#7194: Typechecker allows a skolem to escapt
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Reporter: simonpj | Owner:
Type: bug | Status: closed
Priority: normal | Milestone:
Component: Compiler | Version: 7.4.2
Resolution: fixed | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: None/Unknown | Difficulty: Unknown
Testcase: | Blockedby:
Blocking: | Related:
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Changes (by igloo):
* status: new => closed
* resolution: => fixed
Comment:
This now gives a type error:
{{{
T7194.hs:18:35:
Couldn't match expected type `b0' with actual type `F a'
because type variable `a' would escape its scope
This (rigid, skolem) type variable is bound by
the type signature for g :: C (F a) => a -> Int
at T7194.hs:17:23-41
Relevant bindings include
x :: b0 (bound at T7194.hs:17:9)
g :: a -> Int (bound at T7194.hs:18:18)
y :: a (bound at T7194.hs:18:20)
In the return type of a call of `foo'
In the expression: foo y
In the first argument of `length', namely `[x, foo y]'
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7194#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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