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{-# LANGUAGE DataKinds #-}
{-# LANGUAGE PartialTypeSignatures #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeOperators #-}
module T12844 where
barWraper :: ('(r,r') ~ Head rngs, Foo rngs) => FooData rngs
barWraper = bar
bar :: (_) => FooData rngs
bar = foo
data FooData rngs
class Foo xs where foo :: (Head xs ~ '(r,r')) => FooData xs
type family Head (xs :: [k]) where Head (x ': xs) = x
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