A simplified view on the haskell-src-exts AST


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MIT licensed by Bertram Felgenhauer
Maintained by Bertram Felgenhauer
This version can be pinned in stack with:haskell-src-exts-simple-,1519
Used by 1 package in lts-12.14(full list with versions):



This package provides a shim for haskell-src-exts, exposing the same AST but without annotations, using ghc’s pattern synonyms.

This package is useful for synthesizing and manipulating HSE ASTs that don’t carry source location information. It may also aid in porting packages from haskell-src-exts 1.17 to 1.18, but it is not a drop-in replacement for the old annotation-free AST. See the Compatibility section for details.


To be able to track the haskell-src-exts version numbers conveniently, the first three components of the version will be treated as the major version, followed by the minor version as usual. This deviates from the PVP.


Comparison to haskell-src-exts 1.17 (as of version 1.18):

haskell-src-exts-simple provides a simplified view of the annotated AST in haskell-src-exts, so there are differences to the unannotated AST provided by earlier versions of haskell-src-exts:

  • some constructors carried SrcLoc information, which is no longer available, notably
    • most constructors of the Decl, ModulePragma, ImportDecl, IPBind, ClassDecl, InstDecl, QualConDecl, GadtDecl datatypes
    • the Lambda, ExpTypeSig and Proc constructors of the Exp type (and a few XML related ones)
    • the Generator constructor of Stmt
    • the Alt constructor of Alt
    • the PatTypeSig constructor of Pat
  • the second, fourth and fifth fields of the Module constructor have been combined into a single field of type ModuleHead

(this list is probably incomplete)

ghc compatibility

  • haskell-src-exts-simple requires ghc-7.8 or later
  • Note that with ghc-7.8, the constructors of the Language.Haskell.Exts.Simple.Syntax.Literal type are only available for pattern matching, because construction relies on explicitly bidirectional pattern synonyms for literals. For ghc-7.8 compatibility, you should use the *L (intL etc.) functions for constructing Literal values.
  • Support for record pattern synonyms was added in ghc-8.0. Therefore, with ghc-7.10 and earlier, the constructor of the Language.Haskell.Exts.Simple.Syntax.ImportDecl type is exported as a plain constructor, and the selectors as functions.


Revision history for haskell-src-exts-simple – 2017-12-??

  • support haskell-src-exts 1.20.0 – 2016-11-20

  • support haskell-src-exts 1.19.0
  • implement Language.Haskell.Exts.Simple.Syntax.ImportDecl as a record pattern synonym for ghc-8.0 – 2016-08-05

  • package description should now look fine on hackage – 2016-08-02

  • ghc-7.8 compatibility (see COMPATIBILITY.md for caveats)

1.18.0 – 2016-07-31

  • Initial release.