#2664: type family + data family + typeclass + type error causes GHC to diverge
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Reporter: ryani | Owner: chak
Type: bug | Status: new
Priority: normal | Milestone: 6.12 branch
Component: Compiler | Version: 6.11
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: | Os: Unknown/Multiple
Architecture: Unknown/Multiple |
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Comment (by chak):
Replying to [comment:6 simonpj]:
> HEAD gives
{{{
WARNING: file compiler/types/Coercion.lhs line 465
Strange! Type mismatch in trans coercion, probably a bug
...plus some more...
}}}
> But Manuel thinks the WARNING has false positives. (Maybe we should nuke
it.)
One case of false positives is when one of the compared types contains an
unzonked type variable. I believe this situation arises during solving
quality constraints. In most other places where trans coercions are made,
the test may be accurate. So, if we knew the caller, it would be easier
to say whether a particular warning may potentially be a false positive.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2664#comment:7>
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