Compiling Scheme to WebAssembly

4 months ago

Bob, a suite of Scheme implementations in Python, celebrated its 15th anniversary.
Originally, Bob included an interpreter, compiler, and VM to explore CPython-like bytecode VMs.
A C++ VM was later added to experiment with low-level VM implementation without Python's runtime support, featuring a custom mark-and-sweep GC.
Recently, a new compiler was added to translate Scheme directly to WebAssembly (WASM).
Goals included experimenting with lowering high-level languages to WASM and gaining hands-on experience with the WASM GC extension.
Key Scheme objects like PAIR, BOOL, and SYMBOL were represented in WASM GC, utilizing features like i31 for unboxed integers.
Symbols are stored in linear memory with offsets and lengths, enabling string interning.
The 'write' builtin was implemented directly in WASM text, importing minimal host functions for character and integer output.
The project provided valuable insights into realistic WASM code emission and Scheme's implementation challenges.

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