#6032: HEAD (7.5.20120421) requires RankNTypes for a rank-2 type
------------------------------+---------------------------------------------
Reporter: dreixel | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.5 | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: None/Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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While building syb with HEAD, Ian reported that he needed to use
RankNTypes instead of Rank2Types. I minimized the problem to:
{{{
{-# LANGUAGE Rank2Types #-}
module Rank2 where
f :: (forall a. a -> (forall b. b)) -> c
f = undefined
g :: (forall a b. a -> b) -> c
g = undefined
}}}
7.4 accepts both `f` and `g`. HEAD complains on the signature of `f`:
{{{
Illegal polymorphic or qualified type: forall b. b
Perhaps you intended to use -XRankNTypes or -XRank2Types
In the type signature for `f':
f :: (forall a. a -> (forall b. b)) -> c
}}}
It doesn't complain about `g`, but I think the signatures are equivalent.
Ian further reports that the change in behavior seems to have occurred
after 7.5.20120401.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6032>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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