Re: check undefined variable scheme

[Urs Liska]

Am 24.05.2018 um 09:56 schrieb Gianmaria Lari:

The following function increase a counter by 1 and return it as string

#(define count 0) 

#(define (nextcount) (begin

                      (set! count (+ 1 count))

                      (number->string count)

                      )

   )

Is my code ok, or I should write it in a different way?

Two observations:
- You don't need that (begin ...) wrapper because the procedure definition already behaves as such
- You shouldn't use reserved words for variable names, so I'd use 'counter' instead.

Is it possible to define "count" inside the function just in case it is undefined?

Yes, see:

\version "2.19.80"

#(define (nextcount)
   (if (not (defined? 'counter)) (ly:parser-define! 'counter 0))
   (set! counter (+ 1 counter))
   (number->string counter)
   )


#(ly:message "~a" (nextcount))
#(ly:message "~a" (nextcount))

HTH
Urs

Thank you, g.

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