// unary
var unary = function (apply) {
    return function (arg) {
        return function (x, y, z) {
            return apply(arg(x, y, z));
        };
    }
};

var variable = function (name) {
    return function (x, y, z) {
        switch (name) {
            case 'x': {
                return x;
            }
            case 'y': {
                return y;
            }
            case 'z': {
                return z;
            }
        }
    }
};

var cnst = function (value) {
    return function (x) {
        return value;
    }
};

var negate = unary(
    function (arg) {
        return -arg;
    }
);

var cube = unary(
    function (arg) {
        return Math.pow(arg, 3);
    }
);

var cuberoot = unary(
    function (arg) {
        return Math.pow(arg, 1.0 / 3);
    }
);

// binary
var binary = function (apply) {
    return function (left, right) {
        return function (x, y, z) {
            return apply(left(x, y, z), right(x, y, z));
        };
    }
};

var add = binary(
    function (left, right) {
        return left + right;
    }
);

var subtract = binary(
    function (left, right) {
        return left - right;
    }
);

var multiply = binary(
    function (left, right) {
        return left * right;
    }
);

var divide = binary(
    function (left, right) {
        return left / right;
    }
);