#7026: Impredicative implicit parameters
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Reporter: Ashley Yakeley | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (Type
checker)
Version: 7.4.2 | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: GHC rejects valid program | Testcase:
Blockedby: | Blocking:
Related: |
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There doesn't seem to be a way to make impredicative implicit parameters
work in 7.4.2:
{{{
{-# LANGUAGE ImplicitParams, ImpredicativeTypes #-}
module Bug where
f1 :: Maybe ((?a :: Bool) => Char)
f1 = Just 'C'
f2 :: Maybe ((?a :: Bool) => Bool)
f2 = Just ?a
}}}
{{{
$ ghc -c Bug.hs
Bug.hs:5:15:
Couldn't match expected type `(?a::Bool) => Char'
with actual type `Char'
In the first argument of `Just', namely 'C'
In the expression: Just 'C'
In an equation for `f1': f1 = Just 'C'
Bug.hs:8:15:
Unbound implicit parameter (?a::(?a::Bool) => Bool)
arising from a use of implicit parameter `?a'
In the first argument of `Just', namely `?a'
In the expression: Just ?a
In an equation for `f2': f2 = Just ?a
}}}
I believe this used to work?
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7026>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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