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{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE ScopedTypeVariables #-}
module T9750 where
import GHC.TypeLits ( Symbol, KnownSymbol )
--------------------------------------------------------------------------------
data Meta = MetaCons Symbol
data M1 (c :: Meta) = M1
class Generic a where
type Rep a :: *
from :: a -> Rep a
--------------------------------------------------------------------------------
data A = A1
instance Generic A where
type Rep A = M1 ('MetaCons "test")
from A1 = M1
class GShow' f where
gshowsPrec' :: f -> ShowS
instance (KnownSymbol c) => GShow' (M1 ('MetaCons c)) where
gshowsPrec' = error "urk"
instance GShow' A where
gshowsPrec' = gshowsPrec' . from
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