Le sam. 22 déc. 2018 à 09:59, Aaron Hill <[email protected]> a
écrit :
> [...]
> This one looks funny at first, but the difference is the use of the
> grave as opposed to the apostrophe. This sets up a quasi-quoting mode
> that behaves nearly identical to normal quoting, except we can use a
> comma to "unquote". And here the variables will be evaluated as
> expected.
E.g. :
\version "2.18"
#(define-markup-command (double-box layout props xoff yoff) (number?
number?)
(interpret-markup layout props
(markup
(#:with-dimensions (cons 0 0) (cons 0 0)
(#:path 0.3 `(
(moveto ,xoff ,yoff)
(lineto ,(+ xoff 2) ,(+ yoff 4))
(moveto ,(+ xoff 1) ,yoff)
(lineto ,(+ xoff 3) ,(+ yoff 4))))))))
{
a2^\markup\double-box #5 #-2 a
}
Cheers,
Pierre
Le sam. 22 déc. 2018 à 09:59, Aaron Hill <[email protected]> a
écrit :
> On 2018-12-21 8:15 pm, Mike Stickles wrote:
> > But when I try to implement the numbers, I get errors no matter what I
> > do. This (while it doesn't work) shows what I'm trying to get to:
> >
> > #(define-markup-command (double-box layout props xoff yoff) (number?
> > number?)
> > (interpret-markup layout props
> > #{
> > \markup {
> > \with-dimensions #'(0 . 0) #'(0 . 0)
> > \path #0.3 #'((moveto xoff yoff) (lineto (+ xoff 2) (+
> > yoff 4)) (moveto (+ xoff 1) yoff) (lineto (+ xoff 3) (+ yoff 4)))
> > }
> > #}
> > ))
> >
> >
> > Any ideas on what I'm doing wrong?
>
> You are hitting an common stumbling block in Scheme regarding quoting.
> Urs has a great Scheme introduction book[1] online that would be good
> reviewing as it sounds like you may be relatively new to the language.
>
> [1]: https://scheme-book.ursliska.de/
>
> \path needs a list of commands, where an individual command consists of
> a symbol (defining the particular command) and then its arguments, which
> are typically just numbers.
>
> To construct a suitable \path argument in Scheme, we use the list
> function:
>
> (list ((quote moveto) 1 2) ((quote lineto) 3 4))
>
> This is the explicit list construction technique, and we are also using
> the explicit invocation of quote. We need quote here because "moveto"
> and "lineto" are symbols. We do not want the value behind the symbols,
> just the symbols as things on their own.
>
> Scheme (technically LISP) developed a number of shorthands for common
> constructions. You can construct a list more succinctly this way:
>
> '((moveto 1 2) (lineto 3 4))
>
> The leading quote puts us in quote mode so that we can simply type
> "moveto" by itself. We also no longer need to say list explicitly, as
> we'll end up with a list. The numbers are technically being quoted
> here, but a quoted number literal works.
>
> But what if we need a variable? We cannot use the same construction,
> because our variables will end up quoted rather than using the value
> behind the name. One solution is to go back to the more explicit
> invocation:
>
> (list ('moveto a b) ('lineto c d))
>
> Here we are still using the shortcut quote for the symbols, but
> everything else will be resolved properly in this form. This is a
> perfectly acceptable option, but some folks prefer the shorthand of
> quoting. The alternate solution is quasi-quoting:
>
> `((moveto ,a ,b) (lineto ,c ,d))
>
> This one looks funny at first, but the difference is the use of the
> grave as opposed to the apostrophe. This sets up a quasi-quoting mode
> that behaves nearly identical to normal quoting, except we can use a
> comma to "unquote". And here the variables will be evaluated as
> expected.
>
>
> -- Aaron Hill
>
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> lilypond-user mailing list
> [email protected]
> https://lists.gnu.org/mailman/listinfo/lilypond-user
>
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