Re: multi-methods?

[Yaroslav Kavenchuk <kavenchuk at gmail dot com>]

Per Bothner wrote:
> Read section "Procedures" in the manual, and specifically
> look for 'define-procedure'.

I watched.

"Warning: The current implementation of selecting the "best" method is 
not reliable if there is more than one method. It can select depending 
on argument count, and it can select between primitive Java methods. 
However, it cannot yet do what you probably hope for: select between 
different Scheme procedures based on parameter types."
                            ^^^^^^^^^^^^^^^^^^^^^^^^
That stopped me.

> Some example of multi-methods using define-procedure are in
> kawa/lib/numers.scm (in the SVN version).

Many thanks! It is work!

And simple double-dispatch is works:

(define-class Figure ())
(define-class Ball (Figure))

(define-procedure doSomething
  (lambda ((ball :: Ball) (ball :: Ball)) :: void
    (display "Ball-Ball\n"))

  (lambda ((ball :: Ball) (fig :: Figure)) :: void
    (display "Ball-Figure\n"))

  (lambda ((fig :: Figure) (ball :: Ball))  :: void
    (display "Figure-Ball\n"))

  (lambda ((fig :: Figure) (fig :: Figure)) :: void
    (display "Figure-Figure\n")))

(define ball :: Figure (Ball))
(define fig :: Figure (Figure))
(doSomething fig fig)
(doSomething fig ball)
(doSomething ball fig)
(doSomething ball ball)

But it is very dependent on the order of methods.

Many thanks again!

--
WBR, Yaroslav Kavenchuk.