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{-# LANGUAGE MonoLocalBinds, PatternSynonyms, ViewPatterns, TypeAbstractions #-}
module T21501 where
import Data.Kind
import Type.Reflection
pattern TypeApp ::
forall {k1} {k2} (f :: k1 -> k2) (result :: k2).
Typeable f =>
forall (arg :: k1).
result ~ f arg =>
TypeRep arg ->
TypeRep result
pattern TypeApp arg_rep <- App (eqTypeRep (typeRep @f) -> Just HRefl) arg_rep
f :: TypeRep (a :: Type) -> String
f (TypeApp @[] rep) = show rep
{- Expected type: TypeRep k (a::k)
Instantiate at k10 k20 (f0 :: k10 -> k20) (result0 :: k20)
Unify (TypeRep k (a::k) ~ TypeRep k20 (result :: k20)
Unify f0 ~ []
-}
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