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{-# LANGUAGE FlexibleContexts, MultiParamTypeClasses, FlexibleInstances #-}
module T13526 where
class C a where
op :: a -> a
instance {-# OVERLAPPING #-} C [Char] where
op x = x
instance C a => C [a] where
op (x:xs) = [op x]
instance C a => C (Maybe a) where
op x = error "urk"
-- We should get no complaint
foo :: C [a] => a -> [a]
foo x = op [x]
bar :: C (Maybe a) => a -> Maybe a
bar x = op (Just x)
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