#6100: mistake in class inheritance system
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Reporter: guest | Owner:
Type: bug | Status: closed
Priority: normal | Component: Compiler
Version: 7.4.1 | Resolution: invalid
Keywords: class inheritance | Os: Linux
Architecture: x86 | Failure: GHC rejects valid program
Testcase: | Blockedby:
Blocking: | Related:
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Changes (by kosmikus):
* status: new => closed
* resolution: => invalid
Comment:
No, GHC is correct.
{{{
func :: A a => a -> a -> Int
}}}
Note that both arguments have to have the *same* type. You have
{{{
f :: (A a, B b) => a -> b -> Int
}}}
While both arguments must be members of `A`, they don't have to be of the
same concrete type. And that's exactly the error message you get, namely
that GHC cannot deduce that `a` is equal to `b` (where `~` is GHC's way to
denote type-level equality).
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6100#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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