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Postings from March 2001
On Mon, 19 Mar 2001 nick@ing-simmons.net wrote:
> Chris Stith <mischief@velma.motion.net> writes:
> >That is so if the examples are taken exactly as is. It is not so if
> >the example is put in the context of code following it. From which
> >match operator would the next line pull `$1'?
> >
> >Nick is talking about a body of code expecting something to be a
> >certain way when the code example above is executed.
>
> No I am not. (The example code is not mine and not a good example.
> It has && in it, is calling a builtin as a pseudo-sub and ...)
>
> I am talking about code that uses $1 in general, and with at least
^^^^^^^^
> a basic grasp of how the op tree is built. And with a background
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> in devious "lexing" schemes.
if( underlined_section_is_flame ) {
Thank you for assuming that because I'm not as intimately familiar
with perl or with your own explanation of this issue as are you
that I have no familiarity with lexing or parsing.
}
The thread, as quoted by Abigail, read to me as if you meant that
an existing body of code expected one or the other match on a single
line to become `$1'. I realized it was not your example, but the
context in which I was reading I understood to be proper context
for what you said. I must have misunderstood what point Abigail
was trying to make.
> Without a lot of flow analysis (that perl does not do) perl cannot tell
> that a particular use of $1 is (always) used in a way that means it should
> take a copy, or a way which means it should leave it "lazy".
>
> So my stance is that $1 is lazy, if you want/need a copy then write "$1".
That's something on which I am not prepared to comment, given that I
haven't studied that section of the interpreter thoroughly enough. The
only thing I will say is that if there's a way to do either the
programmer wishes, which you seem to say there is, then that should
be a definite plus compared to forcing `$1' itself one way or the other.
If `$1' is lazy now and can be forced to be a copy when wanted, then
that makes for the best flexibility.
> >A line of
> >code following the above example shouldn't expect one or the other
> >expression to be either `first' or `last', let alone expect which one
> >will be the value of `$1'.
>
> Things get less clear when you have something like:
>
> some_sub( (s/(0x([a-f0-9]+))/another_sub($1)/ie || s/(\d+)/third($1)/e) ? $1 : ... );
>
> In such cases "lazy" is what _I_ want for that last one at least and only
> by a lot of looking do you know which that is.
I notice you underline `I'. That's a good habit in a discussion such
as this. ;-)
Chris Stith