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2%%
3%% Sieve of eratosthenes to compute primes
4%% thom fruehwirth 920218-20, 980311
5%% christian holzbaur 980207 for Sicstus CHR
6%%
7%% ported to hProlog by Tom Schrijvers
8
9:- module(primes,[primes/0]).
10:- use_module(library(chr)).
11
12:- chr_constraint candidate/1.
13:- chr_constraint prime/1.
14:- chr_constraint cleanup/1.
15
16:- chr_option(debug,off).
17:- chr_option(optimize,full).
18
19candidate(1) <=> true.
20candidate(N) <=> prime(N), N1 is N - 1, candidate(N1).
21
22absorb @ prime(Y) \ prime(X) <=> 0 =:= X mod Y | true.
23
24cleanup(_L), candidate(_X) <=> fail.
25cleanup(L), prime(N) <=> L = [N|T], cleanup(T).
26cleanup(L) <=> L = [].
27
28primes :-
29	candidate(100),
30	cleanup(L),
31	sort(L,SL),
32	SL == [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].
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