Damien Mattei schreef op do 23-09-2021 om 19:27 [+0200]:
> yes i know parsing the whole code is the only portable solution, but it is slow,even on a few dozen of lines the slowing is visible ,so i can even think of that on one thousand lines...
> 
> I finally succeed in Guile with simple piece of code to make my example run with a single assignment operator <-  , here i define for variable the assignment operator <$ , <- is working with arrays too:
> 
> Preview:
> 
> (define-syntax <$
>   
>   (lambda (s)
>     
>     (syntax-case s ()
>       
>       ((_ var value)
>        
>        (case (syntax-local-binding #'var)
> 	 
>          ((lexical) #'(begin
> 			(display "<$ : lexical scope : ")
> 			(display (quote var))
> 			(newline)
> 			(set! var value)))
> 	 
> 	 ((displaced-lexical) #'(begin
> 				  (display "<$ : displaced-lexical scope : ")
> 				  (display (quote var))
> 				  (newline)
> 				  (set! var value)))
> 	 
>          ((global) #'(begin
> 		       (display "<$ : global scope : ")
> 		       (display (quote var))
> 		       (newline)
> 		       (define var value)))
> 	 
>          (else #'(begin
> 		   (display "<$ : unknow variable scope :")
> 		   (display (quote var))
> 		   (error "<$ : unknow variable scope : "))))))))
> 
> 
> it allows this Scheme+ code to run with a single assignment operator (note in some case the operator is also a definition of variable,but it is invisible for the programmer, it has the duality of define and set!):
> 
> Preview:
> 
> (define (subset-sum-guile L t)
> 
>   {ls <- (length L)}
>   {dyn <- dyna[ls t]}
> 
> ;; dyna[ls][t] means 0: unknown solution, 1: solution found, 2: no solution
>   
>   (condx [{dyn <> 0} (one? dyn)]
> 	 [(null? L) {dyna[ls t] <- 2}  #f] ;; return #f
> 	 
> 	 [exec {c <- (first L)}]	 
> 	 ;; c is the solution
> 	 [{c = t} {dyna[ls t] <- 1}  #t]  ;; return #t
> 	 
> 	 [exec {R <- (rest L)}]	 
> 	 ;; continue searching a solution in the rest
> 	 [{c > t} {s <- (subset-sum-guile R t)}
> 	          {dyna[ls t] <- (one-two s)}
> 		  s] ;; return boolean value
> 			
> 	 ;; else : c < t at this point
> 	 ;; c is part of a solution OR not part of a solution
> 	 [else {s <- {(subset-sum-guile R {t - c}) or (subset-sum-guile R t)}}
> 	       {dyna[ls t] <- (one-two s)}
> 	       s])) ;; return boolean value
> 
>      
> 
> some people were sceptic about the possibility to make it, but it works, i do not say it is portable code.
> 
> When i run the program with debug i see that:
> scheme@(guile-user)> (subset-sum-guile  L-init t-init)
> <$ : global scope : ls
> <$ : global scope : dyn
>  
> <$ : global scope : c
> <$ : global scope : R
> <$ : global scope : s
> <$ : global scope : ls
> <$ : global scope : dyn
>  
> <$ : global scope : c
> .... hundreds of lines.....
> #t
> 
> all variable are global,

No, they are local, even though syntax-local-binding returns 'global'.
'syntax-local-binding' doesn't know we will be defining a local variable
with the same name later, so it says 'global' instead of 'lexical' or
'displaced-lexical'.

There is no such thing as ‘global to the body of the function’, what you are
descrbing is local variables.

The macro <$ you have defined won't work for the "hello world" example I sent
you:

(define (#{hello/won't-work}# language)
  (cond ((equal? language "dutch")
         (<$ message "Hallo wereld"))
        ((equal? language "english")
         (<$ message "Hello world")))
  (display message)
  (newline))
While compiling expression:
Syntax error:
unknown file:70:9: definition in expression context, where definitions are not allowed, in form (define message "Hallo wereld")

The following does, however:

(define (hello language)
  (<$ message #f)
  (cond ((equal? language "dutch")
         (<$ message "Hallo wereld"))
        ((equal? language "english")
         (<$ message "Hello world")))
  (display message)
  (newline))

Possibly this limitation of <$ is acceptable to you though.

> but they are just global to the body of the function,not at toplevel,so there is no risk of breaking the code logic it is just that if we want to see lexical scope we need a more nested example,it is strange because i thought that the condx macro creates nestled code for each conditional clauses...
> 
> to see the lexical scope we can use this example:
> scheme@(guile-user)> 
> (condx [exec {k <- 1}]
>     [{k = 1} {k <- {k + 1}} {k + 1}]
>     [else 'never])
> <$ : global scope : k
> <$ : lexical scope : k
> $3 = 3
> here the lexical scope is well visible :-)
> but if k had existed at toplevel it is not modified :-( :
> scheme@(guile-user)> (define k 0)
> scheme@(guile-user)> 
> (condx [exec {k <- 1}]
>            [{k = 1} {k <- {k + 1}} {k + 1}]
>            [else 'never])
> <$ : global scope : k
> <$ : lexical scope : k
> $4 = 3
> scheme@(guile-user)> k
> $5 = 0
> 
> :-(
>  probably beause syntax-local-binding only works in the current lexical environment ?
> https://www.gnu.org/software/guile/docs/master/guile.html/Syntax-Transformer-Helpers.html
> but not at toplevel ???
> Scheme Procedure: syntax-local-binding id [#:resolve-syntax-parameters?=#t]
> Resolve the identifer id, a syntax object, within the current lexical environment
> 
> for this reason i still searching a solution that would be a mix of syntax-local-binding and Module System Reflection .

Use the second return value of syntax-local-binding.
Or just use set! instead of <$ and <- to modify global variables,
and use <- and <$ for local variables only.

Greetings,
Maxime.