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

[Daniel Gackle]

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mailman.common-lisp.net/pipermail/parenscript-devel/attachments/20100712/042d4950/attachment.html>