Haskell Source Extensions

haskell-src-exts is a package for handling and manipulating Haskell source code. It is a descendant of the haskell-src package that is part of the standard libraries, but extends this to support a number of syntactic extensions, e.g. MPTCs, fundeps, GADTs, TH etc. The aim is to support all extensions recognized by the community, as determined by what is implemented in compilers and tools.

Apart from the more standard extensions supported by e.g. GHC, haskell-src-exts provides support for HaRP (Haskell Regular Patterns) and HSX (Haskell Source with XML) syntax.

Package structure

The modules that comprise haskell-src-exts all reside in the hierarchic namespace Language.Haskell.Exts, or its more feature-rich sibling Language.Haskell.Exts.Annotated. Notable exposed modules include:

  • Language.Haskell.Exts[.Annotated] - Imports and re-exports all the below, and also defines some functions that combine functionality from several modules.
  • Language.Haskell.Exts[.Annotated].Syntax - The abstract syntax tree that the other modules work on.
  • Language.Haskell.Exts[.Annotated].Build - Combinators for building abstract syntax.
  • Language.Haskell.Exts[.Annotated].Parser - Functions for parsing Haskell source code into an abstract syntax representation.

Non-comprehensive list of supported extensions

  • Multi-parameter type classes (MPTCs)
  • Functional dependencies
  • Associated types, type families
  • Liberal class and instance heads
  • Implicit parameters (ghc and hugs)
  • Explicit kind signatures
  • Pattern guards
  • Generalized algebraic data types (GADTs)
  • Template Haskell (TH)
  • Universal and existential quantification (forall)
  • Empty data type declarations
  • Unboxed tuples (# #)
  • Standalone deriving
  • Regular patterns
  • Haskell XML, HSX style
  • Pragmas


The haskell-src-exts Package is distributed under a derived BSD-style license. It derives from several sources, all of which are distributable under BSD-style or compatible licenses. See the file LICENSE for the complete license text.