In OOP you instead solve your problem by trying to neatly partition it into lots of little bits of state and specifying how each little bit reacts to changes. As the comment explains, OOP programs are often clumsier than functional ones because OOP enshrines scaffolding in the form of the class hierarchy and method/message dispatch model.

So when is OOP a good idea?

I tend to think that it boils down to the size and organization of your team, the number of independent "architects" in your system and how they are managed.

In a small team this should not be an issue and you're probably better off with a functional approach and perhaps rolling your own messaging scheme like the one in the article if you think you need one.

However in a large team you not only have to deal with whatever problem you're working on, you also have to deal with the secondary problems of how the developers interact with each other. The OOP scaffolding pg makes fun of is one way to make managing a larger team easier since it helps the developers play nicely, stick to their little part of the system and stay out of each others way. It's not the only way, but it is relatively popular in part because it allows some management decisions to be directly expressed in the class hierarchy and programming language.

5. Object-oriented abstractions map neatly onto the domains of certain specific kinds of programs, like simulations and CAD systems.

Also for things like instance creation and method dispatch, OO languages can easily be both faster and more concise than functional languages. In a performance-sensitive setting like a desktop gui or a window system this can easily decide the issue.

But while simulation and OOP do have an important historic relationship, I don't believe you actually gain any special modeling expressiveness by making your objects adhere to a "class" framework. What's worse, the hardcoded assumptions OO languages make about classes and methods can confuse the assumptions in a simulation (e.g. because you can implement an "IS-A" relationship with inheritance doesn't mean you should).

If you want objects in a functional setting, you can just create the appropriate "factory" functions and have those functions return "objects" (i.e. functions with state in closures) which dispatch "methods" however you want them to, just like Jim Rankin did in the article at the top of the thread.

I think that describing certain things, e.g. a windowing system, in terms of classes and objects does result in a useful description. "My window contains a button and a text field" maps nicely to an OO model. The implementation can (perhaps should) be user-level and/or functional with closures, but that modeling system can be powerful.

I was negligent in citing prior work. I had SICP in mind when I wrote my code.

The main differences are I wrapped it all up in a macro, I supported inheritance, and "method invocations" require one less set of parentheses:

    (define acc (make-account 100))
    ((acc 'withdraw) 50)
    50
    ((acc 'withdraw) 60)
    "Insufficient funds"
    ((acc 'deposit) 40)
    90
    ((acc 'withdraw) 60)
    30

First, how many comments do you count in my code?

Second, I think my class definitions are pretty concise, as class definitions go.

Third, Paul said somewhere he doesn't use objects but does use hash tables filled with closures. That is precisely what my objects are. It just provides a brief syntax for defining them. If there is a way to define hash tables filled with closures with even greater brevity I'm all for it.

Fourth, Arc has opened the door to data in functional position and I find that a huge win over other Lisps. I think this should be available to those hacking with Arc, not just the language designer. Maybe another way of saying this is give hackers the ability to create new types and define what they do in functional position and defining "setters" that work with =. Objects are one paradigm for doing that but if there's a better, more Arc-ish way that would be awesome, too.

Fifth, I think this can be a pedagogically useful example to someone coming from, say, Python or Ruby to Arc. I believe that it can help bridge the understanding gap between objects on the one hand and first-class-functions + anonymous functions + closures on the other.

   make-meth

all rely (through coroutines, lambdas, side effects) on the list to know how to be iterable. If you change from a cons list to an array/file/socket/prime generator it will still work.