Thomas Morley <thomasmorle...@gmail.com> writes:
> 2018-05-19 9:45 GMT+02:00 David Kastrup <d...@gnu.org>:
>> Thomas Morley <thomasmorle...@gmail.com> writes:
>
> Uh, oh, another typo/oversight.
> Note to self: Don't post anything while being overtired...
>
>>
>> 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"))
>> }
Talk about type/oversight: I don't even use the proc macro here. You
need to write it instead of "if" in the paper block, or the example does
not make a whole lot of sense.
>> 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))
>
> Thanks for the insights,
The last bit is a whole lot of quasiquote obviously equivalent to
(list 'if bool x y)
But in the context of macro expansions, using quasiquotes is sort of
customary for emphasizing the structure of what gets returned rather
than how it is getting built.
--
David Kastrup
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