sandbox-functor.js

var Sandbox = function(val, err){
  this.val = val;
  this.err = err;
}

Sandbox.prototype.map = function(fn){
  if ( this.err ) return this;

  try {
    return new Sandbox(fn(this.val));
  } catch(e) { 
    return new Sandbox(undefined, e)
  }
}

Sandbox.prototype.get = function(defaultCase){
  if ( ! defaultCase ) throw Error('default required');
  if ( this.err ) return defaultCase;
  else return this.val;
}