On 6/3/07, Jonathan Lang <[EMAIL PROTECTED]> wrote:
Chas Owens wrote:
> Jonathan Lang wrote:
> > Chas Owens wrote:
> > > Jonathan Lang wrote:
> > > > Is there any reason why we can't simply define '$a x $n' as being
> > > > shorthand for 'cat($a xx $n)'? In what way does the former differ
> > > > from the latter, other than the use of a Whatever in place of $n?
> > >
> > > "$a x $n" is equivalent to "join '', $a xx $n", but that isn't an apt
> > > description of its behavior. "cat($a xx *)" is an attempt to provide
> > > an infinite string since 'a' x Inf would result in memory overflow
> > > (but the cat trick works since lists are evaluated lazily).
> >
> > Then it looks to me like 'cat($a xx $n)' is more flexible than "join
> > '', $a xx $n", and would work better as the baseline definition for
> > '$a x $n'. Is there any reason to prefer a join-based definition to a
> > cat-based one? AFAICT, the only thing that 'join' can do that 'cat'
> > can't is to provide a delimiter when stitching the component strings
> > together; in the case of 'x', this feature is (rightfully) not being
> > used.
>
> Okay, maybe my understanding of the cat function is flawed, but I
> thought it walked through each array handed to it in a serial fashion
> (as opposed to zip which walks the arrays in a parallel fashion).
Hmm... true enough. That was an aspect of the 'cat' function that I
hadn't been aware of. Rather, what came to mind when I saw the 'cat'
function was the following (from S29): "...a C<Cat> in item context
emulates the C<Str> interface lazily."
In short, 'cat("a" x 5)' effectively _is_ a scalar string value of
five characters - in item context. And because it emulates the string
interface _lazily_, there's no danger from an infinitely long string.
Again, I was not aware that there _was_ a distinct list context result
for 'cat'; and I'm pretty sure that it was referenced as an
alternative to '$a x *' due to its behavior in scalar context, rather
than its behavior in list context.
So the question is this: is there a problem with "'a' x 5" producing
"'a', 'a', 'a', 'a', 'a'" in list context, and 'aaaaa' in item
context? Or should it produce the latter in anything but void
context?
--
Jonathan "Dataweaver" Lang
I am almost certain that the following code is in list context.
pugs> my @a = '-' x 5, 'foo', '-' x 5;
pugs> @a
("-----", "foo", "-----")
pugs> my @b = cat('-' xx 5), 'foo', cat('-' xx 5)
("-", "-", "-", "-", "-", "foo", "-", "-", "-", "-", "-")
However, it does seem that Pug's version of cat does not handle the
Str emulation, so that may fix it, but I don't see how it could since
(at least in my mind) the code above is in list context.
