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From: Andrew.Vignaux@comp.vuw.ac.nz (Andrew Vignaux)
Newsgroups: comp.lang.perl
Subject: Re: Perl Neophyte Needs Help
Message-ID: <1990Jun27.101219.11357@comp.vuw.ac.nz>
Date: 27 Jun 90 10:12:19 GMT
References: <HOGAN.90Jun26123510@trollope.csl.sri.com> <8504@jpl-devvax.JPL.NASA.GOV>
Sender: news@comp.vuw.ac.nz (News Admin)
Organization: Comp Sci, Victoria University, Wellington, New Zealand.
Lines: 45

In article <8504@jpl-devvax.JPL.NASA.GOV>, lwall@jpl-devvax.JPL.NASA.GOV
(Larry Wall) writes:
> The only other tricky thing we might do here is to put the whole loop
> inside an eval so that the pattern gets compiled before the optimizer
> runs.  The eval is just using the here-is syntax to quote the evaluated
> bit of program.
> [...]
> $pattern = shift;	# get first argument
> [...]
> eval <<"EOF";		# to avoid recompile pattern each time
>     while (<>) {
> 	print if /$pattern/;
>     }
> EOF

I've always been a little wary about using the "eval-the-loop" trick
because it will probably mean that the whole perl compiler/interpreter
will get sucked into my executable when (not if :-) a "perl to C
translator" comes along.  [Note: ispell thinks that "eval" is "evil"
-- so it's not just my opinion :-]

Of course this doesn't stop me using it.

I think the only time *I* every really want to do this is for building
the regexp test(s) based on the script arguments i.e. a grep-like
script (just like this example).  Does/could perl notice that $pattern
is invariant in the original program and arrange to compile the regexp
only once?

Comments?

Andrew
-- 
Domain address: Andrew.Vignaux@comp.vuw.ac.nz

PS: While I was looking at the Wishlist, I noticed that "built-in cpp"
    was there.  Well, I'd be really keen on at least "#include".  I've
    also been worried about the distinction between "#include" and
    "do".  I often want to include a subroutine in multiple scripts:
    I'd rather not have the longer cpp startup time when I'm
    interpreting the script, or the runtime compile of "do" for the
    compiled script.
    Should I be using the pat.SH / package.pl (from dist) approach?

PPS: ispell suggests that "perl" is "peril", but we already knew that :-)