#714: Inconsistency between handling functional dependencies in class and
signature constraints
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Reporter: [EMAIL PROTECTED] | Owner: simonpj
Type: bug | Status: new
Priority: low | Milestone: _|_
Component: Compiler (Type checker) | Version: 6.5
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: | Architecture: Unknown
Os: Unknown |
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Comment (by claus):
could this please be re-milestoned, for 6.10, as that seems to be the
target for completing the overhaul mentioned by Simon PJ.
since this is reported as a scope error, the same inconsistency now
applies to TFs, but there we have the additional oddity that the signature
constraint is simply dropped even if there are no type instances at all..:
{{{
class FD a b | a -> b
-- class FD a b => CFD a -- Not in scope: type variable `b'
fd :: FD a b => a
fd = undefined
type family TF a
-- class TF a ~ b => CTF a -- Not in scope: type variable `b'
tf :: TF a ~ b => a
tf = undefined
}}}
{{{
*Main> :t fd
fd :: (FD a b) => a
*Main> :t tf
tf :: a
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/714#comment:8>
GHC <http://www.haskell.org/ghc/>
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