#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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Comment (by simonpj):
Ah, but if you want the Weak Coverage Condition then the functional
dependencies must be "full" (see the paper). So we seem agreed that
* `-fallow-undecidable-instances` should not lift the Coverage Condition.
Beyond that we could also:
* Replace the Coverage Condition by the Weak Coverage Condition
(suitably modified to account for "fullness"). I think the modification
is: either the Coverage Condition is satisified, or the FDs of this class
are full and the Weak Coverage Condition is satisfied.
And perhaps also
* Allow whatever coverage condition we have to be lifted
* Either by `-fallow-incoherent-instances`
* Or by a new flag `-fno-coverage-condition`
None of this sounds too hard, but I can't say I'm eager to get on with it
:-)
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1241>
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