(id.to_string(), ty);
+            let syntax = prog.lookup(id.as_str()).map(|t| &t.typ);
+            let ty = self.nominalize(
+                &mut res,
+                &mut vec![TypePath::Id(id.to_string())],
+                ty,
+                syntax,
+            );
+            res.0.insert(id.clone(), ty);
             self.state.pop_state(old, elem);
         }
         let actor = actor
diff --git a/rust/candid_parser/src/bindings/typescript.rs b/rust/candid_parser/src/bindings/typescript.rs
index 673d80488..5fe2e4ca1 100644
--- a/rust/candid_parser/src/bindings/typescript.rs
+++ b/rust/candid_parser/src/bindings/typescript.rs
@@ -77,7 +77,7 @@ fn pp_ty<'a>(env: &'a TypeEnv, ty: &'a Type, is_ref: bool) -> RcDoc<'a> {
             if is_ref && matches!(ty.as_ref(), Service(_)) {
                 return pp_inline_service();
             }
-            ident(id)
+            ident(id.as_str())
         }
         Principal => str("Principal"),
         Opt(ref t) => pp_opt(env, t, None, is_ref),
@@ -161,17 +161,14 @@ fn pp_record<'a>(
     is_ref: bool,
 ) -> RcDoc<'a> {
     if is_tuple_fields(fields) {
-        let tuple = concat(fields.iter().map(|f| pp_ty(env, &f.ty, is_ref)), ",");
-        enclose("[", tuple, "]")
+        let fs = fields.iter().map(|f| pp_ty(env, &f.ty, is_ref));
+        sep_enclose(fs, ",", "[", "]")
     } else {
-        let fields = concat(
-            fields.iter().map(|f| {
-                let (docs, syntax_field) = find_field(syntax, &f.id);
-                docs.append(pp_field(env, f, syntax_field, is_ref))
-            }),
-            ",",
-        );
-        enclose_space("{", fields, "}")
+        let fields = fields.iter().map(|f| {
+            let (docs, syntax_field) = find_field(syntax, &f.id);
+            docs.append(pp_field(env, f, syntax_field, is_ref))
+        });
+        sep_enclose_space(fields, ",", "{", "}")
     }
 }
 
@@ -206,14 +203,15 @@ fn pp_opt<'a>(
 }
 
 fn pp_function<'a>(env: &'a TypeEnv, func: &'a Function) -> RcDoc<'a> {
-    let args = func.args.iter().map(|arg| pp_ty(env, arg, true));
-    let args = enclose("[", concat(args, ","), "]");
+    let args = func.args.iter().map(|arg| pp_ty(env, &arg.typ, true));
+    let args = sep_enclose(args, ",", "[", "]");
     let rets = match func.rets.len() {
         0 => str("undefined"),
-        1 => pp_ty(env, &func.rets[0], true),
-        _ => enclose(
+        1 => pp_ty(env, &func.rets[0].typ, true),
+        _ => sep_enclose(
+            func.rets.iter().map(|ty| pp_ty(env, &ty.typ, true)),
+            ",",
             "[",
-            concat(func.rets.iter().map(|ty| pp_ty(env, ty, true)), ","),
             "]",
         ),
     };
@@ -238,12 +236,12 @@ fn pp_service<'a>(
         }
         let func = match func.as_ref() {
             TypeInner::Func(ref func) => pp_function(env, func),
-            TypeInner::Var(ref id) => ident(id),
+            TypeInner::Var(ref id) => ident(id.as_str()),
             _ => unreachable!(),
         };
         docs.append(quote_ident(id)).append(kwd(":")).append(func)
     });
-    enclose_space("{", concat(methods, ","), "}")
+    sep_enclose_space(methods, ",", "{", "}")
 }
 
 /// Escapes doc comment content to prevent comment injection attacks.
@@ -268,8 +266,8 @@ fn pp_docs<'a>(docs: &'a [String]) -> RcDoc<'a> {
 }
 
 fn pp_defs<'a>(env: &'a TypeEnv, def_list: &'a [&'a str], prog: &'a IDLMergedProg) -> RcDoc<'a> {
-    lines(def_list.iter().map(|id| {
-        let ty = env.find_type(id).unwrap();
+    lines(def_list.iter().map(|&id| {
+        let ty = env.find_type(&id.into()).unwrap();
         let syntax = prog.lookup(id);
         let syntax_ty = syntax.map(|s| &s.typ);
         let docs = syntax
@@ -292,7 +290,7 @@ fn pp_defs<'a>(env: &'a TypeEnv, def_list: &'a [&'a str], prog: &'a IDLMergedPro
             TypeInner::Var(ref inner_id) => kwd("export type")
                 .append(ident(id))
                 .append(" = ")
-                .append(ident(inner_id))
+                .append(ident(inner_id.as_str()))
                 .append(";"),
             _ => kwd("export type")
                 .append(ident(id))
@@ -310,7 +308,7 @@ fn pp_actor<'a>(env: &'a TypeEnv, ty: &'a Type, syntax: Option<&'a IDLType>) ->
         TypeInner::Service(_) => service_doc.append(pp_ty_rich(env, ty, syntax, false)),
         TypeInner::Var(id) => service_doc
             .append(kwd("extends"))
-            .append(str(id))
+            .append(str(id.as_str()))
             .append(str(" {}")),
         TypeInner::Class(_, t) => {
             if let Some(IDLType::ClassT(_, syntax_t)) = syntax {
@@ -329,7 +327,7 @@ import type { ActorMethod } from '@icp-sdk/core/agent';
 import type { IDL } from '@icp-sdk/core/candid';
 "#;
     let syntax_actor = prog.resolve_actor().ok().flatten();
-    let def_list: Vec<_> = env.0.iter().map(|pair| pair.0.as_ref()).collect();
+    let def_list: Vec<_> = env.to_sorted_iter().map(|pair| pair.0.as_str()).collect();
     let defs = pp_defs(env, &def_list, prog);
     let actor = match actor {
         None => RcDoc::nil(),
@@ -339,6 +337,10 @@ import type { IDL } from '@icp-sdk/core/candid';
                 .map(|s| pp_docs(s.docs.as_ref()))
                 .unwrap_or(RcDoc::nil());
             docs.append(pp_actor(env, actor, syntax_actor.as_ref().map(|s| &s.typ)))
+                .append(RcDoc::line())
+                .append("export declare const idlService: IDL.ServiceClass;")
+                .append(RcDoc::line())
+                .append("export declare const idlInitArgs: IDL.Type[];")
                 .append(RcDoc::line())
                 .append("export declare const idlFactory: IDL.InterfaceFactory;")
                 .append(RcDoc::line())
diff --git a/rust/candid_parser/src/configs.rs b/rust/candid_parser/src/configs.rs
index 4b6a57cde..e50d80a19 100644
--- a/rust/candid_parser/src/configs.rs
+++ b/rust/candid_parser/src/configs.rs
@@ -393,7 +393,7 @@ fn path_name(t: &Type) -> String {
         TypeInner::Text => "text",
         TypeInner::Reserved => "reserved",
         TypeInner::Empty => "empty",
-        TypeInner::Var(id) => id,
+        TypeInner::Var(id) => id.as_str(),
         TypeInner::Knot(id) => id.name,
         TypeInner::Principal => "principal",
         TypeInner::Opt(_) => "opt",
diff --git a/rust/candid_parser/src/grammar.lalrpop b/rust/candid_parser/src/grammar.lalrpop
index 584be1729..dea382f75 100644
--- a/rust/candid_parser/src/grammar.lalrpop
+++ b/rust/candid_parser/src/grammar.lalrpop
@@ -1,7 +1,7 @@
 use super::test::{Assert, Input, Test};
-use super::token::{Token, error2, LexicalError, Span, TriviaMap};
+use super::token::{Token, error, error2, LexicalError, Span, TriviaMap};
 use candid::{Principal, types::Label};
-use crate::syntax::{IDLType, PrimType, TypeField, FuncType, Binding, Dec, IDLProg, IDLTypes, IDLInitArgs, IDLActorType};
+use crate::syntax::{IDLType, PrimType, TypeField, FuncType, Binding, Dec, IDLProg, IDLTypes, IDLInitArgs, IDLArgType, IDLActorType};
 use candid::types::value::{IDLField, IDLValue, IDLArgs, VariantValue};
 use candid::types::{TypeEnv, FuncMode};
 use candid::utils::check_unique;
@@ -217,16 +217,22 @@ VariantFieldTyp: TypeField = {
     <doc_comment:DocComment> <id:FieldId> =>? Ok(TypeField { label: Label::Id(id), typ: IDLType::PrimT(PrimType::Null), docs: doc_comment.unwrap_or_default() }),
 }
 
-TupTyp: Vec<IDLType> = "(" <SepBy<ArgTyp, ",">> ")" => <>;
+TupTyp: Vec<IDLArgType> = "(" <SepBy<ArgTyp, ",">> ")" =>? {
+    let args = <>;
+    let mut named_args: Vec<String> = args.iter().filter_map(|a| a.name.clone()).collect();
+    named_args.sort();
+    check_unique(named_args.iter()).map_err(|e| error(e))?;
+    Ok(args)
+};
 
 FuncTyp: FuncType = {
     <args:TupTyp> "->" <rets:TupTyp> <modes:FuncMode*> =>
         FuncType { modes, args, rets },
 }
 
-ArgTyp: IDLType = {
-    Typ => <>,
-    Name ":" <Typ> => <>,
+ArgTyp: IDLArgType = {
+    <t:Typ> => IDLArgType::new(t),
+    <n:Name> ":" <t:Typ> => IDLArgType::new_with_name(t, n),
 }
 
 FuncMode: FuncMode = {
diff --git a/rust/candid_parser/src/lib.rs b/rust/candid_parser/src/lib.rs
index 63d3674b4..bf579c8f4 100644
--- a/rust/candid_parser/src/lib.rs
+++ b/rust/candid_parser/src/lib.rs
@@ -69,7 +69,7 @@
 //!
 //! let method = env.get_method(&actor, "g").unwrap();
 //! assert_eq!(method.is_query(), true);
-//! assert_eq!(method.args, vec![TypeInner::Var("List".to_string()).into()]);
+//! assert_eq!(method.args.iter().map(|arg| arg.typ.clone()).collect::<Vec<_>>(), vec![TypeInner::Var("List".into()).into()]);
 //! # Ok(())
 //! # }
 //! ```
@@ -102,7 +102,7 @@
 //! let method = env.get_method(&actor, "f").unwrap();
 //! let args = parse_idl_args("(42, 42, 42, 42)")?;
 //! // Serialize arguments with candid types
-//! let encoded = args.to_bytes_with_types(&env, &method.args)?;
+//! let encoded = args.to_bytes_with_types(&env, &method.args.iter().map(|arg| arg.typ.clone()).collect::<Vec<_>>())?;
 //! let decoded = IDLArgs::from_bytes(&encoded)?;
 //! assert_eq!(decoded.args,
 //!        vec![IDLValue::Nat8(42),
diff --git a/rust/candid_parser/src/random.rs b/rust/candid_parser/src/random.rs
index 8a38e586d..31ca3bbdf 100644
--- a/rust/candid_parser/src/random.rs
+++ b/rust/candid_parser/src/random.rs
@@ -300,7 +300,7 @@ fn size_helper(env: &TypeEnv, seen: &mut HashSet<String>, t: &Type) -> Option<us
             if seen.insert(id.to_string()) {
                 let ty = env.rec_find_type(id).unwrap();
                 let res = size_helper(env, seen, ty)?;
-                seen.remove(id);
+                seen.remove(id.as_str());
                 res
             } else {
                 return None;
diff --git a/rust/candid_parser/src/syntax/mod.rs b/rust/candid_parser/src/syntax/mod.rs
index 8a9c51f33..f8caf3442 100644
--- a/rust/candid_parser/src/syntax/mod.rs
+++ b/rust/candid_parser/src/syntax/mod.rs
@@ -20,7 +20,7 @@ pub enum IDLType {
     RecordT(Vec<TypeField>),
     VariantT(Vec<TypeField>),
     ServT(Vec<Binding>),
-    ClassT(Vec<IDLType>, Box<IDLType>),
+    ClassT(Vec<IDLArgType>, Box<IDLType>),
     PrincipalT,
 }
 
@@ -51,7 +51,7 @@ impl std::str::FromStr for IDLType {
 
 #[derive(Debug, Clone)]
 pub struct IDLTypes {
-    pub args: Vec<IDLType>,
+    pub args: Vec<IDLArgType>,
 }
 
 impl std::str::FromStr for IDLTypes {
@@ -106,8 +106,32 @@ pub enum PrimType {
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct FuncType {
     pub modes: Vec<FuncMode>,
-    pub args: Vec<IDLType>,
-    pub rets: Vec<IDLType>,
+    pub args: Vec<IDLArgType>,
+    pub rets: Vec<IDLArgType>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct IDLArgType {
+    pub typ: IDLType,
+    pub name: Option<String>,
+}
+
+impl IDLArgType {
+    pub fn new(typ: IDLType) -> Self {
+        Self { typ, name: None }
+    }
+
+    /// Create a new IDLArgType with a name.
+    /// If the name is an `u32` number, we set it to None
+    /// as we don't want to use it as a arg name.
+    pub fn new_with_name(typ: IDLType, name: String) -> Self {
+        let name = if name.parse::<u32>().is_ok() {
+            None
+        } else {
+            Some(name)
+        };
+        Self { typ, name }
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -167,7 +191,7 @@ impl std::str::FromStr for IDLProg {
 #[derive(Debug)]
 pub struct IDLInitArgs {
     pub decs: Vec<Dec>,
-    pub args: Vec<IDLType>,
+    pub args: Vec<IDLArgType>,
 }
 
 impl std::str::FromStr for IDLInitArgs {
diff --git a/rust/candid_parser/src/syntax/pretty.rs b/rust/candid_parser/src/syntax/pretty.rs
index 1b1b1970e..8c89f7c1c 100644
--- a/rust/candid_parser/src/syntax/pretty.rs
+++ b/rust/candid_parser/src/syntax/pretty.rs
@@ -3,9 +3,11 @@ use pretty::RcDoc;
 use crate::{
     pretty::{
         candid::{pp_docs, pp_label_raw, pp_modes, pp_text},
-        utils::{concat, enclose, enclose_space, ident, kwd, lines, str, INDENT_SPACE, LINE_WIDTH},
+        utils::{ident, kwd, lines, sep_enclose, sep_enclose_space, str, INDENT_SPACE, LINE_WIDTH},
+    },
+    syntax::{
+        Binding, FuncType, IDLActorType, IDLArgType, IDLMergedProg, IDLType, PrimType, TypeField,
     },
-    syntax::{Binding, FuncType, IDLActorType, IDLMergedProg, IDLType, PrimType, TypeField},
 };
 
 fn pp_ty(ty: &IDLType) -> RcDoc<'_> {
@@ -52,7 +54,7 @@ fn pp_field(field: &TypeField, is_variant: bool) -> RcDoc<'_> {
 
 fn pp_fields(fs: &[TypeField], is_variant: bool) -> RcDoc<'_> {
     let fields = fs.iter().map(|f| pp_field(f, is_variant));
-    enclose_space("{", concat(fields, ";"), "}")
+    sep_enclose_space(fields, ";", "{", "}")
 }
 
 fn pp_opt(ty: &IDLType) -> RcDoc<'_> {
@@ -69,8 +71,8 @@ fn pp_vec(ty: &IDLType) -> RcDoc<'_> {
 
 fn pp_record(fs: &[TypeField], is_tuple: bool) -> RcDoc<'_> {
     if is_tuple {
-        let tuple = concat(fs.iter().map(|f| pp_ty(&f.typ)), ";");
-        kwd("record").append(enclose_space("{", tuple, "}"))
+        let fs = fs.iter().map(|f| pp_ty(&f.typ));
+        kwd("record").append(sep_enclose_space(fs, ";", "{", "}"))
     } else {
         kwd("record").append(pp_fields(fs, false))
     }
@@ -86,7 +88,7 @@ fn pp_function(func: &FuncType) -> RcDoc<'_> {
 
 fn pp_method(func: &FuncType) -> RcDoc<'_> {
     let args = pp_args(&func.args);
-    let rets = pp_rets(&func.rets);
+    let rets = pp_args(&func.rets);
     let modes = pp_modes(&func.modes);
     args.append(" ->")
         .append(RcDoc::space())
@@ -94,13 +96,15 @@ fn pp_method(func: &FuncType) -> RcDoc<'_> {
         .nest(INDENT_SPACE)
 }
 
