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-- !! TEST OF DEFACTORISATION FOR FUNCTIONS THAT DROP
-- !! POLYMORPHIC VARIABLES
module Test where
data Boolean = FF | TT
data Pair a b = MkPair a b
data LList alpha = Nill | Conss alpha (LList alpha)
data Nat = Zero | Succ Nat
data Tree x = Leaf x | Node (Tree x) (Tree x)
data A a = MkA a (A a)
append :: LList a -> LList a -> LList a
append xs ys = case xs of
Nill -> ys
Conss z zs -> Conss z (append zs ys)
-- The following function drops @b@.
flat :: Tree (Pair a b) -> LList a
flat t = case t of
Leaf (MkPair a b) -> Conss a Nill
Node l r -> append (flat l) (flat r)
fl :: Boolean -> LList Boolean
fl x = flat (Leaf (MkPair TT Zero))
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