Only primes numbers filter in OCAML
Submitted by fabio on Sat, 2007-12-08 14:56.
A small OCAML algorithm to filter out non prime number from a list of given numbers.
(*
Fabio Varesano - 2007/05/11
Delete non prime numbers from a list of integers
(The list must start from 2 and contains all numbers)
*)
let primefilter list =
match list with
| [] -> []
| x::xs -> let primetest = function y -> y mod x <> 0
in x::(List.filter primetest xs);;
primefilter [2;3;4;5;6;7;8;9;10;11;12;13;14;15;16;17;18;19;20;21;22];;
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let rec primefilter list =
let rec primefilter list = match list with
| [] -> []
| x::xs -> let primetest = function y -> y mod x <> 0
in x::(List.filter primetest (primefilter xs));;
# primefilter [2;3;4;5;6;7;8;9;10;11;12;13;14;15;16;17;18;19;20;21;22];;
- : int list = [2; 3; 5; 7; 11; 13; 17; 19]
This returns [2; 3; 5; 7; 9;
This returns [2; 3; 5; 7; 9; 11; 13; 15; 17; 19; 21];;
and last time I checked, 9, 15, and 21 are composite :)
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