Re: difficulty of writing translators

[Andrew Archibald <aarchiba@calum.csclub.uwaterloo.ca>]

Jim Blandy <jimb@red-bean.com> writes:

> If an operation is going to do something weird and expensive, it
> should be syntactically apparent; it could look like a function call,
> for example.

This is perfectly reasonable.  The trick is not letting people
accidentally change the value without running the code.  It seems
valuable to have a standard. 

> I don't see a major advantage to writing:
> 
>     (set! parameter value)          and             parameter
> 
> instead of 
> 
>     (set-parameter! value)          and             (parameter)
> 
> especially since it's clear that the latter might do significant
> work.  The payoff isn't worth the ugliness it adds to the language.

It's worth coming up with a standard, convenient way to do this.

(define PARAMETER-gizmo
   (lambda (what value)
     (begin 
        (define PARAMETER-internal-value (if #f #f))
  	(cond (((equal? what 'get) PARAMETER-internal-value)
               ((equal? what 'set) (set! PARAMETER-internal-value value)))))))

(define set-PARAMETER! (lambda (value) (PARAMETER-gizmo 'set value)))
(define PARAMETER (lambda () (PARAMETER-gizmo 'get #f)))

If I understnad internal defines correctly, this should make the value
of PARAMETER inaccessible from PARAMETER-gizmo...

Anyone have a better suggestion?

Andrew