Please, list object-oriented systems with objects with identities and object-ori...

babel17 · on May 31, 2011

Message passing does require a sender, a receiver, and a message. You can have those in purely functional programming. No identity needed. But if you really want one, you can have it: Two objects are identical, if they react to all messages in the same way. You can also explicitly define equality ==, and then say that a and b are identical if a == b.

thesz · on June 1, 2011

>Message passing does require a sender, a receiver, and a message. You can have those in purely functional programming. No identity needed.

Would you mind show me some code in pure functional language?

I mean, in Haskell or Clean. Those are pure enough.

loup-vaillant · on June 1, 2011

http://www.loup-vaillant.fr/articles/classes-as-syntactic-su...

My Ocaml code is not pure, but we can easy remove any occurrence of `ref`, and restricting oneself to pure methods, which produce a new fresh object instead of modifying `this` in place.

thesz · on June 2, 2011

Sorry, I am not very fluent in OCaml. Also, I didn't find word "message" in the link above.

I am experiencing limitations of pure objects and message passing almost right now. In my spare time I am currently developing dynamic data flow CPU which is based on immutable "objects" and message sending. It is quite unusual style of programming, very unlike anything else, including Smalltalk, Erlang and everything.

loup-vaillant · on June 2, 2011

It's like Haskell, with a slightly heavier syntax. And it's eager. And you can unsafePerformIO all over the place (but avoid doing so even in Ocaml).

    (* Ocaml *)    --Haskell
    let foo = 42   foo = 42    -- top level declaration
    type bar =     data bar =  -- type declaration

Also, records in Ocaml are a separate kind of type, more like C structs:

    type bar = { x:int;     (* defination *)
                 y:float;
               }
    bar.x                   (* "member" acces *)

"Message passing" and "Method calling" are strictly equivalent, at least when everything is synchronous.