GHC/Desugar.hs

    {-# LANGUAGE Trustworthy #-}
    {-# LANGUAGE NoImplicitPrelude
               , RankNTypes
               , ExistentialQuantification
      #-}
    {-# OPTIONS_HADDOCK hide #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  GHC.Desugar
    -- Copyright   :  (c) The University of Glasgow, 2007
    -- License     :  see libraries/base/LICENSE
    --
    -- Maintainer  :  cvs-ghc@haskell.org
    -- Stability   :  internal
    -- Portability :  non-portable (GHC extensions)
    --
    -- Support code for desugaring in GHC
    --
    -----------------------------------------------------------------------------

    module GHC.Desugar ((>>>), AnnotationWrapper(..), toAnnotationWrapper) where

    import Control.Arrow    (Arrow(..))
    import Control.Category ((.))
    import Data.Data        (Data)

    -- A version of Control.Category.>>> overloaded on Arrow
    (>>>) :: forall arr. Arrow arr => forall a b c. arr a b -> arr b c -> arr a c
    -- NB: the type of this function is the "shape" that GHC expects
    --     in tcInstClassOp.  So don't put all the foralls at the front!
    --     Yes, this is a bit grotesque, but heck it works and the whole
    --     arrows stuff needs reworking anyway!
    f >>> g = g . f

    -- A wrapper data type that lets the typechecker get at the appropriate dictionaries for an annotation
    data AnnotationWrapper = forall a. (Data a) => AnnotationWrapper a

    toAnnotationWrapper :: (Data a) => a -> AnnotationWrapper
    toAnnotationWrapper what = AnnotationWrapper what