-fn pp_args(args: &[IDLType]) -> RcDoc<'_> {
-    let doc = concat(args.iter().map(pp_ty), ",");
-    enclose("(", doc, ")")
-}
-
-fn pp_rets(rets: &[IDLType]) -> RcDoc<'_> {
-    pp_args(rets)
+fn pp_args(args: &[IDLArgType]) -> RcDoc<'_> {
+    let args = args.iter().map(|arg| {
+        if let Some(name) = &arg.name {
+            pp_text(name).append(kwd(" :")).append(pp_ty(&arg.typ))
+        } else {
+            pp_ty(&arg.typ)
+        }
+    });
+    sep_enclose(args, ",", "(", ")")
 }
 
 fn pp_service(methods: &[Binding]) -> RcDoc<'_> {
@@ -119,11 +123,10 @@ fn pp_service_methods(methods: &[Binding]) -> RcDoc<'_> {
             .append(kwd(" :"))
             .append(func_doc)
     });
-    let doc = concat(methods, ";");
-    enclose_space("{", doc, "}")
+    sep_enclose_space(methods, ";", "{", "}")
 }
 
-fn pp_class<'a>(args: &'a [IDLType], t: &'a IDLType) -> RcDoc<'a> {
+fn pp_class<'a>(args: &'a [IDLArgType], t: &'a IDLType) -> RcDoc<'a> {
     let doc = pp_args(args).append(" ->").append(RcDoc::space());
     match t {
         IDLType::ServT(ref serv) => doc.append(pp_service_methods(serv)),
diff --git a/rust/candid_parser/src/test.rs b/rust/candid_parser/src/test.rs
index 10735e941..a25ea91b7 100644
--- a/rust/candid_parser/src/test.rs
+++ b/rust/candid_parser/src/test.rs
@@ -1,5 +1,5 @@
 use super::typing::check_prog;
-use crate::syntax::{Dec, IDLProg, IDLType};
+use crate::syntax::{Dec, IDLArgType, IDLProg};
 use crate::{Error, Result};
 use candid::types::value::IDLArgs;
 use candid::types::{Type, TypeEnv};
@@ -7,7 +7,7 @@ use candid::DecoderConfig;
 
 const DECODING_COST: usize = 20_000_000;
 
-type TupType = Vec<IDLType>;
+type TupType = Vec<IDLArgType>;
 
 pub struct Test {
     pub defs: Vec<Dec>,
@@ -158,7 +158,7 @@ pub fn check(test: Test) -> Result<()> {
         print!("Checking {} {}...", i + 1, assert.desc());
         let mut types = Vec::new();
         for ty in assert.typ.iter() {
-            types.push(super::typing::ast_to_type(&env, ty)?);
+            types.push(super::typing::ast_to_type(&env, &ty.typ)?);
         }
         let input = assert.left.parse(&env, &types);
         let pass = if let Some(assert_right) = &assert.right {
diff --git a/rust/candid_parser/src/typing.rs b/rust/candid_parser/src/typing.rs
index 5179a66fc..6d0e7336a 100644
--- a/rust/candid_parser/src/typing.rs
+++ b/rust/candid_parser/src/typing.rs
@@ -1,12 +1,13 @@
 use crate::{
     pretty_parse,
     syntax::{
-        Binding, Dec, IDLActorType, IDLInitArgs, IDLMergedProg, IDLProg, IDLType, PrimType,
-        TypeField,
+        Binding, Dec, IDLActorType, IDLArgType, IDLInitArgs, IDLMergedProg, IDLProg, IDLType,
+        PrimType, TypeField,
     },
     Error, Result,
 };
-use candid::types::{Field, Function, Type, TypeEnv, TypeInner};
+use candid::types::internal::TypeKey;
+use candid::types::{ArgType, Field, Function, Type, TypeEnv, TypeInner};
 use std::collections::{BTreeMap, BTreeSet};
 use std::path::{Path, PathBuf};
 
@@ -51,8 +52,9 @@ pub fn check_type(env: &Env, t: &IDLType) -> Result<Type> {
     match t {
         IDLType::PrimT(prim) => Ok(check_prim(prim)),
         IDLType::VarT(id) => {
-            env.te.find_type(id)?;
-            Ok(TypeInner::Var(id.to_string()).into())
+            let key = id.as_str().into();
+            env.te.find_type(&key)?;
+            Ok(TypeInner::Var(key).into())
         }
         IDLType::OptT(t) => {
             let t = check_type(env, t)?;
@@ -74,11 +76,11 @@ pub fn check_type(env: &Env, t: &IDLType) -> Result<Type> {
         IDLType::FuncT(func) => {
             let mut t1 = Vec::new();
             for arg in func.args.iter() {
-                t1.push(check_type(env, arg)?);
+                t1.push(check_arg(env, arg)?);
             }
             let mut t2 = Vec::new();
             for t in func.rets.iter() {
-                t2.push(check_type(env, t)?);
+                t2.push(check_arg(env, t)?);
             }
             if func.modes.len() > 1 {
                 return Err(Error::msg("cannot have more than one mode"));
@@ -104,6 +106,13 @@ pub fn check_type(env: &Env, t: &IDLType) -> Result<Type> {
     }
 }
 
+fn check_arg(env: &Env, arg: &IDLArgType) -> Result<ArgType> {
+    Ok(ArgType {
+        name: arg.name.clone(),
+        typ: check_type(env, &arg.typ)?,
+    })
+}
+
 fn check_fields(env: &Env, fs: &[TypeField]) -> Result<Vec<Field>> {
     // field label duplication is checked in the parser
     let mut res = Vec::new();
@@ -139,7 +148,7 @@ fn check_defs(env: &mut Env, decs: &[Dec]) -> Result<()> {
         match dec {
             Dec::TypD(Binding { id, typ, docs: _ }) => {
                 let t = check_type(env, typ)?;
-                env.te.0.insert(id.to_string(), t);
+                env.te.0.insert(id.clone().into(), t);
             }
             Dec::ImportType(_) | Dec::ImportServ(_) => (),
         }
@@ -151,7 +160,7 @@ fn check_cycle(env: &TypeEnv) -> Result<()> {
     fn has_cycle<'a>(seen: &mut BTreeSet<&'a str>, env: &'a TypeEnv, t: &'a Type) -> Result<bool> {
         match t.as_ref() {
             TypeInner::Var(id) => {
-                if seen.insert(id) {
+                if seen.insert(id.as_str()) {
                     let ty = env.find_type(id)?;
                     has_cycle(seen, env, ty)
                 } else {
@@ -170,17 +179,17 @@ fn check_cycle(env: &TypeEnv) -> Result<()> {
     Ok(())
 }
 
-fn validate_func(env: &TypeEnv, seen: &mut BTreeMap<String, bool>, func: &Function) -> Result<()> {
+fn validate_func(env: &TypeEnv, seen: &mut BTreeMap<TypeKey, bool>, func: &Function) -> Result<()> {
     for arg in func.args.iter() {
-        validate_type(env, seen, arg)?;
+        validate_type(env, seen, &arg.typ)?;
     }
     for ret in func.rets.iter() {
-        validate_type(env, seen, ret)?;
+        validate_type(env, seen, &ret.typ)?;
     }
     Ok(())
 }
 
-fn validate_type(env: &TypeEnv, seen: &mut BTreeMap<String, bool>, t: &Type) -> Result<()> {
+fn validate_type(env: &TypeEnv, seen: &mut BTreeMap<TypeKey, bool>, t: &Type) -> Result<()> {
     match t.as_ref() {
         TypeInner::Null
         | TypeInner::Bool
@@ -229,7 +238,7 @@ fn validate_type(env: &TypeEnv, seen: &mut BTreeMap<String, bool>, t: &Type) ->
         }
         TypeInner::Class(args, ty) => {
             for arg in args.iter() {
-                validate_type(env, seen, arg)?;
+                validate_type(env, seen, &arg.typ)?;
             }
             validate_type(env, seen, ty)
         }
@@ -247,7 +256,10 @@ fn validate_decs(env: &TypeEnv) -> Result<()> {
 fn check_decs(env: &mut Env, decs: &[Dec]) -> Result<()> {
     for dec in decs.iter() {
         if let Dec::TypD(Binding { id, .. }) = dec {
-            let duplicate = env.te.0.insert(id.to_string(), TypeInner::Unknown.into());
+            let duplicate = env
+                .te
+                .0
+                .insert(id.as_str().into(), TypeInner::Unknown.into());
             if duplicate.is_some() {
                 return Err(Error::msg(format!("duplicate binding for {id}")));
             }
@@ -267,7 +279,7 @@ fn check_actor(env: &Env, actor: &Option<IDLActorType>) -> Result<Option<Type>>
         Some(IDLType::ClassT(ts, t)) => {
             let mut args = Vec::new();
             for arg in ts.iter() {
-                args.push(check_type(env, arg)?);
+                args.push(check_arg(env, arg)?);
             }
             let serv = check_type(env, t)?;
             env.te.as_service(&serv)?;
@@ -336,13 +348,13 @@ pub fn check_init_args(
     te: &mut TypeEnv,
     main_env: &TypeEnv,
     prog: &IDLInitArgs,
-) -> Result<Vec<Type>> {
+) -> Result<Vec<ArgType>> {
     let mut env = Env { te, pre: false };
     check_decs(&mut env, &prog.decs)?;
     env.te.merge(main_env)?;
     let mut args = Vec::new();
     for arg in prog.args.iter() {
-        args.push(check_type(&env, arg)?);
+        args.push(check_arg(&env, arg)?);
     }
     Ok(args)
 }
diff --git a/rust/candid_parser/src/utils.rs b/rust/candid_parser/src/utils.rs
index 03b0d333e..b9aa58c5e 100644
--- a/rust/candid_parser/src/utils.rs
+++ b/rust/candid_parser/src/utils.rs
@@ -1,4 +1,5 @@
 use crate::{check_prog, pretty_check_file, pretty_parse, Error, Result};
+use candid::types::internal::TypeKey;
 use candid::{
     types::{Type, TypeInner},
     TypeEnv,
@@ -78,7 +79,10 @@ pub fn instantiate_candid(candid: CandidSource) -> Result<(Vec<Type>, (TypeEnv,
     let serv = serv.ok_or_else(|| Error::msg("the Candid interface has no main service type"))?;
     let serv = env.trace_type(&serv)?;
     Ok(match serv.as_ref() {
-        TypeInner::Class(args, ty) => (args.clone(), (env, ty.clone())),
+        TypeInner::Class(args, ty) => (
+            args.iter().map(|arg| arg.typ.clone()).collect::<Vec<_>>(),
+            (env, ty.clone()),
+        ),
         TypeInner::Service(_) => (vec![], (env, serv)),
         _ => unreachable!(),
     })
@@ -94,8 +98,8 @@ pub fn get_metadata(env: &TypeEnv, serv: &Option<Type>) -> Option<String> {
     let def_list = crate::bindings::analysis::chase_actor(env, &serv).ok()?;
     let mut filtered = TypeEnv::new();
     for d in def_list {
-        if let Some(t) = env.0.get(d) {
-            filtered.0.insert(d.to_string(), t.clone());
+        if let Some(t) = env.0.get(&TypeKey::from(d)) {
+            filtered.0.insert(d.to_string().into(), t.clone());
         }
     }
     Some(candid::pretty::candid::compile(&filtered, &Some(serv)))
@@ -134,6 +138,6 @@ pub fn check_rust_type<T: candid::CandidType>(candid_args: &str) -> Result<()> {
     let ty = rust_env.add::<T>();
     let ty = env.merge_type(rust_env.env, ty);
     let mut gamma = std::collections::HashSet::new();
-    equal(&mut gamma, &env, &args[0], &ty)?;
+    equal(&mut gamma, &env, &args[0].typ, &ty)?;
     Ok(())
 }
diff --git a/rust/candid_parser/tests/assets/collision_arguments.did b/rust/candid_parser/tests/assets/collision_arguments.did
new file mode 100644
index 000000000..c7f3117e0
--- /dev/null
+++ b/rust/candid_parser/tests/assets/collision_arguments.did
@@ -0,0 +1,4 @@
+type f = func (a : nat, b : bool, a : text) -> ();
+service : {
+    f : f;
+};
diff --git a/rust/candid_parser/tests/assets/collision_arguments2.did b/rust/candid_parser/tests/assets/collision_arguments2.did
new file mode 100644
index 000000000..0a4773fe6
--- /dev/null
+++ b/rust/candid_parser/tests/assets/collision_arguments2.did
@@ -0,0 +1,3 @@
+service : (b : nat, bool, b : text) -> {
+    f : (text, text) -> ();
+};
diff --git a/rust/candid_parser/tests/assets/ok/actor.d.ts b/rust/candid_parser/tests/assets/ok/actor.d.ts
index ce5b7ef2b..80ef1a413 100644
--- a/rust/candid_parser/tests/assets/ok/actor.d.ts
+++ b/rust/candid_parser/tests/assets/ok/actor.d.ts
@@ -13,5 +13,7 @@ export interface _SERVICE {
   'h2' : h,
   'o' : ActorMethod<[o], o>,
 }
+export declare const idlService: IDL.ServiceClass;
+export declare const idlInitArgs: IDL.Type[];
 export declare const idlFactory: IDL.InterfaceFactory;
 export declare const init: (args: { IDL: typeof IDL }) => IDL.Type[];
diff --git a/rust/candid_parser/tests/assets/ok/actor.js b/rust/candid_parser/tests/assets/ok/actor.js
index 9d59adae4..b6682ed29 100644
--- a/rust/candid_parser/tests/assets/ok/actor.js
+++ b/rust/candid_parser/tests/assets/ok/actor.js
@@ -1,9 +1,28 @@
+import { IDL } from '@dfinity/candid';
+
+export const o = IDL.Rec();
+export const f = IDL.Func([IDL.Int8], [IDL.Int8], []);
+export const h = IDL.Func([f], [f], []);
+export const g = f;
+o.fill(IDL.Opt(o));
+
+export const idlService = IDL.Service({
+  'f' : IDL.Func([IDL.Nat], [h], []),
+  'g' : f,
+  'h' : g,
+  'h2' : h,
+  'o' : IDL.Func([o], [o], []),
+});
+
+export const idlInitArgs = [];
+
 export const idlFactory = ({ IDL }) => {
   const o = IDL.Rec();
   const f = IDL.Func([IDL.Int8], [IDL.Int8], []);
   const h = IDL.Func([f], [f], []);
   const g = f;
   o.fill(IDL.Opt(o));
+  
   return IDL.Service({
     'f' : IDL.Func([IDL.Nat], [h], []),
     'g' : f,
@@ -12,4 +31,5 @@ export const idlFactory = ({ IDL }) => {
     'o' : IDL.Func([o], [o], []),
   });
 };
+
 export const init = ({ IDL }) => { return []; };
diff --git a/rust/candid_parser/tests/assets/ok/actor.mo b/rust/candid_parser/tests/assets/ok/actor.mo
index 98531f3fc..46d5a4332 100644
--- a/rust/candid_parser/tests/assets/ok/actor.mo
+++ b/rust/candid_parser/tests/assets/ok/actor.mo
@@ -2,10 +2,10 @@
 // Please use `import service "ic:canister_id"` instead to call canisters on the IC if possible.
 
