Re: scheme set list function

[Gianmaria Lari]

Ciao Harm, Andrew, Aaron and David,

this is what I have been able to do adapting Harm code:

\version "2.21.0"

foo =

#(let ((x '(1)))

  (define-scheme-function (arg)(symbol?)

    (case arg

      ((incNumber) (set! x (append (drop-right x 1) (list (1+ (last x))))))

      ((unindent) (drop-right! x 1))

      ((indent) (append! x '(1)))

      ((reset) (set! x '(1))))

    (object->string x)))

\markup \foo #'start %output: 1

\markup \foo #'indent %output: 1 1

\markup \foo #'incNumber %output: 1 2

\markup \foo #'incNumber %output: 1 3

\markup \foo #'incNumber %output: 1 4

\void \foo #'unindent

\markup \foo #'incNumber %output: 2

(the output formatting is not correct, just an example).

From my side it can be improved to make it more user friendly (maybe checking "start" etc.) but they are details. 

I will spend some time to understand if the definition of x outside the define-scheme-function is the correct way to do (is this is a closure?)

* * *

I read all the technical discussion, interesting but definitely too far from what I understand at the moment of the language.

* * *

I didn't yet check the new code you sent Harm, 

[harm code]

#(define (increase lst idx)

  (if (and (positive? idx) (<= idx (length lst)))

      (let ((tmp-lst (take-right lst idx)))

        (cons (1+ (car tmp-lst)) (cdr tmp-lst)))

      (begin

        (ly:warning

  "idx ~a is not positive or list ~a does not contain enough elements, ignoring"

          idx lst)

        lst)))

[.....]

... but I'm doing it today! Thanks a lot!!!

Ciao, gianmaria