Hello Trygve,

You reproduced the mechanism of Lisp for resolving variable. This means that in Lisp, whenever you write the name of a variable, you do not know statically to which variable you are referring to. Whereas in Scheme, as in Smalltalk, you can statically determine to which variable a name is bound.

For instance, in Lisp you would write:
(defun a 5)
(defun f () a)
(let ((a 10))
  (f))  ;  ===> 10
(let ((a 20))
  (f))  ;  ===> 20

Whereas in Scheme, a similar code would yield:
(define a 5)
(define (f) a)
(let ((a 10))
  (f))  ; ===> 5
(let ((a 20))
  (f))  ; ===> 5

Cheers,
Alexandre

On Sat, May 14, 2005 at 11:41:45AM +0200, Trygve Reenskaug wrote:
> In BabyUML, I am experimenting with a very dynamic namespace that is put on 
> the stack, that exists during the execution of a block, and that is visible 
> to all methods called directly or indirectly from the block.
> 
> It seems to work using the exeception mechanism, but I would appreciate 
> assistance to check if I am doing something ugly or dangerous.
> 
> The namespace class is called Map and is a subclass of Exception.
> 
> I create aMap with the desired contents and put it on the stack with:
> 
>       [body statements] on: aMap do: [:ex | ].
> 
> Any method called from the body statements get hold of the map by this 
> method:
> 
>   map
>     | ctx map |
>     ctx := thisContext.
>     [ ctx := ctx findNextHandlerContextStarting.
>         ctx isNil or: [(map := ctx tempAt: 1) isKindOf: DNetMap]
>     ] whileFalse: [ctx := ctx sender].
>     ^ctx
>         ifNil: [self error: 'No map found.'. nil]
>         ifNotNil: [map]
> 
> Many thanks for any tips or guidance.
> --Trygve
> 
> (If this works, it illustratesthe extreme power of Squeak)
> 
> 
> -- 
> 
> Trygve Reenskaug      mailto: trygver at ifi.uio.no
> Morgedalsvn. 5A       http://heim.ifi.uio.no/~trygver
> N-0378 Oslo           Tel: (+47) 22 49 57 27
> Norway
> 
> 

-- 
_,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:
Alexandre Bergel  http://www.iam.unibe.ch/~bergel
^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;.