 module {
-  public type f = shared Int8 -> async Int8;
   public type g = f;
-  public type h = shared f -> async f;
   public type o = ?o;
+  public type f = shared Int8 -> async Int8;
+  public type h = shared f -> async f;
   public type Self = actor {
     f : shared Nat -> async h;
     g : f;
diff --git a/rust/candid_parser/tests/assets/ok/class.d.ts b/rust/candid_parser/tests/assets/ok/class.d.ts
index 9a35748bc..7a68e4073 100644
--- a/rust/candid_parser/tests/assets/ok/class.d.ts
+++ b/rust/candid_parser/tests/assets/ok/class.d.ts
@@ -14,5 +14,7 @@ export interface _SERVICE {
   'get' : ActorMethod<[], List>,
   'set' : ActorMethod<[List], List>,
 }
+export declare const idlService: IDL.ServiceClass;
+export declare const idlInitArgs: IDL.Type[];
 export declare const idlFactory: IDL.InterfaceFactory;
 export declare const init: (args: { IDL: typeof IDL }) => IDL.Type[];
diff --git a/rust/candid_parser/tests/assets/ok/class.did b/rust/candid_parser/tests/assets/ok/class.did
index 494dcc3bf..a33497f3e 100644
--- a/rust/candid_parser/tests/assets/ok/class.did
+++ b/rust/candid_parser/tests/assets/ok/class.did
@@ -1,7 +1,7 @@
 type Profile = record { age : nat8; name : text };
 type List = opt record { int; List };
 // Doc comment for class service
-service : (int, List, Profile) -> {
+service : (int, l : List, Profile) -> {
   // Doc comment for get method in class service
   get : () -> (List);
   set : (List) -> (List);
diff --git a/rust/candid_parser/tests/assets/ok/class.js b/rust/candid_parser/tests/assets/ok/class.js
index 5f052ee01..8ab176452 100644
--- a/rust/candid_parser/tests/assets/ok/class.js
+++ b/rust/candid_parser/tests/assets/ok/class.js
@@ -1,15 +1,31 @@
+import { IDL } from '@dfinity/candid';
+
+export const List = IDL.Rec();
+List.fill(IDL.Opt(IDL.Tuple(IDL.Int, List)));
+export const Profile = IDL.Record({ 'age' : IDL.Nat8, 'name' : IDL.Text });
+
+export const idlService = IDL.Service({
+  'get' : IDL.Func([], [List], []),
+  'set' : IDL.Func([List], [List], []),
+});
+
+export const idlInitArgs = [IDL.Int, List, Profile];
+
 export const idlFactory = ({ IDL }) => {
   const List = IDL.Rec();
   List.fill(IDL.Opt(IDL.Tuple(IDL.Int, List)));
   const Profile = IDL.Record({ 'age' : IDL.Nat8, 'name' : IDL.Text });
+  
   return IDL.Service({
     'get' : IDL.Func([], [List], []),
     'set' : IDL.Func([List], [List], []),
   });
 };
+
 export const init = ({ IDL }) => {
   const List = IDL.Rec();
   List.fill(IDL.Opt(IDL.Tuple(IDL.Int, List)));
   const Profile = IDL.Record({ 'age' : IDL.Nat8, 'name' : IDL.Text });
+  
   return [IDL.Int, List, Profile];
 };
diff --git a/rust/candid_parser/tests/assets/ok/class.mo b/rust/candid_parser/tests/assets/ok/class.mo
index 8b9458c7f..454a3f2f8 100644
--- a/rust/candid_parser/tests/assets/ok/class.mo
+++ b/rust/candid_parser/tests/assets/ok/class.mo
@@ -5,7 +5,7 @@ module {
   public type List = ?(Int, List);
   public type Profile = { age : Nat8; name : Text };
   /// Doc comment for class service
-  public type Self = (Int, List, Profile) -> async actor {
+  public type Self = (Int, l : List, Profile) -> async actor {
     /// Doc comment for get method in class service
     get : shared () -> async List;
     set : shared List -> async List;
diff --git a/rust/candid_parser/tests/assets/ok/class.rs b/rust/candid_parser/tests/assets/ok/class.rs
index c48738646..f7f94db2d 100644
--- a/rust/candid_parser/tests/assets/ok/class.rs
+++ b/rust/candid_parser/tests/assets/ok/class.rs
@@ -4,12 +4,12 @@
 use candid::{self, CandidType, Deserialize, Principal};
 
 #[derive(CandidType, Deserialize)]
-pub struct List(pub Option<(candid::Int,Box<List>,)>);
+pub struct List(pub Option<(candid::Int, Box<List>)>);
 #[derive(CandidType, Deserialize)]
 pub struct Profile { pub age: u8, pub name: String }
 
 #[ic_cdk::init]
-fn init(arg0: candid::Int, arg1: List, arg2: Profile) {
+fn init(arg0: candid::Int, l: List, arg2: Profile) {
   unimplemented!()
 }
 /// Doc comment for get method in class service
diff --git a/rust/candid_parser/tests/assets/ok/collision_arguments.fail b/rust/candid_parser/tests/assets/ok/collision_arguments.fail
new file mode 100644
index 000000000..9aa36e9cc
--- /dev/null
+++ b/rust/candid_parser/tests/assets/ok/collision_arguments.fail
@@ -0,0 +1 @@
+Candid parser error: label 'a' hash collision with 'a'
diff --git a/rust/candid_parser/tests/assets/ok/collision_arguments2.fail b/rust/candid_parser/tests/assets/ok/collision_arguments2.fail
new file mode 100644
index 000000000..0c2043a40
--- /dev/null
+++ b/rust/candid_parser/tests/assets/ok/collision_arguments2.fail
@@ -0,0 +1 @@
+Candid parser error: label 'b' hash collision with 'b'
diff --git a/rust/candid_parser/tests/assets/ok/comment.js b/rust/candid_parser/tests/assets/ok/comment.js
index 1f63d4782..6a3800d13 100644
--- a/rust/candid_parser/tests/assets/ok/comment.js
+++ b/rust/candid_parser/tests/assets/ok/comment.js
@@ -1,2 +1,5 @@
-const id = IDL.Nat8;
+import { IDL } from '@dfinity/candid';
+
+export const id = IDL.Nat8;
+
 
diff --git a/rust/candid_parser/tests/assets/ok/cyclic.d.ts b/rust/candid_parser/tests/assets/ok/cyclic.d.ts
index 908e3e263..3c9470181 100644
--- a/rust/candid_parser/tests/assets/ok/cyclic.d.ts
+++ b/rust/candid_parser/tests/assets/ok/cyclic.d.ts
@@ -9,5 +9,7 @@ export type X = Y;
 export type Y = Z;
 export type Z = A;
 export interface _SERVICE { 'f' : ActorMethod<[A, B, C, X, Y, Z], undefined> }
+export declare const idlService: IDL.ServiceClass;
+export declare const idlInitArgs: IDL.Type[];
 export declare const idlFactory: IDL.InterfaceFactory;
 export declare const init: (args: { IDL: typeof IDL }) => IDL.Type[];
diff --git a/rust/candid_parser/tests/assets/ok/cyclic.js b/rust/candid_parser/tests/assets/ok/cyclic.js
index 528eaa6f3..8a04059a4 100644
--- a/rust/candid_parser/tests/assets/ok/cyclic.js
+++ b/rust/candid_parser/tests/assets/ok/cyclic.js
@@ -1,3 +1,19 @@
+import { IDL } from '@dfinity/candid';
+
+export const A = IDL.Rec();
+export const C = A;
+export const B = IDL.Opt(C);
+A.fill(IDL.Opt(B));
+export const Z = A;
+export const Y = Z;
+export const X = Y;
+
+export const idlService = IDL.Service({
+  'f' : IDL.Func([A, B, C, X, Y, Z], [], []),
+});
+
+export const idlInitArgs = [];
+
 export const idlFactory = ({ IDL }) => {
   const A = IDL.Rec();
   const C = A;
@@ -6,6 +22,8 @@ export const idlFactory = ({ IDL }) => {
   const Z = A;
   const Y = Z;
   const X = Y;
+  
   return IDL.Service({ 'f' : IDL.Func([A, B, C, X, Y, Z], [], []) });
 };
+
 export const init = ({ IDL }) => { return []; };
diff --git a/rust/candid_parser/tests/assets/ok/cyclic.mo b/rust/candid_parser/tests/assets/ok/cyclic.mo
index 4ca4a600a..7bae9418e 100644
--- a/rust/candid_parser/tests/assets/ok/cyclic.mo
+++ b/rust/candid_parser/tests/assets/ok/cyclic.mo
@@ -3,10 +3,10 @@
 
