ychr-0.1.0.0: examples/factorial.chr

% A user-defined function: factorial.
%
% Two equations, tried top-to-bottom. The first matches only when the
% argument is the integer 0. The second matches any N and uses a guard
% N > 0 to exclude negatives.
%
% Used by docs/tutorials/04-functions-and-types.md §1 and §2.

:- module(factorial, [compute/2, fun factorial/1]).
:- chr_constraint compute(int, int).
:- function factorial(int) -> int.

factorial(0)         -> 1.
factorial(N) | N > 0 -> N * factorial(N - 1).

compute(N, R) <=> R is factorial(N).