formawasm

formawasm compiles a formalang Intermediate Representation (IR) module into a WebAssembly component — a .wasm binary that any standards-compliant runtime can execute.

formalang frontend ──► IrModule ──► formawasm ──► .wasm component ──► host runtime

formawasm is a backend: it doesn't parse .fv source files itself, and it doesn't run the resulting wasm. Both jobs belong to other libraries (formalang for parsing, wasmtime / wasmi / a browser engine for execution). formawasm only emits bytes.

The boundary between a component and its host is described in WIT — the small Interface Definition Language of the Component Model. formawasm generates the WIT file automatically from the public surface of each IR module; the host never hand-writes WIT.

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Quickstart

Install the CLI:

cargo install formawasm

Or pin to a specific version:

cargo install formawasm --version 0.0.1-beta

Compile a .fv source file:

echo 'pub fn id(x: I32) -> I32 { x }' > id.fv
formawasm id.fv
# wrote id.wasm (… bytes) from id.fv

Inspect the generated WIT interface:

wasm-tools component wit id.wasm

package formawasm:generated;

world component {
  export id: func(x: s32) -> s32;
}

Run it directly with the wasmtime CLI — no host code required:

wasmtime run --invoke 'id(42)' id.wasm
# 42

Or wire it into your Rust application:

use wasmtime::{Config, Engine, Store};
use wasmtime::component::{Component, Linker};

let mut config = Config::new();
config.wasm_component_model(true);
let engine = Engine::new(&config)?;

let bytes = std::fs::read("id.wasm")?;
let component = Component::from_binary(&engine, &bytes)?;
let linker = Linker::<()>::new(&engine);
let mut store = Store::new(&engine, ());
let instance = linker.instantiate(&mut store, &component)?;

let id = instance.get_typed_func::<(i32,), (i32,)>(&mut store, "id")?;
let (got,) = id.call(&mut store, (42,))?;
assert_eq!(got, 42);

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Documentation

The full book lives at docs/ and is built with mdBook:

mdbook serve            # local dev server with live reload

Highlights:

For users (embedding formawasm in a Rust application):

• Quickstart — .fv → .wasm in 30 seconds
• Using the Library — WasmBackend from your own crate
• Hosting a Component — running components under wasmtime
• Boundary Policy — what can cross the WIT boundary
• Type Mapping — formalang ↔ WIT
• Feature Coverage — what's supported, per IR variant
• Cargo Features — wasm-opt, dwarf, validation
• Troubleshooting — common errors

For contributors (extending the backend):

• Architecture — the seven-stage pipeline
• Crate Layout — what's in src/
• Lowering — memory model, runtime helpers, per-IrExpr lowering
• Extending the Backend — adding IR variants, runtime helpers, layouts
• Testing — test conventions and milestone tests
• Contributing — code style, quality gates, microcommit cadence

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Status

Phases 1 through 5 are closed. The backend produces a Component-Model artifact for every milestone — recursive functions (fib), structs + enums + methods (Counter / Action), arrays + ranges + for-loops (sieve of Eratosthenes), strings + optionals + dictionaries (greet), virtual dispatch (Greet trait across two impls), and host-provided externs (call_host(21) → 42 via host_double).

See CHANGELOG.md for the phase-by-phase history; the "Roadmap" section at the top captures what's left.

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License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.