#1723: type unsafety with type family + GADT
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Reporter: [EMAIL PROTECTED] | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler (Type checker) | Version: 6.8
Severity: major | Resolution:
Keywords: | Difficulty: Unknown
Os: Unknown | Testcase:
Architecture: Unknown |
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Comment (by toms):
The current work-around is to write:
{{{
data T a where T :: b ~ Const a => a -> T b
}}}
in order to get the correct error message:
{{{
Couldn't match expected type `b' against inferred type `a1'
`b' is a rigid type variable bound by
the type signature for `coerce' at bug.hs:8:19
`a1' is a rigid type variable bound by
the constructor `T' at bug.hs:10:11
In the expression: y
In a case alternative: T y -> y
In the expression: case T x :: T (Const b) of T y -> y
-- VISUAL --
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1723>
GHC <http://www.haskell.org/ghc/>
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