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March 1, 2018 13:07
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data Nat = Zero | Suc Nat | |
fromNat :: Nat -> Integer | |
fromNat Zero = 0 | |
fromNat (Suc n) = fromNat n + 1 | |
add :: Nat -> Nat -> Nat | |
add Zero Zero = Zero | |
add Zero n = n | |
add n Zero = n | |
add a (Suc n) = Suc (add a n) | |
mul :: Nat -> Nat -> Nat | |
mul Zero n = Zero | |
mul n Zero = Zero | |
mul a (Suc Zero) = a | |
mul (Suc Zero) a = a | |
mul a (Suc n) = add a (mul a n) | |
fac :: Nat -> Nat | |
fac Zero = Zero | |
fac (Suc Zero) = Suc Zero | |
fac k = facTimes k (Suc Zero) where | |
facTimes Zero acc = acc | |
facTimes x@(Suc n) acc = facTimes n (mul acc x) |
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