#6065: Suggested type signature causes a type error (even though it appears
correct)
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Reporter: tvynr | Owner:
Type: bug | Status: new
Priority: normal | Milestone: _|_
Component: Compiler (Type checker) | Version: 7.4.1
Keywords: type signature typeclass instance forall | Os: Linux
Architecture: x86_64 (amd64) | Failure: GHC
rejects valid program
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Comment(by simonpj):
Type variables only scope if you have an explicit `forall`. So you need
{{{
upcast :: forall ast1 ast2. (AstOp HomOp ast1 ((ast1 -> ast2) -> ast2)) =>
ast1 -> ast2
}}}
That compiles fine.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6065#comment:6>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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