2015-03-15 22:07 GMT+01:00 Thomas Morley <[email protected]>:
>
>
> 2015-03-15 21:48 GMT+01:00 Kevin Barry <[email protected]>:
>
>> Hi LilyPond experts,
>>
>> I'm trying to make a function that will draw a curved line given only a
>> destination point (with some math I'll add later), but I've hit an early
>> stumbling block: I can't seem to substitute variables for values in the
>> path/curveto command list. The following code produces a
>> `wrong-argument-type' error, but it points to scm/stencil.scm which isn't
>> very helpful for figuring out what's wrong. Help appreciated!
>>
>> \version "2.18.2"
>>
>> #(define-markup-command (draw-curved-line layout props points)
>> (number-pair?)
>> (let ((xpt (car points))
>> (ypt (cdr points)))
>> (interpret-markup layout props
>> (markup #:path 1 '((curveto 0 ypt 0 ypt xpt ypt))))))
>>
>> \relative {
>> b_\markup { \draw-curved-line #'(5 . 5) }
>> }
>>
>>
> Hi Kevin,
>
> in cases where i have no clue what's wrong and don't understand the
> error-message, I boil down the code and display all kind of data, values,
> ets
>
> In your case I'd do:
>
> #(define-markup-command (draw-curved-line layout props points)
> (number-pair?)
> (let ((xpt (car points))
> (ypt (cdr points)))
>
> (display '((curveto 0 ypt 0 ypt xpt ypt)))
> (newline)
> (display (caddar '((curveto 0 ypt 0 ypt xpt ypt))))
> (newline)
> (display (symbol? (caddar '((curveto 0 ypt 0 ypt xpt ypt)))))
>
>
> (interpret-markup layout props
> (markup
> ;#:path 1 '((curveto 0 ypt 0 ypt xpt ypt))
> "xy"
> ))
> ))
>
>
>
> The problem should be clear now: the variables in '((curveto 0 ypt 0 ypt
> xpt ypt)) are not evaluated but taken as symbols.
> You wrote a quoted list, but need some elements of the list be unquoted.
> Shortest: use a combi of ` and ,
>
>
> #(define-markup-command (draw-curved-line layout props points)
> (number-pair?)
> (let ((xpt (car points))
> (ypt (cdr points)))
> (interpret-markup layout props
> (markup
> #:path 1 `((curveto 0 ,ypt 0 ,ypt ,xpt ,ypt))
>
other syntax-possibilities:
(list (list 'curveto 0 ypt 0 ypt xpt ypt))
or most verbose:
(quasiquote
((curveto 0 (unquote ypt) 0 (unquote ypt) (unquote xpt) (unquote ypt))))
Look up 'quote', 'unquote', 'quasiquote' etc in the guile manual
))))
>
>
>
> HTH,
> Harm
>
>
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