[parenscript-devel] What should PS LOOP do with null collections?

[Daniel Gackle]

That's right. I wonder if there are other places where this
refinement should be introduced?

On Mon, Jul 12, 2010 at 8:13 AM, Vladimir Sedach <vsedach at gmail.com> wrote:

> So what you're proposing is making the implicit sequence type be (or
> array nil), where nil is treated like a zero-length array? I think
> that's a good idea, it will make a lot of things simpler.
>
> Vladimir
>
> 2010/7/12 Daniel Gackle <danielgackle at gmail.com>:
> > I don't know if anyone other than us is using PS LOOP, but we use it
> > heavily since our application is very loop-intensive. A continual source
> > of bugs is looping over a null collection. Say BAR is null. The following
> > will crash:
> >   (ps (loop :for foo :in bar :do (baz foo)))
> > ...because the code expands to include (length bar). This is particularly
> > annoying if you're running the code in CL as well, where looping over
> > a null collection is just fine.
> > We've been dealing with this like so:
> >   (ps (loop :for foo :in (or bar '()) :do (baz foo)))
> > ... but this is ugly and more importantly very brittle, since it means
> > tracking down every crash case-by-case.
> > My question: what does everybody think about making PS LOOP
> > accept null collections and just do nothing in that case? Something
> > about this bothers me. It goes against the philosophy of PS, which
> > declines to pretend that JS arrays are Lisp lists (something I fully
> agree
> > with). But I'm inclined to make an exception in this case because the
> > strict approach is so painful. And this of course raises the
> > analogous question for any PS versions of MAPCAR, MAPC, etc.
> > Daniel
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> >
> >
>
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