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{-# LANGUAGE TypeFamilies #-}
module TH_tf1 where
$( [d| data family T a |] )
$( [d| data instance T Int = TInt Bool |] )
foo :: Bool -> T Int
foo b = TInt (b && b)
$( [d| type family S a |] )
$( [d| type instance S Int = Bool |] )
bar :: S Int -> Int
bar c = if c then 1 else 2
$( [d| type family R (a :: * -> *) :: * -> * |] )
$( [d| type instance R Maybe = [] |] )
baz :: R Maybe Int -> Int
baz = head
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