monads.js

// need an algebraic data structure 
// a..e are defined as meta param names
// f variable will hold all the declared Algebraic Data Types

newdata("Maybe", function(spec){
  // the data constructor name as key
  // the parameters specified as an array
  spec["Just"] = [a];
  spec["Nothing"] = [];
});

classtype("Monad", function(spec) {
  // spec will have the different methods of a classtype
  // each attribute is a function that could have default
  // implementations
  spec['_bindAction'] = function(monad, fn) {
    this.bind(monad, function(_) {
      return fn();
    }
  };
  spec['bindAction'] = function() {};
  spec['inject'] = function() {};
});

function lookupPerson(id) {
  if (id === 12345) {
    return f.Just("Roman");
  }
  else {
    return f.Nothing;
  }
}

function lookupNumber(person) {
  if (person === "Roman") {
    return f.Just("555-5555");
  }
  else {
    return f.Nothing;
  }
}

// to make an Algebraic Data Type or a newtype an instance
// of a classtype
classtypeInstance("Monad", "Maybe", {

  bindAction: function(maybe, fn) {
    maybe.match({
      'Just': function(x) { return fn(x); },
      'Nothing': function() { return f.Nothing; }
    });
  },

  inject: function(a) {
    return f.Just(a);
  }

});

// to declare
function() { 
  lookupPerson(12345).bindAction(function(person) {
    return lookupPhone(person);
  });
});