#7352: this type signature in a case alternative does not typecheck and requires
ScopedTypeVariables
---------------------------------+------------------------------------------
Reporter: atnnn | Owner: atnnn
Type: bug | Status: closed
Priority: normal | Component: Compiler (Type checker)
Version: 7.6.1 | Resolution: invalid
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Testcase: | Blockedby:
Blocking: | Related:
---------------------------------+------------------------------------------
Changes (by atnnn):
* status: new => closed
* resolution: => invalid
Comment:
This is not a bug, just the normal behaviour of GADTs
{{{
{-# LANGUAGE GADTs #-}
data G a where
G :: {unG :: a} -> G [a]
test4 (G True) = ()
}}}
test4 fails with
{{{
Could not deduce (a ~ Bool)
from the context (t ~ [a])
}}}
Here is a workaround that works
{{{
test5 g | True <- unG g = ()
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7352#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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