pure-borrow: Skill for Codex

Haskell Development Super-Skill

This is the entry point for Haskell development in this repository. It coordinates the Codex skills with the agent-agnostic repository policy in AGENTS.md:

• Hoogle lookup maps to .codex/skills/hoogle.
• Haddock dependency documentation lookup maps to .codex/skills/haddock.
• Formatting maps to .codex/skills/haskell-format, .codex/skills/haskell-cabal-gild, and the shared hooks under .agents/hooks/.
• Prefer HLS when available before falling back to full Cabal builds.

Ground Rules

• Use cabal nix-style builds. cabal.project and cabal.project.local are the source of truth.
• Do not use stack or invoke ghc directly for normal validation.
• In a multi-package project, work on and build one package at a time with cabal build <pkg>. Get it green before moving to another package.
• Format changed .hs, .lhs, and .hsig files with the haskell-format skill before compiling.
• Format changed .cabal, cabal.project, cabal.project.local, and cabal.project.freeze files with the haskell-cabal-gild skill before compiling.
• Prefer (<>) over (++) for all concatenation, including lists and strings.
• Quantify lifetime type parameters as α, β, γ, with primes or numeric suffixes as needed; do not use prose lifetime names such as lifetime, scope, or inner.
• Never call unsafePerformIO (or unsafeDupablePerformIO, unsafeThaw, unsafeIOToST) in a direct… benchmark baseline. Write the plain-vector baseline with modify, which takes a forall s. MVector s a -> ST s () and handles thaw/freeze itself; use STRef for auxiliary mutable state. See the benchmark section of AGENTS.md.
• After changing any Haskell source, run cabal build all and then cabal test before committing. The plain build must come first: the doctest suite reads the built library. Keep -O2 (pinned in cabal.project); the inspection suite asserts optimized-Core properties that hold vacuously at -O1.
• There is no package.yaml/hpack in this repository; edit .cabal files directly.