Damien Mattei schreef op di 21-09-2021 om 15:04 [+0200]: > i have tested define-once > http://www.gnu.org/software/guile/docs/master/guile.html/Top-Level.html > (the defvar of Lisp)and idea are: > -unfortunately it is considered by scheme as a define,so there is some > context where it is not allowed in my code > -seems to work fine at toplevel (as mentioned in doc) but strange behavior > in a function, i did not understand really what happened but i got some > #unspecified value. > > here are my test code: > cheme@(guile-user)> (define (foo2) > (define-once x 1) > (if #t > (let () > (define-once x 2) > ;;(set! x 2) > (display "x=") > (display x) > (newline)) > 'never) > (display x) > (newline)) Possibly you want (added a set? argument for demonstration): (define (foo2 set?) (define x) ; define an (undefined or unbound, not sure about terminology) variable (if set? (let () (set! x 2) ; change the value of x (display "x=") (display x) (newline)) 'never) (display x) (newline)) That should be portable and avoids global state. scheme@(guile-user)> x ;;; :20:0: warning: possibly unbound variable `x' ice-9/boot-9.scm:1685:16: In procedure raise-exception: Unbound variable: x scheme@(guile-user) [1]> ,q scheme@(guile-user) [1]> (foo2 #f) # ; I expected an error as would result from ... ;; ... this ... scheme@(guile-user)> (variable-ref (make-undefined-variable)) ice-9/boot-9.scm:1685:16: In procedure raise-exception: In procedure variable-ref: Unbound variable: #> Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue. scheme@(guile-user) [2]> ;; instead of # but whatever ... scheme@(guile-user) [1]> (foo2 #t) x=2 2 scheme@(guile-user) [1]> (foo2 #t) x=2 2 scheme@(guile-user) [1]> (define x 3) scheme@(guile-user) [1]> (foo2 #t) x=2 ; foo2 doesn't use the global variable 'x' 2 scheme@(guile-user) [1]> x $1 = 3 Does this seem reasonable to you?