#5377: TypeSynonymInstances dysfunctional in ghc-7.2.1-rc1?
-------------------------------+--------------------------------------------
Reporter: hvr | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.1 | Keywords:
Testcase: | Blockedby:
Os: Linux | Blocking:
Architecture: x86_64 (amd64) | Failure: GHC rejects valid program
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The following code causes GHC to suggest enabling the TypeSynonymInstances
language extension:
{{{
#!hs
type Foo = Maybe Int
class Bar x where
bar :: x -> ()
bar _ = ()
instance Bar Int
instance Bar Foo
}}}
but adding a `{-# LANGUAGE TypeSynonymInstances #-}` doesn't suffice, as
GHC then suggests enabling FlexibleInstances instead.
With ghc-7.0.4 the TypeSynonymInstances extension by itself was enough to
make the code above compile. This breaks compilation for a few packages on
hackage which assume that TypeSynonymInstances suffices.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5377>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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