30 lines
746 B
OCaml
30 lines
746 B
OCaml
type 'a lazystream = Cons of 'a * 'a lazystream Lazy.t
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let hd (Cons (h, _)) = h
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let tl (Cons (_, t)) = Lazy.force t
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let rec from n = Cons (n, lazy (from (n + 1)))
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let rec take n (Cons (h, t)) =
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if n <= 0 then []
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else h :: take (n - 1) (Lazy.force t)
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let rec drop n (Cons (h, t) as s) =
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if n <= 0 then s
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else drop (n - 1) (Lazy.force t)
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let rec map f (Cons (h, t)) =
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Cons (f h, lazy (map f (Lazy.force t)))
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let rec map2 f (Cons (h1, t1)) (Cons (h2, t2)) =
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Cons (f h1 h2, lazy (map2 f (Lazy.force t1) (Lazy.force t2)))
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let rec fibs =
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Cons (0, lazy (Cons (1, lazy (map2 (+) fibs (tl fibs)))))
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let rec unfold f x =
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let (v, x') = f x in
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Cons (v, lazy (unfold f x'))
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let fibs' = unfold (fun (a, b) -> (a, (b, a + b))) (0, 1)
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