Source code:

Bil

Bil is an extension to Go that adds language and runtime support for parallel processors, see docs/guide.md for an introduction to the Bil language, expressed as worked examples.

Install

Bil needs a Go toolchain on PATH at runtime - get Go from https://go.dev/dl/ if you don’t already have it.

On macOS, Linux, etc.:

curl -fsSL https://bil-lang.org/install.sh | sh

On Windows (PowerShell):

irm https://bil-lang.org/install.ps1 | iex

These install a prebuilt bil binary for your platform, and place it on your PATH.

Run Bil code

Run a .bil file with:

bil run examples/01-twoprocs.bil

bil run chains together Bil’s two internal tools:

  1. tools/bilc — a source-to-source preprocessor (a transpiler) that uses go/scanner and go/token to parse Bil code, apply certain heuristic rules and to provide a set of helper functions. Finally, it uses go/format to translate the .bil file into legal Go.
  2. tools/vet — a go/ast/go/types-based static analyzer that checks the transpiled Go against Bil’s usage rules (for example: a channel may only be used for input in one par branch, and output in one other).
  3. Only if that passes: calls go run on the transpiled Go.

To run steps 1–2 only, without executing the program, use bil vet instead of bil run.

Editor support

There’s no dedicated .bil grammar yet, but since Bil is close enough to Go syntactically, telling your editor to highlight .bil files as Go gets you most of the way there. In VSCode, add this to settings.json (workspace or user): "files.associations": { "*.bil": "go" }. This just picks the highlighter — it doesn’t run gofmt/gopls against .bil files, since they aren’t valid Go until bilc rewrites them. Other editors / IDEs will have similar settings.

Run tests

cd tools/bilc
go test ./...

This runs tools/bilc/bilc_test.go against the fixtures in tools/bilc/testdata/: ok/*.bil files are transpiled, run, and checked against a matching *.golden file; err/*.bil files are checked to fail with an error containing the matching *.err file’s text. To add a regression test, drop a new .bil + .golden (or .err) pair into the right directory — no test code to touch.

ok/*.bil fixtures need deterministic output, since they’re checked with an exact string match. An example whose output is inherently timing-dependent (e.g. examples/03-server-alt.bil, which races a timer against a sleep) is deliberately left out of testdata/, and is only meant to be run manually via bil run.

tools/vet and tools/bil have their own go test ./... suites, run the same way from within each directory.

Build from source

To build it from source instead:

cd tools/bil && go build -o bil . && cd ../..

(the examples assume bil is on PATH; if you built from source without moving the binary, run tools/bil/bil in its place)

License

Copyright (c) 2026 Stephen Roe. BSD 3-Clause license – see LICENSE. See NOTICE for the occam/CSP and Go influences and attributions (Go’s own license text is in LICENSE-GO).