 module {
   public type A = ?B;
-  public type B = ?C;
-  public type C = A;
+  public type Z = A;
   public type X = Y;
+  public type C = A;
   public type Y = Z;
-  public type Z = A;
+  public type B = ?C;
   public type Self = actor { f : shared (A, B, C, X, Y, Z) -> async () }
 }
diff --git a/rust/candid_parser/tests/assets/ok/empty.d.ts b/rust/candid_parser/tests/assets/ok/empty.d.ts
index 315885bfb..ab794a341 100644
--- a/rust/candid_parser/tests/assets/ok/empty.d.ts
+++ b/rust/candid_parser/tests/assets/ok/empty.d.ts
@@ -8,5 +8,7 @@ export interface _SERVICE {
   'g' : ActorMethod<[T], { 'a' : T }>,
   'h' : ActorMethod<[[T, never]], { 'a' : T } | { 'b' : {} }>,
 }
+export declare const idlService: IDL.ServiceClass;
+export declare const idlInitArgs: IDL.Type[];
 export declare const idlFactory: IDL.InterfaceFactory;
 export declare const init: (args: { IDL: typeof IDL }) => IDL.Type[];
diff --git a/rust/candid_parser/tests/assets/ok/empty.js b/rust/candid_parser/tests/assets/ok/empty.js
index 74b91c7cc..a4d036997 100644
--- a/rust/candid_parser/tests/assets/ok/empty.js
+++ b/rust/candid_parser/tests/assets/ok/empty.js
@@ -1,6 +1,24 @@
+import { IDL } from '@dfinity/candid';
+
+export const T = IDL.Rec();
+T.fill(IDL.Tuple(T));
+
+export const idlService = IDL.Service({
+  'f' : IDL.Func([IDL.Record({})], [IDL.Variant({})], []),
+  'g' : IDL.Func([T], [IDL.Variant({ 'a' : T })], []),
+  'h' : IDL.Func(
+      [IDL.Tuple(T, IDL.Empty)],
+      [IDL.Variant({ 'a' : T, 'b' : IDL.Record({}) })],
+      [],
+    ),
+});
+
+export const idlInitArgs = [];
+
 export const idlFactory = ({ IDL }) => {
   const T = IDL.Rec();
   T.fill(IDL.Tuple(T));
+  
   return IDL.Service({
     'f' : IDL.Func([IDL.Record({})], [IDL.Variant({})], []),
     'g' : IDL.Func([T], [IDL.Variant({ 'a' : T })], []),
@@ -11,4 +29,5 @@ export const idlFactory = ({ IDL }) => {
       ),
   });
 };
+
 export const init = ({ IDL }) => { return []; };
diff --git a/rust/candid_parser/tests/assets/ok/empty.rs b/rust/candid_parser/tests/assets/ok/empty.rs
index 899477cc8..81d1ed30c 100644
--- a/rust/candid_parser/tests/assets/ok/empty.rs
+++ b/rust/candid_parser/tests/assets/ok/empty.rs
@@ -9,7 +9,7 @@ pub struct FArg {}
 #[derive(CandidType, Deserialize)]
 pub enum FRet {}
 #[derive(CandidType, Deserialize)]
-pub struct T (pub Box<T>,);
+pub struct T (pub Box<T>);
 #[derive(CandidType, Deserialize)]
 pub enum GRet { #[serde(rename="a")] A(Box<T>) }
 #[derive(CandidType, Deserialize)]
@@ -23,7 +23,7 @@ impl Service {
   pub async fn g(&self, arg0: &T) -> Result<(GRet,)> {
     ic_cdk::call(self.0, "g", (arg0,)).await
   }
-  pub async fn h(&self, arg0: &(T,candid::Empty,)) -> Result<(HRet,)> {
+  pub async fn h(&self, arg0: &(T, candid::Empty)) -> Result<(HRet,)> {
     ic_cdk::call(self.0, "h", (arg0,)).await
   }
 }
diff --git a/rust/candid_parser/tests/assets/ok/escape.d.ts b/rust/candid_parser/tests/assets/ok/escape.d.ts
index 0908479b7..08ff97894 100644
--- a/rust/candid_parser/tests/assets/ok/escape.d.ts
+++ b/rust/candid_parser/tests/assets/ok/escape.d.ts
@@ -9,5 +9,7 @@ export interface t {
   '\\\n\'\"' : bigint,
 }
 export interface _SERVICE { '\n\'\"\'\'\"\"\r\t' : ActorMethod<[t], undefined> }
+export declare const idlService: IDL.ServiceClass;
+export declare const idlInitArgs: IDL.Type[];
 export declare const idlFactory: IDL.InterfaceFactory;
 export declare const init: (args: { IDL: typeof IDL }) => IDL.Type[];
diff --git a/rust/candid_parser/tests/assets/ok/escape.js b/rust/candid_parser/tests/assets/ok/escape.js
index b46d9cebf..68e3b466d 100644
--- a/rust/candid_parser/tests/assets/ok/escape.js
+++ b/rust/candid_parser/tests/assets/ok/escape.js
@@ -1,3 +1,18 @@
+import { IDL } from '@dfinity/candid';
+
+export const t = IDL.Record({
+  '\"' : IDL.Nat,
+  '\'' : IDL.Nat,
+  '\"\'' : IDL.Nat,
+  '\\\n\'\"' : IDL.Nat,
+});
+
+export const idlService = IDL.Service({
+  '\n\'\"\'\'\"\"\r\t' : IDL.Func([t], [], []),
+});
+
+export const idlInitArgs = [];
+
 export const idlFactory = ({ IDL }) => {
   const t = IDL.Record({
     '\"' : IDL.Nat,
@@ -5,6 +20,8 @@ export const idlFactory = ({ IDL }) => {
     '\"\'' : IDL.Nat,
     '\\\n\'\"' : IDL.Nat,
   });
+  
   return IDL.Service({ '\n\'\"\'\'\"\"\r\t' : IDL.Func([t], [], []) });
 };
+
 export const init = ({ IDL }) => { return []; };
diff --git a/rust/candid_parser/tests/assets/ok/example.d.ts b/rust/candid_parser/tests/assets/ok/example.d.ts
index de431ffb9..c8fdceff7 100644
--- a/rust/candid_parser/tests/assets/ok/example.d.ts
+++ b/rust/candid_parser/tests/assets/ok/example.d.ts
@@ -187,5 +187,7 @@ export interface _SERVICE {
    */
   'bbbbb' : ActorMethod<[b], undefined>,
 }
+export declare const idlService: IDL.ServiceClass;
+export declare const idlInitArgs: IDL.Type[];
 export declare const idlFactory: IDL.InterfaceFactory;
 export declare const init: (args: { IDL: typeof IDL }) => IDL.Type[];
diff --git a/rust/candid_parser/tests/assets/ok/example.did b/rust/candid_parser/tests/assets/ok/example.did
index 3dd731662..48980d55d 100644
--- a/rust/candid_parser/tests/assets/ok/example.did
+++ b/rust/candid_parser/tests/assets/ok/example.did
@@ -10,7 +10,7 @@ type List = opt record {
 type f = func (List, func (int32) -> (int64)) -> (opt List, res);
 // Doc comment for broker service
 type broker = service {
-  find : (text) -> (service { current : () -> (nat32); up : () -> () });
+  find : (name : text) -> (service { current : () -> (nat32); up : () -> () });
 };
 // Doc comment for nested type
 type nested = record {
@@ -77,14 +77,14 @@ type tree = variant {
 };
 // Doc comment for service id
 type s = service { f : t; g : (list) -> (B, tree, stream) };
-type t = func (s) -> ();
+type t = func (server : s) -> ();
 type stream = opt record { head : nat; next : func () -> (stream) query };
 type b = record { int; nat };
 type a = variant { a; b : b };
 // Doc comment for service
 service : {
   // Doc comment for f1 method of service
-  f1 : (list, blob, opt bool) -> () oneway;
+  f1 : (list, test : blob, opt bool) -> () oneway;
   g1 : (my_type, List, opt List, nested) -> (int, broker, nested_res) query;
   h : (vec opt text, variant { A : nat; B : opt text }, opt List) -> (
       record {
diff --git a/rust/candid_parser/tests/assets/ok/example.js b/rust/candid_parser/tests/assets/ok/example.js
index fe10e4cef..5a609879c 100644
--- a/rust/candid_parser/tests/assets/ok/example.js
+++ b/rust/candid_parser/tests/assets/ok/example.js
@@ -1,3 +1,128 @@
+import { IDL } from '@dfinity/candid';
+
+export const B = IDL.Rec();
+export const List = IDL.Rec();
+export const list = IDL.Rec();
+export const stream = IDL.Rec();
+export const t = IDL.Rec();
+export const tree = IDL.Rec();
+export const node = IDL.Record({ 'head' : IDL.Nat, 'tail' : list });
+list.fill(IDL.Opt(node));
+export const my_type = IDL.Principal;
+List.fill(IDL.Opt(IDL.Record({ 'head' : IDL.Int, 'tail' : List })));
+export const nested = IDL.Record({
+  _0_ : IDL.Nat,
+  _1_ : IDL.Nat,
+  _2_ : IDL.Tuple(IDL.Nat, IDL.Int),
+  _3_ : IDL.Record({ _0_ : IDL.Nat, _42_ : IDL.Nat, _43_ : IDL.Nat8 }),
+  _40_ : IDL.Nat,
+  _41_ : IDL.Variant({
+    _42_ : IDL.Null,
+    'A' : IDL.Null,
+    'B' : IDL.Null,
+    'C' : IDL.Null,
+  }),
+  _42_ : IDL.Nat,
+});
+export const broker = IDL.Service({
+  'find' : IDL.Func(
+      [IDL.Text],
+      [
+        IDL.Service({
+          'current' : IDL.Func([], [IDL.Nat32], []),
+          'up' : IDL.Func([], [], []),
+        }),
+      ],
+      [],
+    ),
+});
+export const nested_res = IDL.Variant({
+  'Ok' : IDL.Variant({ 'Ok' : IDL.Null, 'Err' : IDL.Null }),
+  'Err' : IDL.Variant({
+    'Ok' : IDL.Record({ 'content' : IDL.Text }),
+    'Err' : IDL.Tuple(IDL.Int),
+  }),
+});
+export const res = IDL.Variant({
+  'Ok' : IDL.Tuple(IDL.Int, IDL.Nat),
+  'Err' : IDL.Record({ 'error' : IDL.Text }),
+});
+export const f = IDL.Func(
+    [List, IDL.Func([IDL.Int32], [IDL.Int64], [])],
+    [IDL.Opt(List), res],
+    [],
+  );
+export const b = IDL.Tuple(IDL.Int, IDL.Nat);
+export const a = IDL.Variant({ 'a' : IDL.Null, 'b' : b });
+export const nested_records = IDL.Record({
+  'nested' : IDL.Opt(IDL.Record({ 'nested_field' : IDL.Text })),
+});
+export const my_variant = IDL.Variant({
+  'a' : IDL.Record({ 'b' : IDL.Text }),
+  'c' : IDL.Opt(
+    IDL.Record({ 'd' : IDL.Text, 'e' : IDL.Vec(IDL.Record({ 'f' : IDL.Nat })) })
+  ),
+});
+export const A = B;
+B.fill(IDL.Opt(A));
+tree.fill(
+  IDL.Variant({
+    'branch' : IDL.Record({ 'val' : IDL.Int, 'left' : tree, 'right' : tree }),
+    'leaf' : IDL.Int,
+  })
+);
+stream.fill(
+  IDL.Opt(
+    IDL.Record({ 'head' : IDL.Nat, 'next' : IDL.Func([], [stream], ['query']) })
+  )
+);
+export const s = IDL.Service({
+  'f' : t,
+  'g' : IDL.Func([list], [B, tree, stream], []),
+});
+t.fill(IDL.Func([s], [], []));
+
+export const idlService = IDL.Service({
+  'f1' : IDL.Func([list, IDL.Vec(IDL.Nat8), IDL.Opt(IDL.Bool)], [], ['oneway']),
+  'g1' : IDL.Func(
+      [my_type, List, IDL.Opt(List), nested],
+      [IDL.Int, broker, nested_res],
+      ['query'],
+    ),
+  'h' : IDL.Func(
+      [
+        IDL.Vec(IDL.Opt(IDL.Text)),
+        IDL.Variant({ 'A' : IDL.Nat, 'B' : IDL.Opt(IDL.Text) }),
+        IDL.Opt(List),
+      ],
+      [IDL.Record({ _42_ : IDL.Record({}), 'id' : IDL.Nat })],
+      [],
+    ),
+  'i' : f,
+  'x' : IDL.Func(
+      [a, b],
+      [
+        IDL.Opt(a),
+        IDL.Opt(b),
+        IDL.Variant({
+          'Ok' : IDL.Record({ 'result' : IDL.Text }),
+          'Err' : IDL.Variant({ 'a' : IDL.Null, 'b' : IDL.Null }),
+        }),
+      ],
+      ['composite_query'],
+    ),
+  'y' : IDL.Func(
+      [nested_records],
+      [IDL.Tuple(nested_records, my_variant)],
+      ['query'],
+    ),
+  'f' : t,
+  'g' : IDL.Func([list], [B, tree, stream], []),
+  'bbbbb' : IDL.Func([b], [], []),
+});
+
+export const idlInitArgs = [];
+
 export const idlFactory = ({ IDL }) => {
   const B = IDL.Rec();
   const List = IDL.Rec();
@@ -86,6 +211,7 @@ export const idlFactory = ({ IDL }) => {
     'g' : IDL.Func([list], [B, tree, stream], []),
   });
   t.fill(IDL.Func([s], [], []));
+  
   return IDL.Service({
     'f1' : IDL.Func(
         [list, IDL.Vec(IDL.Nat8), IDL.Opt(IDL.Bool)],
@@ -129,4 +255,5 @@ export const idlFactory = ({ IDL }) => {
     'bbbbb' : IDL.Func([b], [], []),
   });
 };
+
 export const init = ({ IDL }) => { return []; };
diff --git a/rust/candid_parser/tests/assets/ok/example.mo b/rust/candid_parser/tests/assets/ok/example.mo
index 8dd8d9bf9..13381c772 100644
--- a/rust/candid_parser/tests/assets/ok/example.mo
+++ b/rust/candid_parser/tests/assets/ok/example.mo
@@ -2,31 +2,6 @@
 // Please use `import service "ic:canister_id"` instead to call canisters on the IC if possible.
 
