#3851: type family does not get expanded in ghc-6.12.1
---------------------------------+------------------------------------------
Reporter: kosmikus | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (Type checker)
Version: 6.12.1 | Keywords:
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: GHC rejects valid program
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The following code (which is a trimmed down version of an application of
the multirec library) does not compile on ghc-6.12.1,
but it does with ghc-6.10.4. Why?
{{{
{-# LANGUAGE GADTs, TypeFamilies #-}
type family TF a :: * -> *
type instance TF () = App (Equ ())
data Equ ix ix' where Refl :: Equ ix ix
data App f x = App (f x)
-- does not typecheck in 6.12.1 (but works in 6.10.4)
bar :: TF () () -> ()
bar (App Refl) = ()
-- does typecheck in 6.12.1 and 6.10.4
ar :: App (Equ ()) () -> ()
ar (App Refl) = ()
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3851>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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