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Ethiopian multiplication: Difference between revisions
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</lang>
=={{header|CHR}}==
This is a CHR solution for this problem using Prolog as the host language. Code will work in SWI-Prolog and YAP (and possibly in others with or without some minor tweaking).
<lang prolog>:- module(ethiopia, [test/0, mul/3]).
:- use_module(library(chr)).
:- chr_constraint multiply/3, mul/3, halve/2, double/2, even/1, add_odd/4.
mul(1, Y, S) <=> S = Y.
mul(X, Y, S) <=> X \= 1 | halve(X, X1),
double(Y, Y1),
mul(X1, Y1, S1),
add_odd(X, Y, S1, S).
halve(X, Y) <=> X = 1 | Y = 1.
halve(X, Y) <=> X > 1 | Y is X // 2.
double(X, Y) <=> Y is X * 2.
even(X) <=> 0 is X mod 2 | true.
even(X) <=> 1 is X mod 2 | false.
add_odd(X, _, A, S) <=> even(X) | S is A.
add_odd(X, Y, A, S) <=> \+ even(X) | S is A + Y.
test :-
mul(17, 34, Z), !,
writeln(Z).</lang>
=={{header|Clojure}}==
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