View source for GHC/Type system

[[Category:GHC|Type system]]
<span style='font-size: x-large; font-weight: bold'>Type system extensions in GHC</span>

GHC comes with a rather large collection of type-system extensions (beyond Haskell 98).  They are all documented in the [http://www.haskell.org/ghc/docs/latest/html/users_guide/ghc-language-features.html user manual], but this page is a place to record user-oriented observations, notes, and suggestions on how to use them.

* '''[[GHC/Indexed_types|Indexed data types]]'''
* '''[[GHC/TypeHoles|Agda-like "holes" in GHC]]'''
* '''[[GHC/Stand-alone deriving declarations|"Stand-alone deriving" declarations]]'''
* '''[[GHC/TypeSigsAndAmbituity|Type signatures and ambiguity]]'''
* '''Overlapping instances'''.  GHC supports overlapping instances, with carefully specified rules. Make sure you read the [http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#instance-decls relevant sections of the user manual].  Here is an appliation note about [[GHC/AdvancedOverlap|advanced use of overlapping instances]], combined with functional dependencies.