Am 24.05.2018 um 10:46 schrieb David Kastrup:
Urs Liska <li...@openlilylib.org> writes:
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)
)
You actually don't need to define it externally:
#(define nextcount
(let ((counter 0))
(lambda ()
(set! counter (1+ counter))
(number->string counter))))
$(nextcount)
$(nextcount)
will work just fine.
Ah yes, that's more idiomatic and (thus) elegant.
Gianmaria, if you want to understand what's happening there read
https://www.gnu.org/software/guile/docs/docs-1.8/guile-ref/Closure.html#Closure
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