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Possible type inference regression: "Expected a type, but 'a' has kind 'k0'"

    • Closed Issue created by takano-akio @takano-akio

    The following program causes GHC HEAD to give an error:

    {-# LANGUAGE ScopedTypeVariables #-}
module Foo where

foo (_ :: p a) = [] :: [a]
    [1 of 1] Compiling Foo              ( kind.hs, kind.o )

kind.hs:4:25: error:
    • Expected a type, but ‘a’ has kind ‘k0’
    • In an expression type signature: [a]
      In the expression: [] :: [a]
      In an equation for ‘foo’: foo (_ :: p a) = [] :: [a]

    GHC 7.10.1 compiles it fine, and infers the type foo :: p a -> [a].

    Trac metadata
    Trac field Value
    Version 8.1
    Type Bug
    TypeOfFailure OtherFailure
    Priority normal
    Resolution Unresolved
    Component Compiler (Type checker)
    Test case
    Differential revisions
    BlockedBy
    Related
    Blocking
    CC
    Operating system
    Architecture
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