Gianmaria Lari <address@hidden> writes:
> Ciao Harm, Andrew, Aaron and David,
>
> this is what I have been able to do adapting Harm code:
>
> \version "2.21.0"
> foo =
> #(let ((x '(1)))
> (define-scheme-function (arg)(symbol?)
> (case arg
> ((incNumber) (set! x (append (drop-right x 1) (list (1+ (last x))))))
> ((unindent) (drop-right! x 1))
> ((indent) (append! x '(1)))
> ((reset) (set! x '(1))))
> (object->string x)))
Harm did not accidentally write (let ((x (cons 1 0))) ... here. '(1) is
a _constant_ list where you guarantee to the Scheme interpreter that you
will not modify any cons cell of the list and it can place it in
read-only memory. If now the next call is 'indent , this guarantee is
violated, possibly leading to crashes and inconsistencies in shared
constants. Then you use append! and drop-right! for list manipulation
and rely on their side effects to do what you want. Those side effects
are optional. This is rather bad Scheme code. What are the goals you
intend to achieve with those changes?
The reason why I changed Harm code was because it was not clear to me the use of cons. Furthermore mine looked simpler :)
Thank you David for pointing me out the problem. I will read better his code and the documentation about cons.
Ciao, g.