#1241: Functional dependency Coverage Condition is lifted, and should not be
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Reporter: guest | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 6.8
Component: Compiler (Type checker) | Version: 6.6
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: | Architecture: Unknown
Os: Unknown |
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Changes (by simonpj):
* milestone: _|_ => 6.8
* summary: Functional dependencies not checked. => Functional dependency
Coverage Condition is lifted, and should not be
Comment:
See also this Haskell Cafe thread
[http://www.haskell.org/pipermail/haskell-cafe/2007-March/023916.html A
question about functional dependencies and existential quantification]
The issue is identical: GHC with `-fallow-undecidable-instances` is
lifting the Coverage Condition, and probably should not do so.
Question: if we did '''not''' lift the Coverage Condition, would anyone
mind? Or perhaps lifting it deserves its own flag. Or we could combine
it with the already-scary flag `-fallow-incoherent-instances`, which also
has the same loss-of-confluence property. Opinions?
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1241>
GHC <http://www.haskell.org/ghc/>
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