Thomas Morley <thomasmorle...@gmail.com> writes:
> Hi all,
>
> (1)
> consider the following code (working as expected):
>
> \paper {
> #(if #t (set-paper-size "a8" 'landscape) #(set-paper-size "a8"))
> }
>
> \score { { R1 } \layout { ragged-right = ##f } }
>
> Switching from #t to #f results in different paper-size, as desired.
Unlikely as you write #(set-paper-size ...) here, see below.
>
> (2)
> But trying to put it in a procedure, it always returns the true-case:
>
> #(define (proc bool x y)
> (if bool x y))
>
> \paper {
> #(proc #f (set-paper-size "a8" 'landscape) #(set-paper-size "a8"))
> }
Uh, the return value is irrelevant. It always _executes_ the true case.
It also executes the false case but that is not overly interesting since
the false case is a vector consisting of the elements 'set-paper-size
and "a8" since you write #(...) while already in Scheme, the syntax for
vector literals.
Now if you want to execute only conditionally, you either need to wrap
in lambdas or use a macro rather than a procedure:
#(define-macro (proc bool x y)
(if bool x y))
\paper {
#(if #t (set-paper-size "a8" 'landscape) (set-paper-size "a8"))
}
Note that this will only work with a _literal_ #f or #t as argument:
you'll likely want to have some actual condition evaluated at runtime,
like some variable name. Then you'll need to write
#(define-macro (proc bool x y)
`(if ,bool ,x ,y))
--
David Kastrup
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