either.js

var R = require('ramda');

// isLeft :: Either a b -> bool
var isLeft = function(val) {
    return val.chain(R.identity) === val;
};

// isLeft :: Either a b -> bool
var isRight = R.compose(R.not,isLeft);

// either :: Either a b -> (a -> c) -> (b -> c) -> c
var either = function(x, leftF, rightF) {
    return isRight(x) ? x.chain(rightF) : leftF(x.value);
};

module.exports.either = either;
module.exports.isLeft = isLeft;
module.exports.isRight = isRight;