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TEST OF DEFACTORISATION FOR FUNCTIONS THAT DROP
POLYMORPHIC VARIABLES
> 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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