Re: macro definition for continue and break

["Linus Björnstam" <linus.internet@fastmail.se>]

If you want a bit more advanced looping you could have a look at my goof-loop: https://git.sr.ht/~bjoli/goof-loop

It currently does not support a break or continue clause, but adding one should not really be a problem.

A good thing is that it does not rely on mutation for anything except higher order sequences, meaning it does not lead to the implicit boxing overhead of set!, which is a good idea in loops since that quickly adds up.

Best regards 
  Linus Björnstam

On Sun, 4 Sep 2022, at 13:13, Jean Abou Samra wrote:
> Hi,
>
> Adding back the list in CC.
>
>
> Le 04/09/2022 à 12:49, Damien Mattei a écrit :
>> hello jean,
>> yes (thank you for your help) i'm a sorcerer's apprentice that always 
>> push to later the understanding of literals in syntax-rules, but by 
>> instinct i finally succeed in making works the weird thing :-) , here 
>> is my macro definition now for a for with break and continue:
>>
>> (define-syntax for
>>
>>   (lambda (stx)
>>     (syntax-case stx ()
>>       ((kwd (init test incrmt) body ...)
>>
>>        (with-syntax
>>         ((BREAK (datum->syntax #'kwd 'break))
>>          (CONTINUE (datum->syntax #'kwd 'continue)))
>>
>>        #`(call/cc
>>             (lambda (escape)
>>                 (let-syntax
>>                      ((BREAK (identifier-syntax (escape))))
>>                   init
>>                  (let loop ()
>>                         (when test
>>
>>                            #,#'(call/cc
>>                                     (lambda (next)
>>                                        (let-syntax
>>                                             ((CONTINUE 
>> (identifier-syntax (next))))
>>                                            body ...)))
>>
>>                                     incrmt
>>                                     (loop)))))))))))
>>
>> note the mysterious #,#' that save the day ;-)
>
>
> For me, it works without it… ?
>
>
>> and a few examples (in Scheme+)
>>
>> ;; scheme@(guile-user)> (for ({i <+ 0} {i < 5} {i <- {i + 1}}) {x <+ 
>> 7} (display x) (newline) (break))
>> ;; 7
>> ;; scheme@(guile-user)> (for ({i <+ 0} {i < 5} {i <- {i + 1}}) {x <+ 
>> 7} (continue) (display x) (newline) (break))
>> ;; scheme@(guile-user)>
>>
>> ;; (for ({k <+ 0} {k < 3} {k <- {k + 1}})
>> ;;      (display k)
>> ;;      (newline)
>> ;;      (for ({i <+ 0} {i < 5} {i <- {i + 1}}) {x <+ 7}
>> ;;            (display x)
>> ;;            (newline)
>> ;;            (break))
>> ;;      (newline))
>>
>> ;; 0
>> ;; 7
>>
>> ;; 1
>> ;; 7
>>
>> ;; 2
>> ;; 7
>>
>> ;; (for ({k <+ 0} {k < 3} {k <- {k + 1}})
>> ;;      (display k)
>> ;;      (newline)
>> ;;      (continue)
>> ;;      (for ({i <+ 0} {i < 5} {i <- {i + 1}}) {x <+ 7}
>> ;;         (display x)
>> ;;         (newline)
>> ;;         (break))
>> ;;     (newline))
>>
>> ;; 0
>> ;; 1
>> ;; 2
>>
>> https://github.com/damien-mattei/library-FunctProg/blob/master/for-next-step.scm
>>
>> it also works with imbricated loops in a natural way (but other 
>> interpretation and implementation could be  done , C act like this ,i 
>> think)
>> but if it could be coded better i will use a better version
>
>
> Yes, it can be done better; see my reply on the other thread.
>
>
> Best,
> Jean