 module {
-  public type A = B;
-  public type B = ?A;
-  /// Doc comment for List
-  public type List = ?{
-    /// Doc comment for List head
-    head : Int;
-    /// Doc comment for List tail
-    tail : List;
-  };
-  public type a = { #a; #b : b };
-  public type b = (Int, Nat);
-  /// Doc comment for broker service
-  public type broker = actor {
-    find : shared Text -> async actor {
-        current : shared () -> async Nat32;
-        up : shared () -> async ();
-      };
-  };
-  public type f = shared (List, shared Int32 -> async Int64) -> async (
-      ?List,
-      res,
-    );
-  public type list = ?node;
-  /// Doc comment for prim type
-  public type my_type = Principal;
   public type my_variant = {
     /// Doc comment for my_variant field a
     #a : {
@@ -45,6 +20,38 @@ module {
       ];
     };
   };
+  /// Doc comment for service id
+  public type s = actor { f : t; g : shared list -> async (B, tree, stream) };
+  /// Doc comment for List
+  public type List = ?{
+    /// Doc comment for List head
+    head : Int;
+    /// Doc comment for List tail
+    tail : List;
+  };
+  public type list = ?node;
+  public type tree = {
+    #branch : { val : Int; left : tree; right : tree };
+    #leaf : Int;
+  };
+  public type a = { #a; #b : b };
+  /// Doc comment for broker service
+  public type broker = actor {
+    find : shared (name : Text) -> async actor {
+        current : shared () -> async Nat32;
+        up : shared () -> async ();
+      };
+  };
+  public type t = shared (server : s) -> async ();
+  /// Doc comment for prim type
+  public type my_type = Principal;
+  public type f = shared (List, shared Int32 -> async Int64) -> async (
+      ?List,
+      res,
+    );
+  public type b = (Int, Nat);
+  public type stream = ?{ head : Nat; next : shared query () -> async stream };
+  public type A = B;
   /// Doc comment for nested type
   public type nested = {
     _0_  : Nat;
@@ -56,14 +63,6 @@ module {
     _41_  : { #_42_ ; #A; #B; #C };
     _42_  : Nat;
   };
-  /// Doc comment for nested_records
-  public type nested_records = {
-    /// Doc comment for nested_records field nested
-    nested : ?{
-      /// Doc comment for nested_records field nested_field
-      nested_field : Text;
-    };
-  };
   public type nested_res = {
     #Ok : { #Ok; #Err };
     #Err : {
@@ -73,7 +72,15 @@ module {
       #Err : { _0_  : Int };
     };
   };
-  public type node = { head : Nat; tail : list };
+  /// Doc comment for nested_records
+  public type nested_records = {
+    /// Doc comment for nested_records field nested
+    nested : ?{
+      /// Doc comment for nested_records field nested_field
+      nested_field : Text;
+    };
+  };
+  public type B = ?A;
   /// Doc comment for res type
   public type res = {
     /// Doc comment for Ok variant
@@ -85,18 +92,11 @@ module {
       error : Text;
     };
   };
-  /// Doc comment for service id
-  public type s = actor { f : t; g : shared list -> async (B, tree, stream) };
-  public type stream = ?{ head : Nat; next : shared query () -> async stream };
-  public type t = shared s -> async ();
-  public type tree = {
-    #branch : { val : Int; left : tree; right : tree };
-    #leaf : Int;
-  };
+  public type node = { head : Nat; tail : list };
   /// Doc comment for service
   public type Self = actor {
     /// Doc comment for f1 method of service
-    f1 : shared (list, Blob, ?Bool) -> ();
+    f1 : shared (list, test : Blob, ?Bool) -> ();
     g1 : shared query (my_type, List, ?List, nested) -> async (
         Int,
         broker,
diff --git a/rust/candid_parser/tests/assets/ok/example.rs b/rust/candid_parser/tests/assets/ok/example.rs
index 6b800e6cb..c7c105244 100644
--- a/rust/candid_parser/tests/assets/ok/example.rs
+++ b/rust/candid_parser/tests/assets/ok/example.rs
@@ -44,7 +44,7 @@ pub(crate) struct Nested {
   pub(crate) _0_: u128,
   pub(crate) _1_: u128,
   /// Doc comment for nested record
-  pub(crate) _2_: (u128,candid::Int,),
+  pub(crate) _2_: (u128, candid::Int),
   pub(crate) _3_: Nested3,
   pub(crate) _40_: u128,
   pub(crate) _41_: Nested41,
@@ -60,7 +60,7 @@ candid::define_service!(pub(crate) Broker : {
 #[derive(CandidType, Deserialize, Debug)]
 pub(crate) struct NestedResErrOk { pub(crate) content: String }
 pub(crate) type NestedRes = std::result::Result<
-  my::Result<(), ()>, another::Result<NestedResErrOk, (candid::Int,)>
+  my::Result<(), ()>, another::Result<NestedResErrOk, (candid::Int)>
 >;
 #[derive(CandidType, Deserialize, Debug)]
 pub(crate) enum HArg1 { A(u128), B(Option<String>) }
@@ -76,13 +76,13 @@ pub(crate) struct ResErr {
   pub(crate) error: String,
 }
 /// Doc comment for res type
-pub(crate) type Res = std::result::Result<(candid::Int,u128,), ResErr>;
+pub(crate) type Res = std::result::Result<(candid::Int, u128), ResErr>;
 candid::define_function!(pub(crate) F : (MyList, FArg1) -> (
     Option<MyList>,
     Res,
   ));
 #[derive(CandidType, Deserialize, Debug)]
-pub(crate) struct B (pub(crate) candid::Int,pub(crate) u128,);
+pub(crate) struct B (pub(crate) candid::Int, pub(crate) u128);
 #[derive(CandidType, Deserialize, Debug)]
 pub(crate) enum A { #[serde(rename="a")] A, #[serde(rename="b")] B(B) }
 #[derive(CandidType, Deserialize, Debug)]
@@ -151,8 +151,8 @@ candid::define_function!(pub(crate) T : (S) -> ());
 pub struct Service(pub Principal);
 impl Service {
   /// Doc comment for f1 method of service
-  pub async fn f1(&self, arg0: &List, arg1: &serde_bytes::ByteBuf, arg2: &Option<bool>) -> Result<()> {
-    ic_cdk::call(self.0, "f1", (arg0,arg1,arg2,)).await
+  pub async fn f1(&self, arg0: &List, test: &serde_bytes::ByteBuf, arg2: &Option<bool>) -> Result<()> {
+    ic_cdk::call(self.0, "f1", (arg0,test,arg2,)).await
   }
   pub async fn G11(&self, id: &CanisterId, list: &MyList, is_okay: &Option<MyList>, arg3: &Nested) -> Result<(i128,Broker,NestedRes,)> {
     ic_cdk::call(self.0, "g1", (id,list,is_okay,arg3,)).await
@@ -167,11 +167,11 @@ impl Service {
   pub async fn x(&self, arg0: &A, arg1: &B) -> Result<(Option<A>,Option<B>,std::result::Result<XRet2Ok, Error>,)> {
     ic_cdk::call(self.0, "x", (arg0,arg1,)).await
   }
-  pub async fn y(&self, arg0: &NestedRecords) -> Result<((NestedRecords,MyVariant,),)> {
+  pub async fn y(&self, arg0: &NestedRecords) -> Result<((NestedRecords, MyVariant),)> {
     ic_cdk::call(self.0, "y", (arg0,)).await
   }
-  pub async fn f(&self, arg0: &S) -> Result<()> {
-    ic_cdk::call(self.0, "f", (arg0,)).await
+  pub async fn f(&self, server: &S) -> Result<()> {
+    ic_cdk::call(self.0, "f", (server,)).await
   }
   pub async fn g(&self, arg0: &List) -> Result<(B,Tree,Stream,)> {
     ic_cdk::call(self.0, "g", (arg0,)).await
diff --git a/rust/candid_parser/tests/assets/ok/fieldnat.d.ts b/rust/candid_parser/tests/assets/ok/fieldnat.d.ts
index ec5bad50f..bbd788e03 100644
--- a/rust/candid_parser/tests/assets/ok/fieldnat.d.ts
+++ b/rust/candid_parser/tests/assets/ok/fieldnat.d.ts
@@ -13,5 +13,7 @@ export interface _SERVICE {
   'bib' : ActorMethod<[[bigint]], { _0_ : bigint }>,
   'foo' : ActorMethod<[{ _2_ : bigint }], { _2_ : bigint, '_2' : bigint }>,
 }
+export declare const idlService: IDL.ServiceClass;
+export declare const idlInitArgs: IDL.Type[];
 export declare const idlFactory: IDL.InterfaceFactory;
 export declare const init: (args: { IDL: typeof IDL }) => IDL.Type[];
diff --git a/rust/candid_parser/tests/assets/ok/fieldnat.did b/rust/candid_parser/tests/assets/ok/fieldnat.did
index 7855c696a..1f5e2a585 100644
--- a/rust/candid_parser/tests/assets/ok/fieldnat.did
+++ b/rust/candid_parser/tests/assets/ok/fieldnat.did
@@ -1,7 +1,7 @@
 type tuple = record { text; text };
 type non_tuple = record { 1 : text; 2 : text };
 service : {
-  bab : (int, nat) -> ();
+  bab : (two : int, nat) -> ();
   bar : (record { "2" : int }) -> (variant { e20; e30 });
   bas : (record { int; int }) -> (record { text; nat });
   baz : (record { 2 : int; "2" : nat }) -> (record {});
diff --git a/rust/candid_parser/tests/assets/ok/fieldnat.js b/rust/candid_parser/tests/assets/ok/fieldnat.js
index 590e67cdd..f0154adec 100644
--- a/rust/candid_parser/tests/assets/ok/fieldnat.js
+++ b/rust/candid_parser/tests/assets/ok/fieldnat.js
@@ -1,6 +1,40 @@
+import { IDL } from '@dfinity/candid';
+
+export const tuple = IDL.Tuple(IDL.Text, IDL.Text);
+export const non_tuple = IDL.Record({ _1_ : IDL.Text, _2_ : IDL.Text });
+
+export const idlService = IDL.Service({
+  'bab' : IDL.Func([IDL.Int, IDL.Nat], [], []),
+  'bar' : IDL.Func(
+      [IDL.Record({ '2' : IDL.Int })],
+      [IDL.Variant({ 'e20' : IDL.Null, 'e30' : IDL.Null })],
+      [],
+    ),
+  'bas' : IDL.Func(
+      [IDL.Tuple(IDL.Int, IDL.Int)],
+      [IDL.Tuple(IDL.Text, IDL.Nat)],
+      [],
+    ),
+  'baz' : IDL.Func(
+      [IDL.Record({ _2_ : IDL.Int, '2' : IDL.Nat })],
+      [IDL.Record({})],
+      [],
+    ),
+  'bba' : IDL.Func([tuple], [non_tuple], []),
+  'bib' : IDL.Func([IDL.Tuple(IDL.Int)], [IDL.Variant({ _0_ : IDL.Int })], []),
+  'foo' : IDL.Func(
+      [IDL.Record({ _2_ : IDL.Int })],
+      [IDL.Record({ _2_ : IDL.Int, '_2' : IDL.Int })],
+      [],
+    ),
+});
+
+export const idlInitArgs = [];
+
 export const idlFactory = ({ IDL }) => {
   const tuple = IDL.Tuple(IDL.Text, IDL.Text);
   const non_tuple = IDL.Record({ _1_ : IDL.Text, _2_ : IDL.Text });
+  
   return IDL.Service({
     'bab' : IDL.Func([IDL.Int, IDL.Nat], [], []),
     'bar' : IDL.Func(
@@ -31,4 +65,5 @@ export const idlFactory = ({ IDL }) => {
       ),
   });
 };
+
 export const init = ({ IDL }) => { return []; };
diff --git a/rust/candid_parser/tests/assets/ok/fieldnat.mo b/rust/candid_parser/tests/assets/ok/fieldnat.mo
index 64f771834..f38c0359f 100644
--- a/rust/candid_parser/tests/assets/ok/fieldnat.mo
+++ b/rust/candid_parser/tests/assets/ok/fieldnat.mo
@@ -5,7 +5,7 @@ module {
   public type non_tuple = { _1_  : Text; _2_  : Text };
   public type tuple = (Text, Text);
   public type Self = actor {
-    bab : shared (Int, Nat) -> async ();
+    bab : shared (two : Int, Nat) -> async ();
     bar : shared { _50_ : Int } -> async { #e20; #e30 };
     bas : shared ((Int, Int)) -> async ((Text, Nat));
     baz : shared { _2_  : Int; _50_ : Nat } -> async {};
diff --git a/rust/candid_parser/tests/assets/ok/fieldnat.rs b/rust/candid_parser/tests/assets/ok/fieldnat.rs
index b5399f7f8..55a926045 100644
--- a/rust/candid_parser/tests/assets/ok/fieldnat.rs
+++ b/rust/candid_parser/tests/assets/ok/fieldnat.rs
@@ -17,7 +17,7 @@ pub struct BazArg {
 #[derive(CandidType, Deserialize)]
 pub struct BazRet {}
 #[derive(CandidType, Deserialize)]
-pub struct Tuple (pub String,pub String,);
+pub struct Tuple (pub String, pub String);
 #[derive(CandidType, Deserialize)]
 pub struct NonTuple { pub _1_: String, pub _2_: String }
 #[derive(CandidType, Deserialize)]
@@ -29,13 +29,13 @@ pub struct FooRet { pub _2_: candid::Int, pub _2: candid::Int }
 
 pub struct Service(pub Principal);
 impl Service {
-  pub async fn bab(&self, arg0: &candid::Int, arg1: &candid::Nat) -> Result<()> {
-    ic_cdk::call(self.0, "bab", (arg0,arg1,)).await
+  pub async fn bab(&self, two: &candid::Int, arg1: &candid::Nat) -> Result<()> {
+    ic_cdk::call(self.0, "bab", (two,arg1,)).await
   }
   pub async fn bar(&self, arg0: &BarArg) -> Result<(BarRet,)> {
     ic_cdk::call(self.0, "bar", (arg0,)).await
   }
-  pub async fn bas(&self, arg0: &(candid::Int,candid::Int,)) -> Result<((String,candid::Nat,),)> {
+  pub async fn bas(&self, arg0: &(candid::Int, candid::Int)) -> Result<((String, candid::Nat),)> {
     ic_cdk::call(self.0, "bas", (arg0,)).await
   }
   pub async fn baz(&self, arg0: &BazArg) -> Result<(BazRet,)> {
@@ -44,7 +44,7 @@ impl Service {
   pub async fn bba(&self, arg0: &Tuple) -> Result<(NonTuple,)> {
     ic_cdk::call(self.0, "bba", (arg0,)).await
   }
-  pub async fn bib(&self, arg0: &(candid::Int,)) -> Result<(BibRet,)> {
+  pub async fn bib(&self, arg0: &(candid::Int)) -> Result<(BibRet,)> {
     ic_cdk::call(self.0, "bib", (arg0,)).await
   }
   pub async fn foo(&self, arg0: &FooArg) -> Result<(FooRet,)> {
diff --git a/rust/candid_parser/tests/assets/ok/float.d.ts b/rust/candid_parser/tests/assets/ok/float.d.ts
index d30eecb3f..54cfd6a24 100644
--- a/rust/candid_parser/tests/assets/ok/float.d.ts
+++ b/rust/candid_parser/tests/assets/ok/float.d.ts
@@ -7,5 +7,7 @@ export interface _SERVICE {
   'to_f32' : ActorMethod<[number], number>,
   'to_f64' : ActorMethod<[number], number>,
 }
+export declare const idlService: IDL.ServiceClass;
+export declare const idlInitArgs: IDL.Type[];
 export declare const idlFactory: IDL.InterfaceFactory;
 export declare const init: (args: { IDL: typeof IDL }) => IDL.Type[];
diff --git a/rust/candid_parser/tests/assets/ok/float.js b/rust/candid_parser/tests/assets/ok/float.js
index f44891659..011e5700a 100644
--- a/rust/candid_parser/tests/assets/ok/float.js
+++ b/rust/candid_parser/tests/assets/ok/float.js
@@ -1,3 +1,13 @@
+import { IDL } from '@dfinity/candid';
+
+export const idlService = IDL.Service({
+  'identity32' : IDL.Func([IDL.Float32], [IDL.Float32], []),
+  'to_f32' : IDL.Func([IDL.Float64], [IDL.Float32], []),
+  'to_f64' : IDL.Func([IDL.Float32], [IDL.Float64], []),
+});
+
+export const idlInitArgs = [];
+
 export const idlFactory = ({ IDL }) => {
   return IDL.Service({
     'identity32' : IDL.Func([IDL.Float32], [IDL.Float32], []),
@@ -5,4 +15,5 @@ export const idlFactory = ({ IDL }) => {
     'to_f64' : IDL.Func([IDL.Float32], [IDL.Float64], []),
   });
 };
+
 export const init = ({ IDL }) => { return []; };
diff --git a/rust/candid_parser/tests/assets/ok/inline_methods.d.ts b/rust/candid_parser/tests/assets/ok/inline_methods.d.ts
index cf3951e2c..f3f82eea0 100644
--- a/rust/candid_parser/tests/assets/ok/inline_methods.d.ts
+++ b/rust/candid_parser/tests/assets/ok/inline_methods.d.ts
@@ -23,5 +23,7 @@ export interface _SERVICE {
   'high_order_fn_via_record' : ActorMethod<[R], bigint>,
   'high_order_fn_via_record_inline' : ActorMethod<[RInline], bigint>,
 }
+export declare const idlService: IDL.ServiceClass;
+export declare const idlInitArgs: IDL.Type[];
 export declare const idlFactory: IDL.InterfaceFactory;
 export declare const init: (args: { IDL: typeof IDL }) => IDL.Type[];
diff --git a/rust/candid_parser/tests/assets/ok/inline_methods.js b/rust/candid_parser/tests/assets/ok/inline_methods.js
index 1b63f3979..497784f13 100644
--- a/rust/candid_parser/tests/assets/ok/inline_methods.js
+++ b/rust/candid_parser/tests/assets/ok/inline_methods.js
@@ -1,3 +1,34 @@
+import { IDL } from '@dfinity/candid';
+
+export const Fn = IDL.Func([IDL.Nat], [IDL.Nat], ['query']);
+export const Gn = Fn;
+export const R = IDL.Record({
+  'x' : IDL.Nat,
+  'fn' : Fn,
+  'gn' : Gn,
+  'nested' : IDL.Record({ 'fn' : Gn }),
+});
+export const RInline = IDL.Record({
+  'x' : IDL.Nat,
+  'fn' : IDL.Func([IDL.Nat], [IDL.Nat], ['query']),
+});
+
+export const idlService = IDL.Service({
+  'add_two' : IDL.Func([IDL.Nat], [IDL.Nat], []),
+  'fn' : Fn,
+  'high_order_fn' : IDL.Func([IDL.Nat, Fn], [IDL.Nat], []),
+  'high_order_fn_inline' : IDL.Func(
+      [IDL.Nat, IDL.Func([IDL.Nat], [IDL.Nat], ['query'])],
+      [IDL.Nat],
+      [],
+    ),
+  'high_order_fn_via_id' : IDL.Func([IDL.Nat, Gn], [Fn], []),
+  'high_order_fn_via_record' : IDL.Func([R], [IDL.Nat], []),
+  'high_order_fn_via_record_inline' : IDL.Func([RInline], [IDL.Nat], []),
+});
+
+export const idlInitArgs = [];
+
 export const idlFactory = ({ IDL }) => {
   const Fn = IDL.Func([IDL.Nat], [IDL.Nat], ['query']);
   const Gn = Fn;
@@ -11,6 +42,7 @@ export const idlFactory = ({ IDL }) => {
     'x' : IDL.Nat,
     'fn' : IDL.Func([IDL.Nat], [IDL.Nat], ['query']),
   });
+  
   return IDL.Service({
     'add_two' : IDL.Func([IDL.Nat], [IDL.Nat], []),
     'fn' : Fn,
@@ -25,4 +57,5 @@ export const idlFactory = ({ IDL }) => {
     'high_order_fn_via_record_inline' : IDL.Func([RInline], [IDL.Nat], []),
   });
 };
+
 export const init = ({ IDL }) => { return []; };
diff --git a/rust/candid_parser/tests/assets/ok/inline_methods.mo b/rust/candid_parser/tests/assets/ok/inline_methods.mo
index b1c8b0168..f97f4ecc6 100644
--- a/rust/candid_parser/tests/assets/ok/inline_methods.mo
+++ b/rust/candid_parser/tests/assets/ok/inline_methods.mo
@@ -3,9 +3,9 @@
 
