[plt-scheme] Re: current-eval is now ready to receive anything...

On 3/5/07, Ryan Culpepper <ryan_sml at yahoo.com> wrote:
> --- "Paulo J. Matos" <pocm at soton.ac.uk> wrote:
>
> > Sorry... pressed Send,  when I should have pressed Save...
> > The message continues below...
> >
> > On 3/5/07, Paulo J. Matos <pocm at soton.ac.uk> wrote:
> > > Hi all,
> > >
> > > By preparing current-eval to receive more than just
> > syntax-objects as
> > > stated in docs (which I quoted in my last post but
> > mis-interpreted)
> > > can I know before hand which things may be passed to current-eval
> > > besides what the user types in and their type?
> > > My guess is that when the user types something it is sent in the
> > form
> > > of syntax object to current-eval, except the s-expr
> > (current-namespace (module->namespace 'test))
> >
> > Up until now I was not able to find any exception to this rule.
> > Is there anything more I should know?
>
> The module-name-resolver calls the current evaluator on the compiled
> code for a module the first time a module is required. And the 'eval'
> procedure just passes along whatever it is given:
>
>   (define old-evaluator (current-eval))
>   (define (evaluator x)
>     (cond [(and (syntax? x) (compiled-expression? (syntax-e x)))
>            (display "evaluating compiled code wrapped in syntax\n")]
>           [(syntax? x)
>            (display "evaluating syntax\n")]
>           [(compiled-expression? x) (display "evaluating compiled
> code\n")]
>           [else (display "evaluating S-expression\n")])
>     (old-evaluator x))
>
>   (begin (current-eval evaluator)
>
>          ;; the module-name-resolver calls eval
>          ;; on the contents of the .zo file
>          (require (lib "cmdline.ss"))
>
>          ;; 'eval' just passes argument along
>          (void (eval '(lambda (x) x)))
>          (void (eval (compile '(lambda (x) x)))))
>

Nice idea on fallbacking to the previous evaluator in case custom
evaluator cannot eval expression. Thank you! :-)

> Ryan
>
> > _________________________________________________
> >   For list-related administrative tasks:
> >   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
> >
>
>
>
>
> ____________________________________________________________________________________
> Need a quick answer? Get one in minutes from people who know.
> Ask your question on www.Answers.yahoo.com
>
>
>


-- 
Paulo Jorge Matos - pocm at soton.ac.uk
http://www.personal.soton.ac.uk/pocm
PhD Student @ ECS
University of Southampton, UK