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{-# LANGUAGE GADTs, PatternSynonyms, ViewPatterns, ScopedTypeVariables #-}
module T19847 where
import Data.Kind
import Type.Reflection
pattern Is :: forall (b :: Type) (a :: Type). Typeable b => (a ~ b) => TypeRep a
pattern Is <- (eqTypeRep (typeRep @b) -> Just HRefl)
where Is = typeRep
def :: TypeRep a -> a
def x = case x of
Is @Int -> 10
Is @Bool -> False
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