ychr-0.1.0.0: examples/gcd.chr

% Euclid's algorithm as two CHR rules.
%
% Tell gcd(N) for each input number; the rules repeatedly replace the
% larger of two numbers with their difference and drop zeros, until a
% single gcd(G) remains in the store.
%
% Used by docs/explanation/what-is-chr.md.

:- module(gcd, [gcd/1]).
:- chr_constraint gcd/1.

zero     @ gcd(0) <=> true.
subtract @ gcd(N) \ gcd(M) <=> M >= N, N > 0 | gcd(M - N).