2018-05-19 0:36 GMT+02:00 Aaron Hill <lilyp...@hillvisions.com>:
> On 2018-05-18 14:24, Thomas Morley wrote:
>> #(define (proc bool x y)
>> (if bool x y))
> Your `proc` function does not have this behavior, as the arguments passed in
> will be evaluated before you get to the inner `if`.
Hm, then I should reword my request.
Is there a way to circumvent this behaviour?
I'm finally aiming at a function selecting from different set-whatever!
> Now, `set-paper-size`
> has a side-effect, so the evaluation of that function alone is enough to
> have an impact. Technically, the function should be named
> `set-paper-size!`, as the convention is to suffix an exclamation to indicate
> such functions.
>
> So, calling `proc` with the two functions results in both being evaluated,
> which is not what you want.
Ok, then another example for this would be:
#(define (proc bool x y)
(if bool x y))
#(define lst #f)
#(proc #f (set! lst '(1 2)) (set! lst '(3 4)))
#(write lst)
always returns:
'(3 4)
>
> Your `apply` approach is closer to what you want, since you are using `proc`
> as a means of selecting the arguments you want and calling `set-paper-size`
> only once. This should work, except you have an extra quote.
>
> %%%%
> #(apply set-paper-size (proc #t '("a8" landscape) '("a8")))
> %%%%
>
> The outer quote for invoking the list shorthand already results in
> `landscape` being a symbol. The extra quote would put another layer of
> indirection, which `set-paper-size` does not expect.
Ok, it's an overside then.
Thanks for spotting it.
>
> Hope this helps,
>
> -- Aaron Hill
It helped a lot.
Many thanks,
Harm
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