Declarative WASM GC Types

This page is a technical blog post by MonoidMusician that examines how to model WebAssembly GC types in a declarative style. It starts from the observation that WASM modules are designed for linear parsing and validation, with complex types listed up front and referenced by index, which becomes awkward once nested structured types and recursive type groups enter the picture.

The core of the article introduces a layered type vocabulary: stack types (WTyp), function types, heap types (HTyp), heap type classifiers (HCls), composite types (CTyp), recursive types (RTyp), and subtypes (SubTyp). These abstractions aim to make the relationships between WASM GC types explicit and easier to reason about when generating modules.

The post is aimed at developers building WASM toolchains, compilers, or validators, and at anyone who has struggled with the WASM specification’s organization and formatting. It assumes familiarity with WebAssembly and its GC extension.

Readers should treat it as a design discussion rather than a tutorial, and may benefit from consulting the official WASM spec alongside it. Overall, it offers a useful conceptual framework for handling recursive and composite types declaratively.