Impredicative implicit parameters
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?
Trac metadata
Trac field | Value |
---|---|
Version | 7.4.2 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler (Type checker) |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |