Maybe monad in Javascript

maybe-monad.js

function maybe(value) {
  var obj = null;
  function isEmpty() { return value === undefined || value === null }
  function nonEmpty() { return !isEmpty() }
  obj = {
    map: function (f) { return isEmpty() ? obj : maybe(f(value)) },
    getOrElse: function (n) { return isEmpty() ? n : value },
    isEmpty: isEmpty,
    nonEmpty: nonEmpty
  }
  return obj;
}

Like it! Was this inspired by Haskell or Scala?

Scala again, I'm still learning me a Haskell

Thought it might have been, I love Scala's type system.

what is the private function nonEmpty() used for?

Oops, it's not supposed to be private. Fixed.

Tasty.

I also love Scala, but I am tired of waiting for compiles, so I'm looking at other FP-friendly languages.

I've been delighted with JS, it's so minimal.

Oh, have you tried Clojure? I know it's another JVM language, but I was very pleased with it.

No, I've seen it and it looks a lot more LISPy than Scala, but I haven't tried it yet.

Yeah, it's a minimal dialect. Have you read this? http://www.defmacro.org/ramblings/lisp.html
I didn't "get" LISP till I read it.

Cheers, that's a nice article. I think I already get LISP, but it never hurts to double check. I'm still not 100% on monads.

The revelation for me was the similarities to XML!

Hi Andy,

Thank you very much for sharing this with us. I just wanted to ask you if it would be ok for you if I use this code in a commercial web app.

Thanks again,
Jose

Check Douglas Crockford's talk in which he explains monads using JavaScript: http://www.youtube.com/watch?v=b0EF0VTs9Dc The Maybe monad is also presented there.

Hi all, thanks for share.
But In my opinion this is not a Monad, instead, it is only a Functor.
A monad should has a function called bind, or, >>=, which call do with a function having type A->M[A]
For Maybe monad, you will like -

    bind: function (f) { return isEmpty() ? obj : f(value) }

Actually, a Monad requires at least two methods: bind and return.

class Monad m where
  (>>=) :: m a -> (a -> m b) -> m b -- aka bind
  return :: a -> m a

Inspired by this, here's an example using es6 and generators https://gist.github.com/torgeir/7618372

No Martini, no party. No bind, no monad. You may call it flatMap, but fixItOrElse("wrong, wrong, wrong")
@ptnplanet in this case return is maybe(value) itself

I think this is just a functor no?

@andyhd just created something similar to this for node called Giftbox here. Would love to hear your thoughts/feedback! Also motivated by Scala :)

@Muzietto, lol ! how true :)