[Chicken-janitors] Re: #114: Improvements to tinyclos

[Chicken Trac]

#114: Improvements to tinyclos
---------------------------+------------------------------------------------
 Reporter:  tonysidaway    |       Owner:  tonysidaway
     Type:  task           |      Status:  accepted   
 Priority:  major          |   Milestone:             
Component:  extensions     |     Version:  4.2.x      
 Keywords:  tinyclos clos  |  
---------------------------+------------------------------------------------

Comment(by tonysidaway):

 Something like this:
 {{{
 (define (make-a-heap-of-useful-classes)
   (let-generic (pos-x pos-y move resize radius width height)
     (let*-class ((<pos> () (x y))
                  (<circle> (<pos>) (radius))
                  (<oblong> (<pos>) (width height)))
       (define-method (move (p <pos>) x y)
         (and
          (or (not (or (not x) (number? x)))
              (not (or (not y) (number? y))))
          (error "move <pos>: args must be #f or numeric"))
        (and x (slot-set! p 'x x))
        (and y (slot-set! p 'y y)))
       (define-method (resize (c <circle>) (r <number>))
         (slot-set! c 'radius r))
       (define-method (resize (o <oblong>) (w <number>) (h <number>))
         (slot-set! o 'w w)(slot-set! o 'h h))
       (define-method (pos-x (p <pos>) (slot-ref p 'x))
       (define-method (pos-y (p <pos>) (slot-ref o 'y))
       (define-method (pos-x-set! (p <pos>) (x <number>))
         (slot-set! p 'x x))
       (define-method (pos-y-set! (p <pos>) (y <number>))
         (slot-set! p 'y y))
       (define-method (radius (c <circle>)) (slot-ref c 'radius))
       (define-method (width (o <oblong>)) (slot-ref o 'width))
       (define-method (width-set! (o <oblong>) (w <number>)
         (slot-set! o 'width w))
       (define-method (height-set! (o <oblong>) (h <number>)
         (slot-set! o 'height h))
       (define-method (height (o <oblong>)) (slot-ref o 'height))
       (values (list <pos> <circle> <rectangle>)
               (list pos-x pos-x-set! pos-y pos-y-set! move
                     resize radius height)))))
 }}}
 Why go through all that?  Because it encloses all the crap you have to go
 through to make those useful classes.  The calling procedure doesn't need
 to know about generics, classes and whatnot, it doesn't even need to know
 about tinyclos.  It only needs to know how to do the usual Scheme things:
 call a procedure and handle the results.  Possibly even a cleverly written
 macro could receive the results and blend them in;

 {{{
 (define-classes make-a-heap-of-useful-classes)
 (let ((p (make <pos>)))
   (move p 10 20)
   (move p #f (+ (pos-y p) 7)))
 }}}

 define-class semantics as used above are a little crude--there's no way to
 hide the symbolic links to the slots.  It would be good to enable hiding
 of slots so that a truly encapsulated class system could be written.
 There's nothing to stop the programmer using make-class, of course, and
 that would make it easy to do that.  But there ought to be a simple,
 unmessy way to do it all.  A renaming scheme for slots would do that I
 suppose.

-- 
Ticket URL: <http://www.irp.oist.jp/trac/chicken/ticket/114#comment:6>
Chicken Scheme <http://www.call-with-current-continuation.org/>
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