syntax? in scheme/Guile

syntax? in scheme/Guile

[Damien Mattei]

hello,

any idea for a predicate for syntax object in Guile/scheme like exist in
Racket 'syntax?' ?

i'm started writing something but i do not understand this part of R6RS:

https://www.r6rs.org/final/html/r6rs-lib/r6rs-lib-Z-H-13.html#node_sec_12.2

what examples can be done for :
-

-a nonpair, nonvector, nonsymbol value, or
-

-a wrapped syntax object.
- what is a wrapped syntax object?

Damien


-

Re: syntax? in scheme/Guile

[Damien Mattei]

possible solution:


(define (syntax? obj)

  (cond ; a syntax object is:
   ((pair? obj) ; a pair of syntax objects,
    (and (syntax? (car obj))
	 (syntax? (cdr obj))))
   ((list? obj)
	 (every syntax? obj))
   ((vector? obj) ; a vector of syntax objects
    (every syntax? (vector->list obj)))
   ((string? obj) ; as i will use the string representation of object
    #f)
   ;; parse the representation of object to search for #<syntax something>
   (else (let* ((str-obj (format #f "~s" obj))
		(lgt-str-obj (string-length str-obj))
		(str-syntax "#<syntax")
		(lgt-str-syntax (string-length str-syntax)))
	   (and (> lgt-str-obj lgt-str-syntax) ; first, length greater
		(string=? (substring str-obj 0 lgt-str-syntax)
			  str-syntax) ; begin by "#<syntax"
		(char=? #\> (string-ref str-obj (- lgt-str-obj 1)))))))) ; last char is >


;; scheme@(guile-user)> (syntax? #'(1 . 3))
;; $30 = #t

;; scheme@(guile-user)> (syntax? #'(1 2 3))
;; $28 = #t

;; scheme@(guile-user)> (syntax? #'*)
;; $23 = #t
;; scheme@(guile-user)> (syntax? 3)
;; $24 = #f
;; scheme@(guile-user)> (syntax? "")
;; $25 = #f


On Mon, May 13, 2024 at 10:42 AM Damien Mattei <damien.mattei@gmail.com>
wrote:

> hello,
>
> any idea for a predicate for syntax object in Guile/scheme like exist in
> Racket 'syntax?' ?
>
> i'm started writing something but i do not understand this part of R6RS:
>
> https://www.r6rs.org/final/html/r6rs-lib/r6rs-lib-Z-H-13.html#node_sec_12.2
>
> what examples can be done for :
>
>    -
>
>    -a nonpair, nonvector, nonsymbol value, or
>    -
>
>    -a wrapped syntax object.
>    - what is a wrapped syntax object?
>
>
> Damien
>
>
>
>    -
>
>

Re: syntax? in scheme/Guile

[Thompson, David]

Hi Damien,

On Mon, May 13, 2024 at 4:43 AM Damien Mattei <damien.mattei@gmail.com> wrote:
>
> any idea for a predicate for syntax object in Guile/scheme like exist in
> Racket 'syntax?' ?

This predicate is in the (system syntax) module in Guile.

> - what is a wrapped syntax object?

Syntax objects are part of the syntax-case procedural macro system. A
syntax object wraps a value with things like lexical context and
source location (when available).

For example:

scheme@(guile-user)> (call-with-input-string "(1 2 3)" read-syntax)
$16 = #<syntax:unknown file:1:0 (#<syntax:unknown file:1:1 1>
#<syntax:unknown file:1:3 2> #<syntax:unknown file:1:5 3>)>

See 6.8.3 Support for the ‘syntax-case’ System in the manual.

Hope this helps,

- Dave

Re: syntax? in scheme/Guile

[Damien Mattei]

thank you Dave,

syntax? is enough for the operators like #'* #'+ etc that i  need to test
(even if some complex syntax object are returned #f) :
scheme@(guile-user)> (use-modules (system syntax))
scheme@(guile-user)> syntax?
$1 = #<procedure syntax? (_)>
scheme@(guile-user)> (syntax? #'(2 * 3))
$2 = #f
scheme@(guile-user)> #'(2 * 3)
$3 = (#<syntax:unknown file:6:3 2> #<syntax:unknown file:6:5 *>
#<syntax:unknown file:6:7 3>)
scheme@(guile-user)> (syntax? #'*)
$4 = #t
scheme@(guile-user)> (syntax *)
$5 = #<syntax:unknown file:8:8 *>
scheme@(guile-user)> (syntax? *)
$6 = #f

regards,
damien

On Tue, May 14, 2024 at 1:43 AM Thompson, David <dthompson2@worcester.edu>
wrote:

> Hi Damien,
>
> On Mon, May 13, 2024 at 4:43 AM Damien Mattei <damien.mattei@gmail.com>
> wrote:
> >
> > any idea for a predicate for syntax object in Guile/scheme like exist in
> > Racket 'syntax?' ?
>
> This predicate is in the (system syntax) module in Guile.
>
> > - what is a wrapped syntax object?
>
> Syntax objects are part of the syntax-case procedural macro system. A
> syntax object wraps a value with things like lexical context and
> source location (when available).
>
> For example:
>
> scheme@(guile-user)> (call-with-input-string "(1 2 3)" read-syntax)
> $16 = #<syntax:unknown file:1:0 (#<syntax:unknown file:1:1 1>
> #<syntax:unknown file:1:3 2> #<syntax:unknown file:1:5 3>)>
>
> See 6.8.3 Support for the ‘syntax-case’ System in the manual.
>
> Hope this helps,
>
> - Dave
>