Lambda the Ultimate

Of course monads doesn't. Say it is a kind of journalism for Ruby geeks who want to know why Haskellians are so excited about monads without learning Haskell, understanding it's deeper motivations and/or reading Wadlers articles which are quite beautiful but also kind of philosophical. Maybe this is also an affective demystification or expressed more positively: an enlightenment preventing fear ( black magic! ). "Look how simple monads really are", "see what all the buzz is about". We can do so too. One does not really get the point, but what is done out there by weird functionalists in the wilderness doesn't harm us.

Spending some time in programmer communities actually helps in understanding their primitive mentality.

The main intent here is to demystify them, rather than trying to make them useful in Ruby per se.

Not sure I would make cracks about "primitive" mentality, though. Those sorts of issues with the novel are a consistent trait of humanity.

Monads are only less mystical for FPers because they already have the conceptual/cognitive tools to address them. In my case I've also got to subtly include a gentle education in functional programming.

That's far from the only reason functional programmers use monads. For example, they allow control over side-effect propagation via the type system. They also make it possible to build new varieties of side-effect, some of which might be mutually exclusive with others. In fact, working with a customised monad can often feel rather like aspect-oriented programming...

Ruby probably doesn't need monads, at least not in the sense that Haskell needs them. But monads can be used to elegantly express a whole variety of useful programming patterns: nondeterminism, backtracking, exceptions, delimited continuations... Monads provide an excellent framework for transparently threading hidden state through a program. Implementing any of the above examples requires some kind of programming discipline in any case (passing extra arguments, trampolining, special return value conventions, ...), and monads give you a well-understood, structured way to approach that discipline, give you "one place to do it", and can ease the burden on the end programmer. They also come with a whole legacy of useful formal results. Like group theory, once a problem is modeled monadically, you might get a lot of new insight for free.

Besides, Scheme is as imperative as Ruby (where it counts), and monads still come in handy...

Now we have monads in Haskell, ML, Perl, Java, Ruby, and Joy. Did I miss any?

Scheme! (What's wrong with you?!)

How long till we see the first corporate conferences on Monad Oriented Technology?

That won't happen until we see a few monad-related IPOs, and the beginnings of a monad-based stock bubble.

That's embarassing...

Maybe we can get some early venture capital for the first monad-related IPOs? Too bad lexifi decided to use OCaml instead of Haskell for the commercial version of SPJ's financial contracts.

Maybe darcs will have the first monadic IPO?

VB? ;-)

OK, I'll do my best.

MONADIC CONSTRUCTS FOR
LOGIC PROGRAMMING

We describe a variety of logic programming constructs in terms of monads and monad morphisms and a reconstruction of all-solution predicates in terms of list comprehensions in \lambdaProlog. Novel monad structures are described for lazy function lists, clause unfoldings and a monad morphism based embedding of Prolog in \lambdaProlog is given. Not limited to \lambdaProlog, most of our techniques are usable in logic programming languages which implement a call/N built-in.

I saw monads in OCaml. Or does this count as ML ?

for python we have List/Generator Monad Combinators and the shepp example in the comments of this

has continuations to.

(Any suggestions re: the friendlier syntax, by the way? I haven't been able to think of anything particularly good...)

No, but it really seems like it should be there... This is one of my gripes with Ruby... You can play with the syntax, but it doesn't feel too nice. It feels like you're simply overloading existing syntax to mean something new, rather than really extending it (Lua works this way, too). So you have to be very clever to figure out how to sneak your feature into the syntax. With macros, you can design from scratch.

One other question: did you catch my pun in the original post? "Maybe in Part 4"? I thought it was so clever!

Ah, no, I hadn't... I'm afraid I've spent so long thinking about Maybe for chapter 4 that I've experienced a degree of pun-blindness (it lends itself to far too many puns).

As for macros in Ruby, it's possible. ZenSpider's MetaRuby library lets you do AST manipulation, so it's just a matter of someone coding it up.

I might do it myself, except I'm currently distracted with adding lazy evaluation to Ruby.