#7916: PolyKinds without type signatures --------------------------------------+------------------------------------- Reporter: monoidal | Owner: Type: bug | Status: new Priority: normal | Component: Compiler (Type checker) Version: 7.7 | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: GHC rejects valid program | Blockedby: Blocking: | Related: --------------------------------------+------------------------------------- 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 }}} -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7916 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler