scheme@(guile-user)> (define (foo2) (define x 7) (defined-symbol? x)) scheme@(guile-user)> (foo2) $2 = #t
On Tue, Apr 16, 2024 at 8:36 AM Damien Mattei <damien.mat...@gmail.com> wrote: > this could not works because the defined-symbol? used in the macro > if-defined return false because at the expansion of the macro the symbol is > not defined. > > Instead at run-time, this works: > > #|kawa:21|# (define (foo2) (define x 7) (defined-symbol? x)) > #|kawa:22|# (foo2) > #t > > On Sun, Apr 14, 2024 at 9:24 AM Damien Mattei <damien.mat...@gmail.com> > wrote: > >> i tried this, that works in some case: >> >> ;; scheme@(guile-user)> (defined-symbol? d) >> ;; ;;; <stdin>:20:17: warning: possibly unbound variable `d' >> ;; $3 = #f >> (define-syntax defined-symbol? >> (syntax-rules () >> ((_ x) (call-with-current-continuation >> (lambda (exit) >> (with-exception-handler >> (lambda (e) >> (display "defined-symbol? : undefined") (newline) >> (exit #f)) ; eval failed => not defined >> (lambda () >> (eval x (interaction-environment)) >> #t))))))) ; eval suceeded => defined >> >> >> ;; scheme@(guile-user)> (define r 2) >> ;; scheme@(guile-user)> (if-defined r 'defined (define r 7)) >> ;; if-defined : where=#t >> ;; $16 = defined >> ;; scheme@(guile-user)> (if-defined t3 'defined (define t3 7)) >> ;; if-defined : where=#f >> ;; scheme@(guile-user)> t3 >> ;; $17 = 7 >> ;; scheme@(guile-user)> (if-defined z (list z) 'not-defined) >> ;; if-defined : where=#f >> ;; $18 = not-defined >> (define-syntax if-defined >> (lambda (stx) >> (syntax-case stx () >> ((_ id iftrue iffalse) >> (let ((where (defined-symbol? #'id))) ;;(quote id)))) >> (display "if-defined : where=") (display where) (newline) >> (display "id=") (display #'id) (newline) >> (if where #'iftrue #'iffalse)))))) >> >> but fais with those examples: >> >> scheme@(guile-user)> (define (foo) (define x 1) (if-defined x 'def >> 'not_def)) >> defined-symbol? : undefined >> if-defined : where=#f >> id=#<syntax:unknown file:37:39 x> >> scheme@(guile-user)> (define (bar) (let ((x 1)) (if-defined x 'def >> 'not_def))) >> defined-symbol? : undefined >> if-defined : where=#f >> id=#<syntax:unknown file:38:39 x> >> >> >> On Fri, Apr 12, 2024 at 1:40 PM Damien Mattei <damien.mat...@gmail.com> >> wrote: >> >>> indeed ,seems not a thing feasible ,unless in Racket where it works >>> great: >>> >>> >>> https://stackoverflow.com/questions/3267351/how-do-i-test-whether-a-variable-is-defined-before-referencing-it?noredirect=1&lq=1 >>> >>> On Fri, Apr 12, 2024 at 12:34 AM Damien Mattei <damien.mat...@gmail.com> >>> wrote: >>> >>>> >>>> hello, >>>> >>>> i'm searching the equivalent in scheme , guile or r6rs of this code for >>>> Racket: >>>> >>>> ; Tests >>>> ;; (if-defined z (list z) 'not-defined) ; -> not-defined >>>> >>>> ;; (if-defined t (void) (define t 5)) >>>> ;; t ; -> 5 >>>> >>>> ;; (define x 3) >>>> ;; (if-defined x (void) (define x 6)) >>>> ;; x ; -> 3 >>>> (define-syntax (if-defined stx) >>>> (syntax-case stx () >>>> [(_ id iftrue iffalse) >>>> (let ([where (identifier-binding #'id)]) >>>> (display "if-defined : where=") (display where) (newline) >>>> (display "id=") (display #'id) (newline)(newline) >>>> (if where #'iftrue #'iffalse))])) >>>> >>>> it is based on identifier-binding >>>> >>>> i tried defined? in guile but it is not reliable other than toplevel, >>>> then i wrote this code based on exception and test the evaluation of the >>>> variable in environment: >>>> >>>> ;; scheme@(guile-user)> (defined-symbol? d) >>>> ;; ;;; <stdin>:20:17: warning: possibly unbound variable `d' >>>> ;; $3 = #f >>>> (define-syntax defined-symbol? >>>> (syntax-rules () >>>> ((_ x) (call-with-current-continuation >>>> (lambda (exit) >>>> (with-exception-handler >>>> (lambda (e) >>>> (display "defined-symbol? : undefined") (newline) >>>> (exit #f)) ; eval failed => not defined >>>> (lambda () >>>> (eval x (interaction-environment)) >>>> #t))))))) ; eval suceeded => defined >>>> >>>> used in conjunction with: >>>> >>>> ;; scheme@(guile-user)> (define r 2) >>>> ;; scheme@(guile-user)> (if-defined r 'defined (define r 7)) >>>> ;; if-defined : where=#t >>>> ;; $16 = defined >>>> ;; scheme@(guile-user)> (if-defined t3 'defined (define t3 7)) >>>> ;; if-defined : where=#f >>>> ;; scheme@(guile-user)> t3 >>>> ;; $17 = 7 >>>> ;; scheme@(guile-user)> (if-defined z (list z) 'not-defined) >>>> ;; if-defined : where=#f >>>> ;; $18 = not-defined >>>> (define-syntax if-defined >>>> (lambda (stx) >>>> (syntax-case stx () >>>> ((_ id iftrue iffalse) >>>> (let ((where (defined-symbol? #'id))) ;;(quote id)))) >>>> (display "if-defined : where=") (display where) (newline) >>>> (display "id=") (display #'id) (newline) >>>> (if where #'iftrue #'iffalse)))))) >>>> >>>> but in some case it fails again >>>> >>>> the goal is to be able to use this macro: >>>> >>>> (define-syntax <- >>>> >>>> (lambda (stx) >>>> >>>> (syntax-case stx () >>>> >>>> ((_ var expr) >>>> >>>> #`(if-defined var >>>> (set! var expr) >>>> (define var expr)))))) >>>> >>>> that define a variable when not defined or just set! it >>>> >>>> it then fails in some case: >>>> >>>> (let () (define k 0) (let loop () (if (< k 4) (let () (display k) >>>> (newline) (<- k (+ k 1)) (loop))))) >>>> defined-symbol? : undefined >>>> if-defined : where=#f >>>> id=#<syntax:unknown file:22:80 k> >>>> #<unspecified> >>>> ice-9/boot-9.scm:1685:16: In procedure raise-exception: >>>> In procedure +: Wrong type argument in position 1: #<unspecified> >>>> >>>> Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue. >>>> >>>> but works in this case: >>>> >>>> scheme@(guile-user)> (define k 0) >>>> scheme@(guile-user)> (let loop () (if (< k 4) (let () (display k) >>>> (newline) (<- k (+ k 1)) (loop)))) >>>> if-defined : where=#t >>>> id=#<syntax:unknown file:25:59 k> >>>> 0 >>>> 1 >>>> 2 >>>> 3 >>>> >>>> i know it is hard and perheaps not possible but if someone has any idea? >>>> >>>> Damien >>>> >>>>
