You just need to tell Factor the expected stack effect.
See, this fails to compile, because the quotation is only selected at
run-time and the compiler isn't smart enough to examine both:
: foo ( seq -- seq' )
dup length even? [ 1 - ] [ 2 + ] ? map ;
But, you can always do something like this where you tell Factor to call
the quotation with the expected stack effect:
: foo ( seq -- seq' )
dup length even? [ 1 - ] [ 2 + ] ?
'[ _ call( elt -- elt' ) ] map ;
I think that might incur some run-time performance penalties because it
would check the stack effect on every call, which doesn't matter for your
use-case, but might if it was inside a hot loop.
Best,
John.
On Fri, Feb 3, 2017 at 4:25 PM, Alexander Ilin <ajs...@yandex.ru> wrote:
> Hello!
>
> I'm developing my chart gadget. I want to achieve this:
>
> ALIAS: x first
> ALIAS: y second
>
> : chart-axes ( chart -- seq )
> [ dim>> ] [ axes>> ] bi [
> nip
> ] [
> [ 0 swap 2array ] map
> ] if* ;
>
>
> M: axis draw-gadget*
> dup parent>> dup chart? [| axis chart |
> axis vertical?>> :> vert?
> chart dim>> :> dim
> dim chart chart-axes vert? [ [ x ] bi@ ] [ [ y ] bi@ ] if
> ! etc...
> ] [ 2drop ] if ;
>
> I thought I found a clever way to simplify that `if` there:
>
> dim chart chart-axes vert? [ x ] [ y ] ? bi@
>
> But the compiler says that I can't use `call` on runtime-computed
> quotations. Is there a way to work around that, like, by using a MACRO: or
> something?
>
> Or is this a hard limitation on the available abstraction of the
> computation?
>
> Basically, depending on a boolean flag I need to either take the first
> or the second element of the two arrays on the stack, and place the taken
> elements on the stack in the same order.
>
> ---=====---
> Александр
>
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