{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE NoImplicitPrelude
           , RankNTypes
           , ExistentialQuantification
  #-}
{-# OPTIONS_HADDOCK not-home #-}

-----------------------------------------------------------------------------
-- |
-- 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 :: arr a b
f >>> :: forall a b c. arr a b -> arr b c -> arr a c
>>> g :: arr b c
g = arr b c
g arr b c -> arr a b -> arr a c
forall k (cat :: k -> k -> *) (b :: k) (c :: k) (a :: k).
Category cat =>
cat b c -> cat a b -> cat a c
. arr a b
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 :: a -> AnnotationWrapper
toAnnotationWrapper what :: a
what = a -> AnnotationWrapper
forall a. Data a => a -> AnnotationWrapper
AnnotationWrapper a
what