BHC v0.2.2

BHC v0.2.2

The first release of 2026 with material progress against
real-world Haskell. v0.2.2 is a stability-and-coverage release —
the headline numbers move, the REPL becomes booth-usable, and the
release tarball finally ships the standard library it needs to
link a hello-world.

Highlights

• Pandoc — bhc check: 78 / 221 modules pass (up from
  4 / 221 at v0.2.1).
  The parser sees all 221 modules; 91 still fail in lowering or
  type-checking and 52 are skipped pending external-package support.
  Live numbers on the status page.
• zentinel-agent-policy — 10 / 10 modules compile. The full
  Zentinel.Agent.Policy.* graph goes through the multi-module
  pipeline and emits object code. See
  the milestone post.
• bhci REPL is now usable. Pure-expression evaluation, recursive
  let, persistent bindings, list comprehensions, polymorphic
  arithmetic, accurate type display. See the
  REPL section in the demos folder.
• Install path repaired. v0.2.1 tarballs shipped without the
  standard library, so curl install.sh | sh left users one
  hello-world away from a link error. Fixed.

What got better

Language coverage

• Multi-module pipeline with cross-module type propagation, circular
  imports, qualified-name resolution, re-export handling, and ~120
  builtin module stubs (Data.Text, transformers, ByteString, Map, Set,
  Sequence, Djot, Skylighting, DocLayout, and more).
• Existential types end-to-end (parser → typechecker → codegen with
  dictionary dispatch).
• Multi-argument class methods, RankNTypes, multi-line export
  lists, alias-qualified imports.
• Layout rule edge cases: VirtualRBrace before in, qualified
  constructors at the start of pattern bindings, multi-line Haddock
  collection.
• Parser correctness fixes: backtick infix precedence, !/?/#
  as binary operators, Haddock comments before module, tuple
  constructors up to 15-tuples, char literal lexing, nested where
  clauses, parameterised CPP/diagnostics in the loader.

Evaluator

• /= was an alias for == and returned wrong results everywhere it
  appeared in source. Now properly negates equality.
• +, -, *, negate were hardcoded to integer arithmetic; calling
  them on Float or Double either errored or silently returned 0.
  Now polymorphic across Int, Integer, Float, Double.
• REPL let dispatch no longer misroutes let f n = ... in f 5 as a
  binding declaration.
• Type display in bhci no longer prints t586 for unresolved
  schemes; falls back to the runtime value shape and recurses into
  lists, tuples, Maybe, and Either.

Packaging

• Release tarball now contains all nine stdlib static libraries
  (libbhc_text.a, libbhc_base.a, libbhc_prelude.a, ...) in
  addition to libbhc_rts.a. Sizes up from ~39 MB to ~96 MB
  compressed; the alternative was broken installs.
• Workflow fails loudly if any of the four critical archives (rts,
  text, base, prelude) is missing.

Compatibility

This release stays within the documented Haskell baseline. The
compatibility charter covers
the GHC2021 / GHC2024 subset BHC currently supports. Template Haskell
remains out of scope.

Known issues

A few rough edges are documented honestly rather than hidden:

• let t = expr; describe t inside a do block routes user class
  methods through an RTS stub instead of dispatching on the
  user-supplied instance. Workaround: invoke the class method on the
  value directly, or via a top-level binding. Will be fixed in the
  next release.
• Recursive where-bound helpers with guards can segfault under
  native compilation in some shapes. Workaround: hoist the helper to a
  top-level function.
• WebAssembly binaries validate against wasmtime but the Core IR
  → WASM lowering for general programs is incomplete. WASM E2E tests
  are 0 / 6.
• GPU backends pass mock-mode tests (2 / 2 PTX) but require CUDA
  hardware for real end-to-end testing.

Installation

# Recommended (Linux / macOS):
curl -fsSL https://arcanist.sh/bhc/install.sh | sh

# Or via Homebrew:
brew install arcanist-sh/tap/bhc

# Then:
echo 'main = putStrLn "Hello!"' > hello.hs
bhc hello.hs -o hello
./hello

Platforms

This release includes binaries for:

• Linux x86_64
• macOS aarch64 (Apple Silicon)

Linux aarch64, macOS x86_64 (Intel), and Windows are not yet packaged.

Checksums

See SHA256SUMS.txt for file checksums.

Coming up

The next release will focus on type-checking failures in modules that
currently cross lowering but stall on partial stub typing, and on the
two native-codegen bugs noted above. Pandoc compatibility numbers will
keep moving as those land.