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  • Glasgow Haskell CompilerGlasgow Haskell Compiler
  • GHCGHC
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  • #14420
Closed
Open
Issue created Nov 03, 2017 by Richard Eisenberg@raeDeveloper

Data families should not instantiate to non-Type kinds

data family Any :: k  -- allowable now due to fix for #12369

type family F (a :: Bool) :: Nat where
  F True  = 0
  F False = 1
  F Any   = 2
ghci> :kind! F True
F True :: Nat
= 0
ghci> :kind! F False
F False :: Nat
= 1
ghci> :kind! F Any
F Any :: Nat
= 2

Oh dear.

We should require that any instantiation of a data family be to a kind that ends in Type.

Inspired by ticket:9429#comment:144757

Trac metadata
Trac field Value
Version 8.3
Type Bug
TypeOfFailure OtherFailure
Priority normal
Resolution Unresolved
Component Compiler
Test case
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