a markov chain

markov.js

(function () {
    'use strict';

    function State(properties) {
        var self = this;
        this.name = properties.name;
        this.transitions = properties.transitions;
    }

    State.prototype.validate = function () {
        var result = (this.transitions.reduce(function (out, next) {
            return out + next.probability;
        }, 0))
        return result === 1.0 || (function () {throw Error('transitions probability must sum to 1.0');})();
    };

    State.prototype.tick = function () {
        this.validate();
        var rn = Math.random();
        return (function loop(result, rest, n0) {
            var n1, hit;
            if (result) {
                return result.target;
            } else if (n0 > 1) {
                throw Error('please correct this.validate();');
            }

            n1 = n0 + rest[0].probability;
            hit = (n0 < rn && rn <= n1) ? rest[0] : null;
            return loop(hit, rest.slice(1), n1);
        })(null, this.transitions, 0);
    };

    function Transition(properties) {
        this.target = properties.target;
        this.probability = properties.probability;
    }


    var stateA = new State({
        name: 'A',
        transitions: []
    });
    var stateB = new State({
        name: 'B',
        transitions: []
    });

    stateA.transitions = [
        new Transition({
            target: stateA,
            probability: 0.5
        }),
        new Transition({
            target: stateB,
            probability: 0.5
        })
    ];

    stateB.transitions = [
        new Transition({
            target: stateB,
            probability: 0.5
        }),
        new Transition({
            target: stateA,
            probability: 0.5
        })
    ];

    state = stateA;

    var list = function (elementCount) {
        return new Array(elementCount).join(' ').split(' ');
    };

    list(10).forEach(function main() {
        var result = list(100).map(function () {
            return (state = state.tick()).name;
        });
        var a = result.filter(function (t) {return t === 'A'});
        var b = result.filter(function (t) {return t === 'B'});
        console.log('A', a.length, 'B', b.length, result.join(''));
    });
})();