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  • Glasgow Haskell CompilerGlasgow Haskell Compiler
  • GHCGHC
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  • #7916
Closed
Open
Issue created May 16, 2013 by Krzysztof Gogolewski@monoidalDeveloper

PolyKinds without type signatures

Consider

{-# LANGUAGE PolyKinds, ExplicitForAll #-}
f :: forall (m :: k -> *) (a :: k). m a -> m a
f = id

g = f

I would expect GHC to infer the same type for g as for f. However, it gives the AnyK kind, and g is not possible to use:

ghci -Wall X.hs

...

X.hs:5:1: Warning:
    Top-level binding with no type signature:
      g :: forall (m :: AnyK -> *) (a :: AnyK). m a -> m a
Ok, modules loaded: Main.
*Main> g "a"

<interactive>:2:1:
    Kind incompatibility when matching types:
      a0 :: AnyK
      Char :: *
    In the first argument of ‛print’, namely ‛it’
    In a stmt of an interactive GHCi command: print it
Trac metadata
Trac field Value
Version 7.7
Type Bug
TypeOfFailure OtherFailure
Priority normal
Resolution Unresolved
Component Compiler (Type checker)
Test case
Differential revisions
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