Re: [Chicken-users] fixnum-specific math operators patch

[felix winkelmann]

On 9/1/06, Will M Farr <address@hidden> wrote:
> 3. My opinion is that The Right Thing (TM) is to code the macro as
> follows:
>
> (define-syntax do-range
>    (syntax-rules ()
>      ((_ (i aa bb) expr ...)
>       (let ((a aa)
>            (b bb))
>         (cond-expand
>         ((not unsafe)
>          (if (or (not (fixnum? a))
>                  (not (fixnum? b)))
>              (error 'do-range "non-fixnum limits" a b))))
>         (do ((i a (fx+ i 1)))
>            ((fx= i b))
>          expr ...)))))
>
> This works, but it's pretty yucky.  It is the simplest way, given the
> present behavior of the fxXXX operators, to achieve safety in safe
> mode (with useful, and immediate, error reporting) and speed in
> unsafe mode.  I submitted the fixnum patch because it would implement
> the same behavior, but without requiring people using the fxXXX
> operators to think so much about these issues (and type (cond-
> expand ...) every time).

Using something like "ensure" can help here:

% cat x.scm
(define x 33)
(print (ensure fixnum? x))
% csc x.scm -debug 2 && ./x
[canonicalized]
(set! c2 '"argument has incorrect type")
(##core#callunit "library")
(##core#callunit "eval")
(##core#callunit "extras")
(##core#undefined)
(##core#undefined)
(set! x '33)
(print (let ((g01 x))
        (if (fixnum? g01)
          g01
          (##sys#signal-hook type-error: c2 g01 'fixnum?))))
((##sys#implicit-exit-handler))
(##core#undefined)
33
% csc x.scm -debug 2 -unsafe && ./x
[canonicalized]
(set! c2 '"argument has incorrect type")
(##core#callunit "library")
(##core#callunit "eval")
(##core#callunit "extras")
(##core#undefined)
(##core#undefined)
(set! x '33)
(print (let ((g01 x))
        (if '#t g01 (##sys#signal-hook type-error: c2 g01 'fixnum?))))
((##sys#implicit-exit-handler))
(##core#undefined)
33

(Note that the "if" expression will be folded to "g01")


cheers,
felix

--
http://galinha.ucpel.tche.br:8081/blog/blog.ssp