Erlangで素数と素数でないものを分けてリストを返す

Erlangの修行中。erlangで特定の数字を入れると、素数と合成数で分けて、それぞれが入ったlistを返すというものを作った。

Source

- module(primenum).
- export([primenum/1, printnum/2]).

primenum(Num) when Num >= 2 ->
        primecheck(2, Num);
primenum(_Others) ->
        false.

primecheck(TargetNum, TargetNum) ->
        true;
primecheck(Num, TargetNum) when TargetNum rem Num =:= 0 ->
        false;
primecheck(Num, TargetNum) ->
        primecheck(Num+1, TargetNum).


createlist(Num, List) when Num == 0 ->
        List;
createlist(Num, List) ->
        createlist(Num-1 ,[Num | List]).


printnum(Num, Type) when Type =:= "Prime" ->
        List = createlist(Num, []),
        PrimeNum = lists:filter(fun(X) -> primenum(X) end, List);
printnum(Num, Type) when Type =:= "Composit" ->
        List = createlist(Num, []),
        PrimeNum = lists:filter(fun(X) -> primenum(X) end, List),
        CompositNum = List -- PrimeNum.

実行結果

2> primenum:printnum(100, "Prime").
[2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,
 79,83,89,97]
3> primenum:printnum(100, "Composit").
[1,4,6,8,9,10,12,14,15,16,18,20,21,22,24,25,26,27,28,30,32,
 33,34,35,36,38,39,40,42|...]