[GHC] #7785: Module-local function not specialized with ConstraintKinds

[GHC]

#7785: Module-local function not specialized with ConstraintKinds
------------------------------------+---------------------------------------
Reporter:  akio                     |          Owner:                  
    Type:  bug                      |         Status:  new             
Priority:  normal                   |      Component:  Compiler        
 Version:  7.6.2                    |       Keywords:  specialisation  
      Os:  Unknown/Multiple         |   Architecture:  Unknown/Multiple
 Failure:  Runtime performance bug  |      Blockedby:                  
Blocking:                           |        Related:                  
------------------------------------+---------------------------------------

Comment(by akio):

 This can be worked around by defining a wrapper class such that the
 constraint kind no longer directly shows up in the type signatures.

 {{{
 --- spec.hs     2013-03-22 15:41:23.000000000 +0900
 +++ spec2.hs    2013-03-22 15:38:30.000000000 +0900
 @@ -1,10 +1,12 @@
 -{-# LANGUAGE TypeFamilies, ConstraintKinds #-}
 +{-# LANGUAGE TypeFamilies, ConstraintKinds, MultiParamTypeClasses,
 UndecidableInstances, FlexibleContexts, FlexibleInstances #-}

  module Foo(foo, bar, foo', bar') where

  import GHC.Exts

  type family Domain (f :: * -> *) a :: Constraint
 +class Domain f a => Domain' (f :: * -> *) a
 +instance Domain f a => Domain' f a

  type instance Domain [] a = ()

 @@ -12,9 +14,9 @@
    myfmap = map

  class MyFunctor f where
 -  myfmap :: (Domain f a, Domain f b) => (a -> b) -> f a -> f b
 +  myfmap :: (Domain' f a, Domain' f b) => (a -> b) -> f a -> f b

 -shared :: (MyFunctor f, Domain f Int) => f Int -> f Int
 +shared :: (MyFunctor f, Domain' f Int) => f Int -> f Int
  shared = let
    f = myfmap negate
    in
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7785#comment:1>
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