Re: macro definition for continue and break

[Jean Abou Samra <jean@abou-samra.fr>]

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