#2146: Decomposition rule for equalities is too weak in case of higher-kinded
type
families
-------------------------------------+--------------------------------------
Reporter: chak | Owner: chak
Type: bug | Status: new
Priority: normal | Milestone: 6.10 branch
Component: Compiler (Type checker) | Version: 6.9
Severity: minor | Resolution:
Keywords: | Difficulty: Unknown
Testcase: | Architecture: Multiple
Os: Multiple |
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Comment (by chak):
Replying to [comment:3 claus]:
> What exactly is the intended example here?
{{{
type family F a :: * -> *
foo :: (F Int a ~ F Bool [a]) => a -> [a]
foo = undefined
}}}
Does not give rise to an error, but should, as it must be equivalent to
the following according to the ''decomposition rule'':
{{{
type family F a :: * -> *
foo :: (F Int ~ F Bool, a ~ [a]) => a -> [a]
foo = undefined
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2146#comment:5>
GHC <http://www.haskell.org/ghc/>
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