48 lines
811 B
OCaml
48 lines
811 B
OCaml
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(* Sec 01, Feb 3 *)
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(* fold (+) 0 [1;2;3;4]
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fold: ( 'a -> 'b -> 'a )
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-> 'a
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-> 'a list
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-> 'b
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We can see this as
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1 + (2 + (3 + (4 + 0)))
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*)
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let rec fold_v1 f i l =
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match l with
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| [] -> i
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| x::rest -> f x (fold_v1 f i rest)
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let string_folder x s = string_of_int x ^ " " ^ s
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(* fold (+) 0 [1;2;3;4]
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as
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((((0 + 1) + 2) + 3) + 4)
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*)
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let rec fold_v2 f i l =
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match l with
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| [] -> i
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| x::rest -> fold_v2 f (f i x) rest
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let rec foldr (f:'a -> 'b -> 'b) (l:'a list) (v:'b) : 'b =
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match l with
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| [] -> v
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| x::xs -> f x (foldr f xs v)
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(* foldl (+) 0 [1;2;3;4]
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as
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((((0 + 1) + 2) + 3) + 4) *)
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let rec foldl f v l =
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match l with
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| [] -> v
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| x::xs -> foldl f (f v x) xs
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let length lst = foldl (fun n x -> n + 1 ) 0 lst
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let sum lst = foldl (+) 0 lst
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