Pointfree fantasy working with folktale's either

pointfree folktale.js

require("pointfree-fantasy").expose(global);
var curry = require("lodash.curry");
var fs = require("fs");
var Either = require("data.either");


// HELPERS
// ============
var add = curry(function(x,y) { return x + y });

var exists = function(path) {
	return fs.existsSync(path);
};

var fread = function(path) {
	return fs.readFileSync(path, 'utf-8');
};


// ACTUAL EXAMPLE
// ===============

// Returns the contents of the file at `path`, if it exists.
//
//  read : String -> Either(Error, String)
function read(path) {
  return exists(path) ? Either.Right(fread(path)) : Either.Left("Non-existing file: " + path);
}

var intro = read('intro.txt')  // => Right(...)
var outro = read('outro.txt')  // => Right(...)
var nope  = read('nope.txt')   // => Left("Non-existing file: nope.txt")

var r = liftA2(add, intro, outro)

console.log('r', r); // => Right(...)

var r1 = liftA2(add, intro, nope)

console.log('r1', r1); // => Left("Non-existing file: nope.txt")