v0.1.0

The first release. The compiler pipeline works end to end: the flagship
demo — a supervised agent planner — type-checks, compiles to readable
Erlang, and runs on BEAM.

What v0.1 does

• Effect rows, checked for equality. A function's declared row
  (! {Tool<CreateTicket>, Tool<Log>}) must equal exactly what its body
  performs — not a superset, not a subset. Effect polymorphism is
  expressed with row variables, never by subsumption.
• Tool effects, audited unconditionally. tool Name : {args} → result
  declares the only I/O boundary, yielding an effect, a callable
  function, and a derived invocation record. Every call is recorded on
  an audit stream as one canonical JSON line — mocked and real handlers
  audit identically, so dry runs and production leave the same trail.
• Typed actors on OTP. An actor is a typed gen_server: a state
  type, a message sum type, and one handler per constructor, with
  exhaustiveness checked and a per-handler effect row. Supervisors
  declare their strategy, restart budget, and typed children.
• Queryable by tooling, not just readable. Effect rows are
  per-process by design, so "what does this actor do transitively" is a
  tooling query rather than a type-system feature:
  hird emit-effect-graph and the MCP server answer it from the IR.
• LSP and MCP servers over the same compiler front end — diagnostics,
  hover, and go-to-definition for editors; eight introspection tools for
  LLM agents.

Known limits

The language surface is unstable and will break without deprecation
cycles. The LSP and MCP servers compile one file at a time, so use
imports do not resolve in editor and agent queries (the CLI checks a
whole directory as one program). There is no incremental compilation.
The backend emits Erlang source rather than abstract forms, and
request blocks on a fixed 5000 ms timeout. The
roadmap is
tracked in-repo.

Install

Download the archive for your platform below and extract it; each one
carries three binaries:

• hird — the compiler CLI (check, build, run, emit-ast, emit-effect-graph)
• hird-lsp — the language server (diagnostics, hover, go-to-definition)
• hird-mcp — the MCP server exposing compiler introspection to LLM agents

Or build from source with Rust 1.97+:

cargo install --git https://github.com/no-materials/hird hird-cli

Compiling and running Hirð programs (hird build, hird run) needs
Erlang/OTP on PATH; hird check works without it.

See the README to get started.