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{-# LANGUAGE GeneralizedNewtypeDeriving #-}
-- Don't do the cunning new newtype-deriving thing
-- when the type constructor is recursive
module Main where
newtype A = A [A] deriving (Eq)
-- The derived instance would be:
-- instance Eq A where
-- (A xs) == (A ys) = xs==ys
-- $df :: Eq [A] => Eq A
-- $df d = d |> Eq (sym co)
x :: A
x = A [A [], A [A []]]
main = print (x == x)
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