 module {
   public type Fn = shared query Nat -> async Nat;
-  public type Gn = Fn;
   public type R = { x : Nat; fn : Fn; gn : Gn; nested : { fn : Gn } };
   public type RInline = { x : Nat; fn : shared query Nat -> async Nat };
+  public type Gn = Fn;
   public type Self = actor {
     add_two : shared Nat -> async Nat;
     fn : Fn;
diff --git a/rust/candid_parser/tests/assets/ok/keyword.d.ts b/rust/candid_parser/tests/assets/ok/keyword.d.ts
index 8e2c0aa6c..0df86b31e 100644
--- a/rust/candid_parser/tests/assets/ok/keyword.d.ts
+++ b/rust/candid_parser/tests/assets/ok/keyword.d.ts
@@ -31,5 +31,7 @@ export interface _SERVICE {
     undefined
   >,
 }
+export declare const idlService: IDL.ServiceClass;
+export declare const idlInitArgs: IDL.Type[];
 export declare const idlFactory: IDL.InterfaceFactory;
 export declare const init: (args: { IDL: typeof IDL }) => IDL.Type[];
diff --git a/rust/candid_parser/tests/assets/ok/keyword.did b/rust/candid_parser/tests/assets/ok/keyword.did
index 0a42d407c..9b1d2cec1 100644
--- a/rust/candid_parser/tests/assets/ok/keyword.did
+++ b/rust/candid_parser/tests/assets/ok/keyword.did
@@ -6,7 +6,7 @@ type if = variant {
   leaf : int;
 };
 type return = service { f : t; g : (list) -> (if, stream) };
-type t = func (return) -> ();
+type t = func (server : return) -> ();
 type stream = opt record { head : nat; next : func () -> (stream) query };
 service : {
   Oneway : () -> () oneway;
diff --git a/rust/candid_parser/tests/assets/ok/keyword.js b/rust/candid_parser/tests/assets/ok/keyword.js
index 032fe5f2a..a98f142c8 100644
--- a/rust/candid_parser/tests/assets/ok/keyword.js
+++ b/rust/candid_parser/tests/assets/ok/keyword.js
@@ -1,3 +1,69 @@
+import { IDL } from '@dfinity/candid';
+
+export const if_ = IDL.Rec();
+export const list = IDL.Rec();
+export const o = IDL.Rec();
+export const stream = IDL.Rec();
+export const t = IDL.Rec();
+o.fill(IDL.Opt(o));
+export const node = IDL.Record({ 'head' : IDL.Nat, 'tail' : list });
+list.fill(IDL.Opt(node));
+if_.fill(
+  IDL.Variant({
+    'branch' : IDL.Record({ 'val' : IDL.Int, 'left' : if_, 'right' : if_ }),
+    'leaf' : IDL.Int,
+  })
+);
+stream.fill(
+  IDL.Opt(
+    IDL.Record({ 'head' : IDL.Nat, 'next' : IDL.Func([], [stream], ['query']) })
+  )
+);
+export const return_ = IDL.Service({
+  'f' : t,
+  'g' : IDL.Func([list], [if_, stream], []),
+});
+t.fill(IDL.Func([return_], [], []));
+
+export const idlService = IDL.Service({
+  'Oneway' : IDL.Func([], [], ['oneway']),
+  'f_' : IDL.Func([o], [o], []),
+  'field' : IDL.Func(
+      [IDL.Record({ 'test' : IDL.Nat16, _1291438163_ : IDL.Nat8 })],
+      [IDL.Record({})],
+      [],
+    ),
+  'fieldnat' : IDL.Func(
+      [IDL.Record({ _2_ : IDL.Int, '2' : IDL.Nat })],
+      [IDL.Tuple(IDL.Int)],
+      [],
+    ),
+  'oneway' : IDL.Func([IDL.Nat8], [], ['oneway']),
+  'oneway_' : IDL.Func([IDL.Nat8], [], ['oneway']),
+  'query' : IDL.Func([IDL.Vec(IDL.Nat8)], [IDL.Vec(IDL.Nat8)], ['query']),
+  'return' : IDL.Func([o], [o], []),
+  'service' : t,
+  'tuple' : IDL.Func(
+      [IDL.Tuple(IDL.Int, IDL.Vec(IDL.Nat8), IDL.Text)],
+      [IDL.Tuple(IDL.Int, IDL.Nat8)],
+      [],
+    ),
+  'variant' : IDL.Func(
+      [
+        IDL.Variant({
+          'A' : IDL.Null,
+          'B' : IDL.Null,
+          'C' : IDL.Null,
+          'D' : IDL.Float64,
+        }),
+      ],
+      [],
+      [],
+    ),
+});
+
+export const idlInitArgs = [];
+
 export const idlFactory = ({ IDL }) => {
   const if_ = IDL.Rec();
   const list = IDL.Rec();
@@ -26,6 +92,7 @@ export const idlFactory = ({ IDL }) => {
     'g' : IDL.Func([list], [if_, stream], []),
   });
   t.fill(IDL.Func([return_], [], []));
+  
   return IDL.Service({
     'Oneway' : IDL.Func([], [], ['oneway']),
     'f_' : IDL.Func([o], [o], []),
@@ -63,4 +130,5 @@ export const idlFactory = ({ IDL }) => {
       ),
   });
 };
+
 export const init = ({ IDL }) => { return []; };
diff --git a/rust/candid_parser/tests/assets/ok/keyword.mo b/rust/candid_parser/tests/assets/ok/keyword.mo
index 2802968e2..cf214b121 100644
--- a/rust/candid_parser/tests/assets/ok/keyword.mo
+++ b/rust/candid_parser/tests/assets/ok/keyword.mo
@@ -2,16 +2,16 @@
 // Please use `import service "ic:canister_id"` instead to call canisters on the IC if possible.
 
 module {
+  public type stream = ?{ head : Nat; next : shared query () -> async stream };
   public type if_ = {
     #branch : { val : Int; left : if_; right : if_ };
     #leaf : Int;
   };
+  public type return_ = actor { f : t; g : shared list -> async (if_, stream) };
   public type list = ?node;
-  public type node = { head : Nat; tail : list };
   public type o = ?o;
-  public type return_ = actor { f : t; g : shared list -> async (if_, stream) };
-  public type stream = ?{ head : Nat; next : shared query () -> async stream };
-  public type t = shared return_ -> async ();
+  public type t = shared (server : return_) -> async ();
+  public type node = { head : Nat; tail : list };
   public type Self = actor {
     Oneway : shared () -> ();
     f__ : shared o -> async o;
diff --git a/rust/candid_parser/tests/assets/ok/keyword.rs b/rust/candid_parser/tests/assets/ok/keyword.rs
index 86e2a4c4e..086f853e4 100644
--- a/rust/candid_parser/tests/assets/ok/keyword.rs
+++ b/rust/candid_parser/tests/assets/ok/keyword.rs
@@ -51,7 +51,7 @@ impl Service {
   pub async fn field(&self, arg0: &FieldArg) -> Result<(FieldRet,)> {
     ic_cdk::call(self.0, "field", (arg0,)).await
   }
-  pub async fn fieldnat(&self, arg0: &FieldnatArg) -> Result<((candid::Int,),)> {
+  pub async fn fieldnat(&self, arg0: &FieldnatArg) -> Result<((candid::Int),)> {
     ic_cdk::call(self.0, "fieldnat", (arg0,)).await
   }
   pub async fn oneway(&self, arg0: &u8) -> Result<()> {
@@ -66,10 +66,10 @@ impl Service {
   pub async fn r#return(&self, arg0: &O) -> Result<(O,)> {
     ic_cdk::call(self.0, "return", (arg0,)).await
   }
-  pub async fn service(&self, arg0: &Return) -> Result<()> {
-    ic_cdk::call(self.0, "service", (arg0,)).await
+  pub async fn service(&self, server: &Return) -> Result<()> {
+    ic_cdk::call(self.0, "service", (server,)).await
   }
-  pub async fn tuple(&self, arg0: &(candid::Int,serde_bytes::ByteBuf,String,)) -> Result<((candid::Int,u8,),)> {
+  pub async fn tuple(&self, arg0: &(candid::Int, serde_bytes::ByteBuf, String)) -> Result<((candid::Int, u8),)> {
     ic_cdk::call(self.0, "tuple", (arg0,)).await
   }
   pub async fn variant(&self, arg0: &VariantArg) -> Result<()> {
diff --git a/rust/candid_parser/tests/assets/ok/malicious_doc.d.ts b/rust/candid_parser/tests/assets/ok/malicious_doc.d.ts
index f613779f8..7491955ba 100644
--- a/rust/candid_parser/tests/assets/ok/malicious_doc.d.ts
+++ b/rust/candid_parser/tests/assets/ok/malicious_doc.d.ts
@@ -22,5 +22,7 @@ export interface _SERVICE {
    */
   'get' : ActorMethod<[], MaliciousType>,
 }
+export declare const idlService: IDL.ServiceClass;
+export declare const idlInitArgs: IDL.Type[];
 export declare const idlFactory: IDL.InterfaceFactory;
 export declare const init: (args: { IDL: typeof IDL }) => IDL.Type[];
diff --git a/rust/candid_parser/tests/assets/ok/malicious_doc.js b/rust/candid_parser/tests/assets/ok/malicious_doc.js
index ff18f8ed1..552475ffe 100644
--- a/rust/candid_parser/tests/assets/ok/malicious_doc.js
+++ b/rust/candid_parser/tests/assets/ok/malicious_doc.js
@@ -1,5 +1,17 @@
+import { IDL } from '@dfinity/candid';
+
+export const MaliciousType = IDL.Record({ 'field' : IDL.Text });
+
+export const idlService = IDL.Service({
+  'get' : IDL.Func([], [MaliciousType], ['query']),
+});
+
+export const idlInitArgs = [];
+
 export const idlFactory = ({ IDL }) => {
   const MaliciousType = IDL.Record({ 'field' : IDL.Text });
+  
   return IDL.Service({ 'get' : IDL.Func([], [MaliciousType], ['query']) });
 };
+
 export const init = ({ IDL }) => { return []; };
diff --git a/rust/candid_parser/tests/assets/ok/management.d.ts b/rust/candid_parser/tests/assets/ok/management.d.ts
index 8cf54f90a..c49b43676 100644
--- a/rust/candid_parser/tests/assets/ok/management.d.ts
+++ b/rust/candid_parser/tests/assets/ok/management.d.ts
@@ -171,5 +171,7 @@ export interface _SERVICE {
     undefined
   >,
 }
+export declare const idlService: IDL.ServiceClass;
+export declare const idlInitArgs: IDL.Type[];
 export declare const idlFactory: IDL.InterfaceFactory;
 export declare const init: (args: { IDL: typeof IDL }) => IDL.Type[];
diff --git a/rust/candid_parser/tests/assets/ok/management.js b/rust/candid_parser/tests/assets/ok/management.js
index cb2b784b3..29817e94f 100644
--- a/rust/candid_parser/tests/assets/ok/management.js
+++ b/rust/candid_parser/tests/assets/ok/management.js
@@ -1,3 +1,235 @@
+import { IDL } from '@dfinity/candid';
+
+export const bitcoin_network = IDL.Variant({
+  'mainnet' : IDL.Null,
+  'testnet' : IDL.Null,
+});
+export const bitcoin_address = IDL.Text;
+export const get_balance_request = IDL.Record({
+  'network' : bitcoin_network,
+  'address' : bitcoin_address,
+  'min_confirmations' : IDL.Opt(IDL.Nat32),
+});
+export const satoshi = IDL.Nat64;
+export const get_current_fee_percentiles_request = IDL.Record({
+  'network' : bitcoin_network,
+});
+export const millisatoshi_per_byte = IDL.Nat64;
+export const get_utxos_request = IDL.Record({
+  'network' : bitcoin_network,
+  'filter' : IDL.Opt(
+    IDL.Variant({ 'page' : IDL.Vec(IDL.Nat8), 'min_confirmations' : IDL.Nat32 })
+  ),
+  'address' : bitcoin_address,
+});
+export const block_hash = IDL.Vec(IDL.Nat8);
+export const outpoint = IDL.Record({
+  'txid' : IDL.Vec(IDL.Nat8),
+  'vout' : IDL.Nat32,
+});
+export const utxo = IDL.Record({
+  'height' : IDL.Nat32,
+  'value' : satoshi,
+  'outpoint' : outpoint,
+});
+export const get_utxos_response = IDL.Record({
+  'next_page' : IDL.Opt(IDL.Vec(IDL.Nat8)),
+  'tip_height' : IDL.Nat32,
+  'tip_block_hash' : block_hash,
+  'utxos' : IDL.Vec(utxo),
+});
+export const send_transaction_request = IDL.Record({
+  'transaction' : IDL.Vec(IDL.Nat8),
+  'network' : bitcoin_network,
+});
+export const canister_id = IDL.Principal;
+export const definite_canister_settings = IDL.Record({
+  'freezing_threshold' : IDL.Nat,
+  'controllers' : IDL.Vec(IDL.Principal),
+  'memory_allocation' : IDL.Nat,
+  'compute_allocation' : IDL.Nat,
+});
+export const canister_settings = IDL.Record({
+  'freezing_threshold' : IDL.Opt(IDL.Nat),
+  'controllers' : IDL.Opt(IDL.Vec(IDL.Principal)),
+  'memory_allocation' : IDL.Opt(IDL.Nat),
+  'compute_allocation' : IDL.Opt(IDL.Nat),
+});
+export const ecdsa_curve = IDL.Variant({ 'secp256k1' : IDL.Null });
+export const http_header = IDL.Record({
+  'value' : IDL.Text,
+  'name' : IDL.Text,
+});
+export const http_response = IDL.Record({
+  'status' : IDL.Nat,
+  'body' : IDL.Vec(IDL.Nat8),
+  'headers' : IDL.Vec(http_header),
+});
+export const wasm_module = IDL.Vec(IDL.Nat8);
+
+export const idlService = IDL.Service({
+  'bitcoin_get_balance' : IDL.Func([get_balance_request], [satoshi], []),
+  'bitcoin_get_current_fee_percentiles' : IDL.Func(
+      [get_current_fee_percentiles_request],
+      [IDL.Vec(millisatoshi_per_byte)],
+      [],
+    ),
+  'bitcoin_get_utxos' : IDL.Func([get_utxos_request], [get_utxos_response], []),
+  'bitcoin_send_transaction' : IDL.Func([send_transaction_request], [], []),
+  'canister_status' : IDL.Func(
+      [IDL.Record({ 'canister_id' : canister_id })],
+      [
+        IDL.Record({
+          'status' : IDL.Variant({
+            'stopped' : IDL.Null,
+            'stopping' : IDL.Null,
+            'running' : IDL.Null,
+          }),
+          'memory_size' : IDL.Nat,
+          'cycles' : IDL.Nat,
+          'settings' : definite_canister_settings,
+          'idle_cycles_burned_per_day' : IDL.Nat,
+          'module_hash' : IDL.Opt(IDL.Vec(IDL.Nat8)),
+        }),
+      ],
+      [],
+    ),
+  'create_canister' : IDL.Func(
+      [IDL.Record({ 'settings' : IDL.Opt(canister_settings) })],
+      [IDL.Record({ 'canister_id' : canister_id })],
+      [],
+    ),
+  'delete_canister' : IDL.Func(
+      [IDL.Record({ 'canister_id' : canister_id })],
+      [],
+      [],
+    ),
+  'deposit_cycles' : IDL.Func(
+      [IDL.Record({ 'canister_id' : canister_id })],
+      [],
+      [],
+    ),
+  'ecdsa_public_key' : IDL.Func(
+      [
+        IDL.Record({
+          'key_id' : IDL.Record({ 'name' : IDL.Text, 'curve' : ecdsa_curve }),
+          'canister_id' : IDL.Opt(canister_id),
+          'derivation_path' : IDL.Vec(IDL.Vec(IDL.Nat8)),
+        }),
+      ],
+      [
+        IDL.Record({
+          'public_key' : IDL.Vec(IDL.Nat8),
+          'chain_code' : IDL.Vec(IDL.Nat8),
+        }),
+      ],
+      [],
+    ),
+  'http_request' : IDL.Func(
+      [
+        IDL.Record({
+          'url' : IDL.Text,
+          'method' : IDL.Variant({
+            'get' : IDL.Null,
+            'head' : IDL.Null,
+            'post' : IDL.Null,
+          }),
+          'max_response_bytes' : IDL.Opt(IDL.Nat64),
+          'body' : IDL.Opt(IDL.Vec(IDL.Nat8)),
+          'transform' : IDL.Opt(
+            IDL.Record({
+              'function' : IDL.Func(
+                  [
+                    IDL.Record({
+                      'context' : IDL.Vec(IDL.Nat8),
+                      'response' : http_response,
+                    }),
+                  ],
+                  [http_response],
+                  ['query'],
+                ),
+              'context' : IDL.Vec(IDL.Nat8),
+            })
+          ),
+          'headers' : IDL.Vec(http_header),
+        }),
+      ],
+      [http_response],
+      [],
+    ),
+  'install_code' : IDL.Func(
+      [
+        IDL.Record({
+          'arg' : IDL.Vec(IDL.Nat8),
+          'wasm_module' : wasm_module,
+          'mode' : IDL.Variant({
+            'reinstall' : IDL.Null,
+            'upgrade' : IDL.Null,
+            'install' : IDL.Null,
+          }),
+          'canister_id' : canister_id,
+        }),
+      ],
+      [],
+      [],
+    ),
+  'provisional_create_canister_with_cycles' : IDL.Func(
+      [
+        IDL.Record({
+          'settings' : IDL.Opt(canister_settings),
+          'specified_id' : IDL.Opt(canister_id),
+          'amount' : IDL.Opt(IDL.Nat),
+        }),
+      ],
+      [IDL.Record({ 'canister_id' : canister_id })],
+      [],
+    ),
+  'provisional_top_up_canister' : IDL.Func(
+      [IDL.Record({ 'canister_id' : canister_id, 'amount' : IDL.Nat })],
+      [],
+      [],
+    ),
+  'raw_rand' : IDL.Func([], [IDL.Vec(IDL.Nat8)], []),
+  'sign_with_ecdsa' : IDL.Func(
+      [
+        IDL.Record({
+          'key_id' : IDL.Record({ 'name' : IDL.Text, 'curve' : ecdsa_curve }),
+          'derivation_path' : IDL.Vec(IDL.Vec(IDL.Nat8)),
+          'message_hash' : IDL.Vec(IDL.Nat8),
+        }),
+      ],
+      [IDL.Record({ 'signature' : IDL.Vec(IDL.Nat8) })],
+      [],
+    ),
+  'start_canister' : IDL.Func(
+      [IDL.Record({ 'canister_id' : canister_id })],
+      [],
+      [],
+    ),
+  'stop_canister' : IDL.Func(
+      [IDL.Record({ 'canister_id' : canister_id })],
+      [],
+      [],
+    ),
+  'uninstall_code' : IDL.Func(
+      [IDL.Record({ 'canister_id' : canister_id })],
+      [],
+      [],
+    ),
+  'update_settings' : IDL.Func(
+      [
+        IDL.Record({
+          'canister_id' : IDL.Principal,
+          'settings' : canister_settings,
+        }),
+      ],
+      [],
+      [],
+    ),
+});
+
+export const idlInitArgs = [];
+
 export const idlFactory = ({ IDL }) => {
   const bitcoin_network = IDL.Variant({
     'mainnet' : IDL.Null,
@@ -65,6 +297,7 @@ export const idlFactory = ({ IDL }) => {
     'headers' : IDL.Vec(http_header),
   });
   const wasm_module = IDL.Vec(IDL.Nat8);
+  
   return IDL.Service({
     'bitcoin_get_balance' : IDL.Func([get_balance_request], [satoshi], []),
     'bitcoin_get_current_fee_percentiles' : IDL.Func(
@@ -230,4 +463,5 @@ export const idlFactory = ({ IDL }) => {
       ),
   });
 };
+
 export const init = ({ IDL }) => { return []; };
diff --git a/rust/candid_parser/tests/assets/ok/management.mo b/rust/candid_parser/tests/assets/ok/management.mo
index 0609c7387..83fc90749 100644
--- a/rust/candid_parser/tests/assets/ok/management.mo
+++ b/rust/candid_parser/tests/assets/ok/management.mo
@@ -3,34 +3,41 @@
 
