ychr-0.1.0.0: examples/traffic.chr

% An algebraic type with three constructors, plus a typed function
% that pattern-matches on them.
%
% The `intensity_of/2` constraint computes the intensity associated
% with each color and binds it to its second argument.
%
% Used by docs/tutorials/04-functions-and-types.md §2.

:- module(traffic, [intensity_of/2, type(color/0, [red, green, yellow])]).
:- chr_type color ---> red ; green ; yellow.
:- chr_constraint intensity_of(color, int).
:- function intensity(color) -> int.

intensity(red)    -> 100.
intensity(yellow) -> 60.
intensity(green)  -> 20.

intensity_of(C, R) <=> R is intensity(C).