Maybe.js

Maybe.js

class Maybe {
  
  constructor(val) {
    this.val = val;
  }
  
  map(f) {
    return this.val ? new Maybe(f(this.val)) : new Maybe();
  }
  toString() {
    return 'Maybe('+this.val+')';
  }	
}

// Syntactic suga
var map = (f, obj) => obj.map(f);

/* Named mapping functions to test with */
var log = (val) => console.log("%s", val);
var toLower = (val) => val.toLowerCase();

var first = (xs) => {
	if(!xs) return null;
	else return xs[0];
};

var debug = (fn) => {
  return (val) => {
	var fnName = fn.name || 'fn';
	var res = fn(val);
	console.log('debug: ' + fnName + '('+val+') = ' + res);
	return res;
  }
};

var prop = (key) => {
  return (obj) => {
    if(obj[key]) {
      return obj[key];
    }
    return null;
  };
}
var username = prop('username');

var isAuthed = true;
function getUser() {
	if(isAuthed) {
		return new Maybe({username: "snichme", email: "mange@mange.name"});
	} else {
		return new Maybe();
	}
}

console.log();
console.log("isAuthed = " + isAuthed);
map(log, map(username, getUser()));
map(log, map(prop('email'), getUser()));
isAuthed = false;
console.log("isAuthed = " + isAuthed);
map(log, map(username, getUser()));

console.log();
console.log();

// Example
map(log, map(debug(toLower), new Maybe("Firstname Lastname")));

 

map(log, map(toLower, new Maybe()));
map(log, map(debug(first), new Maybe("Firstname Lastname")));
map(log, map(first, new Maybe()));
map(log, map(first, new Maybe(['A', 'B', 'C'])));
map(log, map(debug(toLower), new Maybe("Username Username")));
map(log, map(first, map(toLower, new Maybe("Username Username")))); 

var me = new Maybe("Magnus Andersson");
me.map(debug(toLower)).map(log);


['A', 'B'].map(debug(toLower)).map(log);

map(log, map(debug(toLower), ['A', 'B', 'C']));