On Tue, 9 Apr 2019 at 10:29, David Kastrup <d...@gnu.org> wrote: > Gianmaria Lari <gianmarial...@gmail.com> 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.
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