 module {
   public type bitcoin_address = Text;
-  public type bitcoin_network = { #mainnet; #testnet };
-  public type block_hash = Blob;
-  public type canister_id = Principal;
+  public type ecdsa_curve = { #secp256k1 };
+  public type get_utxos_request = {
+    network : bitcoin_network;
+    filter : ?{ #page : Blob; #min_confirmations : Nat32 };
+    address : bitcoin_address;
+  };
   public type canister_settings = {
     freezing_threshold : ?Nat;
     controllers : ?[Principal];
     memory_allocation : ?Nat;
     compute_allocation : ?Nat;
   };
-  public type definite_canister_settings = {
-    freezing_threshold : Nat;
-    controllers : [Principal];
-    memory_allocation : Nat;
-    compute_allocation : Nat;
+  public type user_id = Principal;
+  public type get_current_fee_percentiles_request = {
+    network : bitcoin_network;
   };
-  public type ecdsa_curve = { #secp256k1 };
+  public type outpoint = { txid : Blob; vout : Nat32 };
   public type get_balance_request = {
     network : bitcoin_network;
     address : bitcoin_address;
     min_confirmations : ?Nat32;
   };
-  public type get_current_fee_percentiles_request = {
-    network : bitcoin_network;
+  public type definite_canister_settings = {
+    freezing_threshold : Nat;
+    controllers : [Principal];
+    memory_allocation : Nat;
+    compute_allocation : Nat;
   };
-  public type get_utxos_request = {
+  public type satoshi = Nat64;
+  public type bitcoin_network = { #mainnet; #testnet };
+  public type millisatoshi_per_byte = Nat64;
+  public type wasm_module = Blob;
+  public type send_transaction_request = {
+    transaction : Blob;
     network : bitcoin_network;
-    filter : ?{ #page : Blob; #min_confirmations : Nat32 };
-    address : bitcoin_address;
   };
   public type get_utxos_response = {
     next_page : ?Blob;
@@ -38,22 +45,15 @@ module {
     tip_block_hash : block_hash;
     utxos : [utxo];
   };
-  public type http_header = { value : Text; name : Text };
+  public type block_hash = Blob;
+  public type canister_id = Principal;
+  public type utxo = { height : Nat32; value : satoshi; outpoint : outpoint };
   public type http_response = {
     status : Nat;
     body : Blob;
     headers : [http_header];
   };
-  public type millisatoshi_per_byte = Nat64;
-  public type outpoint = { txid : Blob; vout : Nat32 };
-  public type satoshi = Nat64;
-  public type send_transaction_request = {
-    transaction : Blob;
-    network : bitcoin_network;
-  };
-  public type user_id = Principal;
-  public type utxo = { height : Nat32; value : satoshi; outpoint : outpoint };
-  public type wasm_module = Blob;
+  public type http_header = { value : Text; name : Text };
   public type Self = actor {
     bitcoin_get_balance : shared get_balance_request -> async satoshi;
     bitcoin_get_current_fee_percentiles : shared get_current_fee_percentiles_request -> async [
diff --git a/rust/candid_parser/tests/assets/ok/recursion.d.ts b/rust/candid_parser/tests/assets/ok/recursion.d.ts
index 2f0a0f626..36368cbea 100644
--- a/rust/candid_parser/tests/assets/ok/recursion.d.ts
+++ b/rust/candid_parser/tests/assets/ok/recursion.d.ts
@@ -17,5 +17,7 @@ export type tree = {
   } |
   { 'leaf' : bigint };
 export interface _SERVICE extends s {}
+export declare const idlService: IDL.ServiceClass;
+export declare const idlInitArgs: IDL.Type[];
 export declare const idlFactory: IDL.InterfaceFactory;
 export declare const init: (args: { IDL: typeof IDL }) => IDL.Type[];
diff --git a/rust/candid_parser/tests/assets/ok/recursion.did b/rust/candid_parser/tests/assets/ok/recursion.did
index 9137077e8..4dd70d2e7 100644
--- a/rust/candid_parser/tests/assets/ok/recursion.did
+++ b/rust/candid_parser/tests/assets/ok/recursion.did
@@ -8,6 +8,6 @@ type tree = variant {
 };
 // Doc comment for service id
 type s = service { f : t; g : (list) -> (B, tree, stream) };
-type t = func (s) -> ();
+type t = func (server : s) -> ();
 type stream = opt record { head : nat; next : func () -> (stream) query };
 service : s
diff --git a/rust/candid_parser/tests/assets/ok/recursion.js b/rust/candid_parser/tests/assets/ok/recursion.js
index d0fdaeee8..95d11d847 100644
--- a/rust/candid_parser/tests/assets/ok/recursion.js
+++ b/rust/candid_parser/tests/assets/ok/recursion.js
@@ -1,3 +1,32 @@
+import { IDL } from '@dfinity/candid';
+
+export const B = IDL.Rec();
+export const list = IDL.Rec();
+export const s = IDL.Rec();
+export const stream = IDL.Rec();
+export const tree = IDL.Rec();
+export const t = IDL.Func([s], [], []);
+export const node = IDL.Record({ 'head' : IDL.Nat, 'tail' : list });
+list.fill(IDL.Opt(node));
+export const A = B;
+B.fill(IDL.Opt(A));
+tree.fill(
+  IDL.Variant({
+    'branch' : IDL.Record({ 'val' : IDL.Int, 'left' : tree, 'right' : tree }),
+    'leaf' : IDL.Int,
+  })
+);
+stream.fill(
+  IDL.Opt(
+    IDL.Record({ 'head' : IDL.Nat, 'next' : IDL.Func([], [stream], ['query']) })
+  )
+);
+s.fill(IDL.Service({ 'f' : t, 'g' : IDL.Func([list], [B, tree, stream], []) }));
+
+export const idlService = s.getType();
+
+export const idlInitArgs = [];
+
 export const idlFactory = ({ IDL }) => {
   const B = IDL.Rec();
   const list = IDL.Rec();
@@ -26,6 +55,8 @@ export const idlFactory = ({ IDL }) => {
   s.fill(
     IDL.Service({ 'f' : t, 'g' : IDL.Func([list], [B, tree, stream], []) })
   );
+  
   return s.getType();
 };
+
 export const init = ({ IDL }) => { return []; };
diff --git a/rust/candid_parser/tests/assets/ok/recursion.mo b/rust/candid_parser/tests/assets/ok/recursion.mo
index cdb3eb519..34e72f02b 100644
--- a/rust/candid_parser/tests/assets/ok/recursion.mo
+++ b/rust/candid_parser/tests/assets/ok/recursion.mo
@@ -2,17 +2,17 @@
 // Please use `import service "ic:canister_id"` instead to call canisters on the IC if possible.
 
