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(let! compose (\[f g]
(\[x] (f (g x)))))
((compose (+ 1) (+ 2)) 3)
(let! id (\[a] a))
(let! mod (\[n k]
(- n (* k (/ n k)))))
(let! not (\[b]
(match b
true false
false true)))
(let! is-even (\[n]
(match (mod n 2)
0 true
1 false)))
(let! is-odd (compose not is-even))
;; map :: (a -> b) -> [a] -> [b]
(let! map (\[f lst]
(match lst
[]
[]
otherwise
(prepend (f (head lst)) (map f (tail lst))))))
(map (+ 1) [1 2 3])
;; foldr :: (a -> b -> b) -> b -> [a] -> b
(let! foldr (\[f accumulator lst]
(match lst
[]
accumulator
otherwise
(f (head lst) (foldr f accumulator (tail lst))))))
(foldr + 0 [1 2 3])
;; filter :: (a -> Bool) -> [a] -> [a]
(let! filter (\[pred lst]
(match lst
[] []
otherwise (match (pred (head lst))
true
(prepend (head lst) (filter pred (tail lst)))
false
(filter pred (tail lst))))))
(filter is-even [0 1 2 3 4 5])
(let! reverse_ (\[v a]
(let! lazy x (head v))
(let! lazy xs (tail v))
(let! lazy xa (prepend x a))
(match v
[] a
_ (reverse_ xs xa))))
(let! reverse (\[v]
(reverse_ v [])))
(reverse [1 2 3])
(let! flow (\[fs] (foldr compose id (reverse fs))))
(let! pipe (\[x fs] ((flow fs) x)))
(pipe 10 [(+ 1) (+ 2)])
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