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tree-sitter-haskell

Test the grammar

Haskell grammar for tree-sitter.

Note This grammar needs at least tree-sitter 0.19.4 and C++-14.

References

Building with nvim-treesitter

When installing the grammar from source, be sure to include the scanner in the source files:

lua <<EOF
local parser_config = require "nvim-treesitter.parsers".get_parser_configs()
parser_config.haskell = {
  install_info = {
    url = "~/path/to/tree-sitter-haskell",
    files = {"src/parser.c", "src/scanner.cc"}
  }
}
EOF

Depending on what compilers are installed in your system, it may be necessary to force nvim-treesitter to use a specific one to satisfy the C++-14 requirement (see this issue for more info):

lua require'nvim-treesitter.install'.compilers = { "clang" }
" or
lua require'nvim-treesitter.install'.compilers = { "clang++" }

or

lua require'nvim-treesitter.install'.compilers = { "gcc" }

Building on MacOS

If you get loads of C++ errors when building the parser, a workaround might be to install GCC with homebrew, in addition to selecting gcc as the compiler used by tree-sitter, as described for Neovim in the previous section.

First, run this command in a terminal:

$ brew install gcc

This may not be enough, since clang might still be used by default. You can find out whether the gcc executable is linked to something else with:

$ ls -l $(which gcc)

If this doesn't point to something like gcc-11, you can remove it (if it is a symlink) and/or link the real gcc-N binary to a bin directory that's at the head of your $PATH, something like:

ln -sf /opt/homebrew/bin/gcc-11 /usr/local/bin/gcc

or this for earlier versions of homebrew.

ln -sf /usr/local/bin/gcc-11 /usr/local/bin/gcc

Supported Language Extensions

These extensions are supported ✅, unsupported ❌ or not applicable because they don't involve parsing ➖️:

  • AllowAmbiguousTypes ➖️
  • ApplicativeDo ➖️
  • Arrows ❌
  • BangPatterns ✅
  • BinaryLiterals ✅
  • BlockArguments ✅
  • CApiFFI ✅
  • ConstrainedClassMethods ✅
  • ConstraintKinds ✅
  • CPP ✅
  • CUSKs ✅
  • DataKinds ✅
  • DatatypeContexts ✅
  • DefaultSignatures ✅
  • DeriveAnyClass ➖️
  • DeriveDataTypeable ➖️
  • DeriveFoldable ➖️
  • DeriveFunctor ➖️
  • DeriveGeneric ➖️
  • DeriveLift ➖️
  • DeriveTraversable ➖️
  • DerivingStrategies ✅
  • DerivingVia ✅
  • DisambiguateRecordFields ➖️
  • DuplicateRecordFields ➖️
  • EmptyCase ✅
  • EmptyDataDecls ✅
  • EmptyDataDeriving ✅
  • ExistentialQuantification ✅
  • ExplicitForAll ✅
  • ExplicitNamespaces ✅
  • ExtendedDefaultRules ➖️
  • FlexibleContexts ✅
  • FlexibleInstances ✅
  • ForeignFunctionInterface ✅
  • FunctionalDependencies ✅
  • GADTs ✅
  • GADTSyntax ✅
  • GeneralisedNewtypeDeriving ➖️
  • GHCForeignImportPrim ✅
  • Haskell2010 ➖️
  • Haskell98 ➖️
  • HexFloatLiterals ✅
  • ImplicitParams ✅
  • ImplicitPrelude ➖️
  • ImportQualifiedPost ✅
  • ImpredicativeTypes ➖️
  • IncoherentInstances ➖️
  • InstanceSigs ✅
  • InterruptibleFFI ✅
  • KindSignatures ✅
  • LambdaCase ✅
  • LexicalNegation ❌
  • LiberalTypeSynonyms ✅
  • LinearTypes ✅
  • MagicHash ✅
  • Modifiers ❌
  • MonadComprehensions ➖️
  • MonadFailDesugaring ➖️
  • MonoLocalBinds ➖️
  • MonomorphismRestriction ➖️
  • MultiParamTypeClasses ✅
  • MultiWayIf ✅
  • NamedFieldPuns ✅
  • NamedWildCards ✅
  • NegativeLiterals ➖️
  • NondecreasingIndentation ❌
  • NPlusKPatterns ➖️
  • NullaryTypeClasses ✅
  • NumDecimals ➖️
  • NumericUnderscores ✅
  • OverlappingInstances ➖️
  • OverloadedLabels ✅
  • OverloadedLists ➖️
  • OverloadedStrings ➖️
  • PackageImports ✅
  • ParallelListComp ✅
  • PartialTypeSignatures ✅
  • PatternGuards ✅
  • PatternSynonyms ✅
  • PolyKinds ➖️
  • PostfixOperators ➖️
  • QualifiedDo ✅
  • QuantifiedConstraints ✅
  • QuasiQuotes ✅
  • Rank2Types ✅
  • RankNTypes ✅
  • RebindableSyntax ➖️
  • RecordWildCards ➖️
  • RecursiveDo ✅
  • RoleAnnotations ✅
  • Safe ➖️
  • ScopedTypeVariables ✅
  • StandaloneDeriving ✅
  • StandaloneKindSignatures ✅
  • StarIsType ✅
  • StaticPointers ❌
  • Strict ➖️
  • StrictData ➖️
  • TemplateHaskell ✅
  • TemplateHaskellQuotes ✅
  • TraditionalRecordSyntax ➖️
  • TransformListComp ✅
  • Trustworthy ➖️
  • TupleSections ✅
  • TypeApplications ✅
  • TypeFamilies ✅
  • TypeFamilyDependencies ✅
  • TypeInType ✅
  • TypeOperators ✅
  • TypeSynonymInstances ➖️
  • UnboxedSums ✅
  • UnboxedTuples ✅
  • UndecidableInstances ➖️
  • UndecidableSuperClasses ➖️
  • UnicodeSyntax ✅
  • UnliftedFFITypes ➖️
  • UnliftedNewtypes ✅
  • Unsafe ➖️
  • ViewPatterns ✅

Bugs

CPP

Preprocessor #elif and #else directives cannot be handled correctly, since the parser state would have to be manually reset to what it was at the #if. As a workaround, the code blocks in the alternative branches are parsed as part of the directives.

Layout

NondecreasingIndentation is not supported (yet?).

Operators on newlines in do

A strange edge case is when an infix operator follows an expression statement of a do block with an indent of less or equal the do's layout column:

f = do
  readSomething
  >>= doSomething

The >>= causes the do's layout to be terminated, resulting in an AST similar to

f = (do readSomething) >>= doSomething

This is checked heuristically, probably unreliably.