 module {
+  public type stream = ?{ head : Nat; next : shared query () -> async stream };
   public type A = B;
-  public type B = ?A;
-  public type list = ?node;
-  public type node = { head : Nat; tail : list };
   /// Doc comment for service id
   public type s = actor { f : t; g : shared list -> async (B, tree, stream) };
-  public type stream = ?{ head : Nat; next : shared query () -> async stream };
-  public type t = shared s -> async ();
+  public type B = ?A;
+  public type list = ?node;
   public type tree = {
     #branch : { val : Int; left : tree; right : tree };
     #leaf : Int;
   };
+  public type t = shared (server : s) -> async ();
+  public type node = { head : Nat; tail : list };
   public type Self = s
 }
diff --git a/rust/candid_parser/tests/assets/ok/recursion.rs b/rust/candid_parser/tests/assets/ok/recursion.rs
index 3b21c9c3e..239310042 100644
--- a/rust/candid_parser/tests/assets/ok/recursion.rs
+++ b/rust/candid_parser/tests/assets/ok/recursion.rs
@@ -31,8 +31,8 @@ candid::define_service!(pub S : {
 
 pub struct Service(pub Principal);
 impl Service {
-  pub async fn f(&self, arg0: &S) -> Result<()> {
-    ic_cdk::call(self.0, "f", (arg0,)).await
+  pub async fn f(&self, server: &S) -> Result<()> {
+    ic_cdk::call(self.0, "f", (server,)).await
   }
   pub async fn g(&self, arg0: &List) -> Result<(B,Tree,Stream,)> {
     ic_cdk::call(self.0, "g", (arg0,)).await
diff --git a/rust/candid_parser/tests/assets/ok/recursive_class.d.ts b/rust/candid_parser/tests/assets/ok/recursive_class.d.ts
index 546910492..373f7d527 100644
--- a/rust/candid_parser/tests/assets/ok/recursive_class.d.ts
+++ b/rust/candid_parser/tests/assets/ok/recursive_class.d.ts
@@ -4,5 +4,7 @@ import type { IDL } from '@icp-sdk/core/candid';
 
 export interface s { 'next' : ActorMethod<[], Principal> }
 export interface _SERVICE extends s {}
+export declare const idlService: IDL.ServiceClass;
+export declare const idlInitArgs: IDL.Type[];
 export declare const idlFactory: IDL.InterfaceFactory;
 export declare const init: (args: { IDL: typeof IDL }) => IDL.Type[];
diff --git a/rust/candid_parser/tests/assets/ok/recursive_class.js b/rust/candid_parser/tests/assets/ok/recursive_class.js
index a60a6487b..2d83bf276 100644
--- a/rust/candid_parser/tests/assets/ok/recursive_class.js
+++ b/rust/candid_parser/tests/assets/ok/recursive_class.js
@@ -1,10 +1,22 @@
+import { IDL } from '@dfinity/candid';
+
+export const s = IDL.Rec();
+s.fill(IDL.Service({ 'next' : IDL.Func([], [s], []) }));
+
+export const idlService = s.getType();
+
+export const idlInitArgs = [s];
+
 export const idlFactory = ({ IDL }) => {
   const s = IDL.Rec();
   s.fill(IDL.Service({ 'next' : IDL.Func([], [s], []) }));
+  
   return s.getType();
 };
+
 export const init = ({ IDL }) => {
   const s = IDL.Rec();
   s.fill(IDL.Service({ 'next' : IDL.Func([], [s], []) }));
+  
   return [s];
 };
diff --git a/rust/candid_parser/tests/assets/ok/service.d.ts b/rust/candid_parser/tests/assets/ok/service.d.ts
index aea67cd85..b5b415749 100644
--- a/rust/candid_parser/tests/assets/ok/service.d.ts
+++ b/rust/candid_parser/tests/assets/ok/service.d.ts
@@ -18,5 +18,7 @@ export interface _SERVICE {
       { 'b' : { 'f' : [] | [[Principal, string]] } }
   >,
 }
+export declare const idlService: IDL.ServiceClass;
+export declare const idlInitArgs: IDL.Type[];
 export declare const idlFactory: IDL.InterfaceFactory;
 export declare const init: (args: { IDL: typeof IDL }) => IDL.Type[];
diff --git a/rust/candid_parser/tests/assets/ok/service.did b/rust/candid_parser/tests/assets/ok/service.did
index 7dc21afac..741e020cc 100644
--- a/rust/candid_parser/tests/assets/ok/service.did
+++ b/rust/candid_parser/tests/assets/ok/service.did
@@ -3,7 +3,7 @@ type Service2 = Service;
 type Func = func () -> (Service);
 service : {
   asArray : () -> (vec Service2, vec Func) query;
-  asPrincipal : () -> (Service2, Func);
+  asPrincipal : () -> (ret0 : Service2, ret1 : Func);
   asRecord : () -> (record { Service2; opt Service; Func });
   asVariant : () -> (variant { a : Service2; b : record { f : opt Func } });
 }
diff --git a/rust/candid_parser/tests/assets/ok/service.js b/rust/candid_parser/tests/assets/ok/service.js
index e7d8ffd37..9c937bc15 100644
--- a/rust/candid_parser/tests/assets/ok/service.js
+++ b/rust/candid_parser/tests/assets/ok/service.js
@@ -1,8 +1,34 @@
+import { IDL } from '@dfinity/candid';
+
+export const Service = IDL.Rec();
+export const Func = IDL.Func([], [Service], []);
+Service.fill(IDL.Service({ 'f' : Func }));
+export const Service2 = Service;
+
+export const idlService = IDL.Service({
+  'asArray' : IDL.Func([], [IDL.Vec(Service2), IDL.Vec(Func)], ['query']),
+  'asPrincipal' : IDL.Func([], [Service2, Func], []),
+  'asRecord' : IDL.Func([], [IDL.Tuple(Service2, IDL.Opt(Service), Func)], []),
+  'asVariant' : IDL.Func(
+      [],
+      [
+        IDL.Variant({
+          'a' : Service2,
+          'b' : IDL.Record({ 'f' : IDL.Opt(Func) }),
+        }),
+      ],
+      [],
+    ),
+});
+
+export const idlInitArgs = [];
+
 export const idlFactory = ({ IDL }) => {
   const Service = IDL.Rec();
   const Func = IDL.Func([], [Service], []);
   Service.fill(IDL.Service({ 'f' : Func }));
   const Service2 = Service;
+  
   return IDL.Service({
     'asArray' : IDL.Func([], [IDL.Vec(Service2), IDL.Vec(Func)], ['query']),
     'asPrincipal' : IDL.Func([], [Service2, Func], []),
@@ -23,4 +49,5 @@ export const idlFactory = ({ IDL }) => {
       ),
   });
 };
+
 export const init = ({ IDL }) => { return []; };
diff --git a/rust/candid_parser/tests/assets/ok/service.mo b/rust/candid_parser/tests/assets/ok/service.mo
index 14ee15e7a..ff6c34865 100644
--- a/rust/candid_parser/tests/assets/ok/service.mo
+++ b/rust/candid_parser/tests/assets/ok/service.mo
@@ -2,8 +2,8 @@
 // Please use `import service "ic:canister_id"` instead to call canisters on the IC if possible.
 
 module {
-  public type Func = shared () -> async Service;
   public type Service = actor { f : Func };
+  public type Func = shared () -> async Service;
   public type Service2 = Service;
   public type Self = actor {
     asArray : shared query () -> async ([Service2], [Func]);
diff --git a/rust/candid_parser/tests/assets/ok/service.rs b/rust/candid_parser/tests/assets/ok/service.rs
index cbcf60cd7..692b444b7 100644
--- a/rust/candid_parser/tests/assets/ok/service.rs
+++ b/rust/candid_parser/tests/assets/ok/service.rs
@@ -23,7 +23,7 @@ impl Service {
   pub async fn as_principal(&self) -> Result<(Service2,Func,)> {
     ic_cdk::call(self.0, "asPrincipal", ()).await
   }
-  pub async fn as_record(&self) -> Result<((Service2,Option<Service>,Func,),)> {
+  pub async fn as_record(&self) -> Result<((Service2, Option<Service>, Func),)> {
     ic_cdk::call(self.0, "asRecord", ()).await
   }
   pub async fn as_variant(&self) -> Result<(AsVariantRet,)> {
diff --git a/rust/candid_parser/tests/assets/ok/unicode.d.ts b/rust/candid_parser/tests/assets/ok/unicode.d.ts
index e9833d02e..6944f36d0 100644
--- a/rust/candid_parser/tests/assets/ok/unicode.d.ts
+++ b/rust/candid_parser/tests/assets/ok/unicode.d.ts
@@ -18,5 +18,7 @@ export interface _SERVICE {
   '函数名' : ActorMethod<[A], B>,
   '👀' : ActorMethod<[bigint], bigint>,
 }
+export declare const idlService: IDL.ServiceClass;
+export declare const idlInitArgs: IDL.Type[];
 export declare const idlFactory: IDL.InterfaceFactory;
 export declare const init: (args: { IDL: typeof IDL }) => IDL.Type[];
diff --git a/rust/candid_parser/tests/assets/ok/unicode.js b/rust/candid_parser/tests/assets/ok/unicode.js
index 9d9774fb0..c97d46f52 100644
--- a/rust/candid_parser/tests/assets/ok/unicode.js
+++ b/rust/candid_parser/tests/assets/ok/unicode.js
@@ -1,3 +1,27 @@
+import { IDL } from '@dfinity/candid';
+
+export const A = IDL.Record({
+  '\u{e000}' : IDL.Nat,
+  '📦🍦' : IDL.Nat,
+  '字段名' : IDL.Nat,
+  '字 段 名2' : IDL.Nat,
+});
+export const B = IDL.Variant({
+  '' : IDL.Null,
+  '空的' : IDL.Null,
+  '  空的  ' : IDL.Null,
+  '1⃣️2⃣️3⃣️' : IDL.Null,
+});
+
+export const idlService = IDL.Service({
+  '' : IDL.Func([IDL.Nat], [IDL.Nat], []),
+  '✈️  🚗 ⛱️ ' : IDL.Func([], [], ['oneway']),
+  '函数名' : IDL.Func([A], [B], []),
+  '👀' : IDL.Func([IDL.Nat], [IDL.Nat], ['query']),
+});
+
+export const idlInitArgs = [];
+
 export const idlFactory = ({ IDL }) => {
   const A = IDL.Record({
     '\u{e000}' : IDL.Nat,
@@ -11,6 +35,7 @@ export const idlFactory = ({ IDL }) => {
     '  空的  ' : IDL.Null,
     '1⃣️2⃣️3⃣️' : IDL.Null,
   });
+  
   return IDL.Service({
     '' : IDL.Func([IDL.Nat], [IDL.Nat], []),
     '✈️  🚗 ⛱️ ' : IDL.Func([], [], ['oneway']),
@@ -18,4 +43,5 @@ export const idlFactory = ({ IDL }) => {
     '👀' : IDL.Func([IDL.Nat], [IDL.Nat], ['query']),
   });
 };
+
 export const init = ({ IDL }) => { return []; };
diff --git a/rust/candid_parser/tests/assets/service.did b/rust/candid_parser/tests/assets/service.did
index cfec74e3f..43e2602bc 100644
--- a/rust/candid_parser/tests/assets/service.did
+++ b/rust/candid_parser/tests/assets/service.did
@@ -5,5 +5,5 @@ service : {
   asArray: () -> (vec Service2, vec Func) query;
   asRecord: () -> (record { Service2; opt Service; Func });
   asVariant: () -> (variant { a: Service2; b: record { f:opt Func }});
-  asPrincipal: () -> (Service2, Func);
+  asPrincipal: () -> (ret0 : Service2, ret1 : Func);
 }
diff --git a/rust/candid_parser/tests/parse_type.rs b/rust/candid_parser/tests/parse_type.rs
index 4bf218ce7..ee6351366 100644
--- a/rust/candid_parser/tests/parse_type.rs
+++ b/rust/candid_parser/tests/parse_type.rs
@@ -7,6 +7,7 @@ use candid_parser::{
 };
 use goldenfile::Mint;
 use std::io::Write;
+use std::panic::AssertUnwindSafe;
 use std::path::Path;
 
 #[test]
@@ -134,7 +135,7 @@ fn compiler_test(resource: &str) {
             {
                 match filename.file_name().unwrap().to_str().unwrap() {
                     "unicode.did" | "escape.did" => check_error(
-                        || motoko::compile(&env, &actor, &prog),
+                        AssertUnwindSafe(|| motoko::compile(&env, &actor, &prog)),
                         "not a valid Motoko id",
                     ),
                     _ => {
diff --git a/rust/candid_parser/tests/value.rs b/rust/candid_parser/tests/value.rs
index 085058f2e..80a022ccd 100644
--- a/rust/candid_parser/tests/value.rs
+++ b/rust/candid_parser/tests/value.rs
@@ -42,7 +42,16 @@ service : {
     let method = env.get_method(&actor, "f").unwrap();
     {
         let args = parse_idl_args("(42,42,42,42)").unwrap();
-        let encoded = args.to_bytes_with_types(&env, &method.args).unwrap();
+        let encoded = args
+            .to_bytes_with_types(
+                &env,
+                &method
+                    .args
+                    .iter()
+                    .map(|arg| arg.typ.clone())
+                    .collect::<Vec<_>>(),
+            )
+            .unwrap();
         let decoded = IDLArgs::from_bytes(&encoded).unwrap();
         assert_eq!(
             decoded.args,
@@ -57,10 +66,15 @@ service : {
     {
         let str = "(opt record { head = 1000; tail = opt record {head = -2000; tail = null}}, variant {a = 42})";
         let args = parse_idl_args(str).unwrap();
-        let encoded = args.to_bytes_with_types(&env, &method.rets).unwrap();
+        let rets = method
+            .rets
+            .iter()
+            .map(|ret| ret.typ.clone())
+            .collect::<Vec<_>>();
+        let encoded = args.to_bytes_with_types(&env, &rets).unwrap();
         let decoded = IDLArgs::from_bytes(&encoded).unwrap();
         assert_eq!(decoded.to_string(), "(\n  opt record {\n    1_158_359_328 = 1_000 : int16;\n    1_291_237_008 = opt record {\n      1_158_359_328 = -2_000 : int16;\n      1_291_237_008 = null;\n    };\n  },\n  variant { 97 = 42 : nat },\n)");
-        let decoded = IDLArgs::from_bytes_with_types(&encoded, &env, &method.rets).unwrap();
+        let decoded = IDLArgs::from_bytes_with_types(&encoded, &env, &rets).unwrap();
         assert_eq!(
             decoded.to_string(),
             "(\n  opt record {\n    head = 1_000 : int16;\n    tail = opt record { head = -2_000 : int16; tail = null };\n  },\n  variant { a = 42 : nat },\n)"
diff --git a/tools/didc/src/main.rs b/tools/didc/src/main.rs
index 5495319ac..76e6416d1 100644
--- a/tools/didc/src/main.rs
+++ b/tools/didc/src/main.rs
@@ -131,7 +131,7 @@ impl TypeAnnotation {
             (Some(tys), None) => {
                 let mut types = Vec::new();
                 for ty in tys.args.iter() {
-                    types.push(ast_to_type(&env, ty)?);
+                    types.push(ast_to_type(&env, &ty.typ)?);
                 }
                 Ok((env, types))
             }
@@ -139,11 +139,11 @@ impl TypeAnnotation {
                 let actor = actor
                     .ok_or_else(|| Error::msg("Cannot use --method with a non-service did file"))?;
                 let func = env.get_method(&actor, meth)?;
-                let types = match mode {
-                    Mode::Encode => &func.args,
-                    Mode::Decode => &func.rets,
-                }
-                .clone();
+                let types_iter = match mode {
+                    Mode::Encode => func.args.iter(),
+                    Mode::Decode => func.rets.iter(),
+                };
+                let types = types_iter.map(|arg| arg.typ.clone()).collect();
                 Ok((env, types))
             }
             _ => unreachable!(),