haskell-coder

Run cabal init to generate a .cabal file defining library, executable, and test-suite stanzas with build-depends and default-language Haskell2010. Use a common stanza to share warning flags like -Wall and -Wcompat across components, and follow the PVP for dependency version bounds.

Enable only DeriveGeneric, DerivingStrategies, LambdaCase, and ScopedTypeVariables via default-extensions in the cabal file. Enable everything else, such as OverloadedStrings or TemplateHaskell, with per-file LANGUAGE pragmas to keep effects localized and auditable.

Use Text from the text package for all string data; String is a linked list of Char and performs poorly. Enable OverloadedStrings per-file for Text literals, and use ByteString for binary data.

Use the strict left fold foldl' instead of lazy foldl, add bang patterns to accumulator bindings, and mark record fields strict with bangs. Profile with cabal build --enable-profiling and run with +RTS -hc to inspect heap usage.

Prefer a single ReaderT Env IO newtype over deep stacks like ExceptT over StateT over ReaderT. Store mutable state in IORef or TVar fields inside the environment, throw exceptions in IO, and use Has-typeclass constraints for granular access.

Yes, use haskell-flake or nixpkgs haskellPackages shellFor to get reproducible builds with pinned GHC versions and tools like haskell-language-server and ghcid. Overrides let you pin Hackage versions, apply jailbreaks, or add C library dependencies.