#3169: Type families occurs check
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Reporter: simonpj | Owner: chak
Type: bug | Status: closed
Priority: normal | Milestone: 6.12.1
Component: Compiler | Version: 6.10.2
Severity: normal | Resolution: worksforme
Keywords: | Difficulty: Unknown
Testcase: | Os: Unknown/Multiple
Architecture: Unknown/Multiple |
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Changes (by chak):
* status: new => closed
* resolution: => worksforme
Comment:
I disagree. GHC is perfectly right. You forgot to match the ''data
constructor'' `MP` in the second argument of `lookup`.
{{{
instance (Key a, Key b) => Key (a,b) where
type Map (a,b) = MP a b
lookup (a,b) (MP m)
= case lookup a m of
Just m2 -> lookup b m2
}}}
works fine for me in the HEAD.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3169#comment:1>
GHC <http://www.haskell.org/ghc/>
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