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%%
%% Sieve of eratosthenes to compute primes
%% thom fruehwirth 920218-20, 980311
%% christian holzbaur 980207 for Sicstus CHR
%%
%% ported to hProlog by Tom Schrijvers 

:- module(primes,[primes/0]).
:- use_module(library(chr)).

:- chr_constraint candidate/1.
:- chr_constraint prime/1.
:- chr_constraint cleanup/1.

:- chr_option(debug,off).
:- chr_option(optimize,full).

candidate(1) <=> true.
candidate(N) <=> prime(N), N1 is N - 1, candidate(N1).

absorb @ prime(Y) \ prime(X) <=> 0 =:= X mod Y | true.

cleanup(_L), candidate(_X) <=> fail.
cleanup(L), prime(N) <=> L = [N|T], cleanup(T).
cleanup(L) <=> L = [].

primes :-
	candidate(100),
	cleanup(L),
	sort(L,SL),
	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].