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|
{-# LANGUAGE UnliftedDatatypes #-}
{-# OPTIONS_GHC -fwarn-incomplete-patterns #-}
module Lib where
import Data.Kind (Type)
import GHC.Exts (UnliftedType)
type Foo :: UnliftedType -> Type -> Type
data Foo a b =
Bar a -- no need for strictness annotation
| Baz b
type MyVoid :: UnliftedType
data MyVoid
v :: Foo MyVoid Char
v = Baz 'c'
main :: IO ()
main = case v of
-- The Baz case is impossible
-- MyVoid has no values, and it can't
-- be undefined because it's unlifted.
Baz c -> putChar c
|
