A stack effect of ( seq quot -- ) doesn't say what the quot is expected to
do...
You can play around with it and see how it works:
IN: scratchpad "abc" [ "empty" ] when-empty .
"abc"
IN: scratchpad "" [ "empty" ] when-empty .
"empty"
We should improve the docs here because they are a little hard to follow,
since it refers to ``when-empty`` taking the "first quot" of an
``if-empty``, with an empty second quot.
On Wed, Mar 1, 2017 at 8:18 AM, Alexander Ilin <ajs...@yandex.ru> wrote:
> Hello!
>
> I'm struggling with some of the Factor's words. Mostly with
> `when-empty`, `if-zero` and similar. It's difficult for me to understand
> why they don't work sometimes, while their simpler counterparts (while, if)
> do work exactly as expected.
>
> Here's the latest installment of my struggle:
>
> IN: scratchpad USE: crypto.xor [ [ empty-xor-key ] when-empty ] infer.
> ( x -- x )
>
> Why is the stack effect as shown here? The documentation for
> `when-empty` says it takes `( seq quot -- )`. Therefore, I expect `[ [
> empty-xor-key ] when-empty ] infer.` to output `( x -- )`.
>
> When I modify the quotation passed to `when-empty` to be a no-op, I get
> a compilation error:
> IN: scratchpad [ [ 1 drop ] when-empty ] infer.
> Error
> The input quotations to “if-empty” don't match their expected effects
> Input Expected Got
> [ 1 drop ] ( ..a -- ..b ) ( -- )
> [ ] ( ..a seq -- ..b ) ( -- )
>
> That's completely weird to me. Is the stack effect in the documentation
> incorrect? Should it be `( seq quot -- seq )`?
> And why does it refuse to compile the second example with `1 drop`?
>
> ---=====---
> Александр
>
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