--- Rob Dixon <[EMAIL PROTECTED]> wrote:
> Sam wrote:
> >
> > Thanks for all your responses; I learned a bit.
>
> Good: well done.
>
> > 1. I wasn't clear on $_ in my email; that's being read elsewhere in
> program so
> > it's already set by the time print_lines is called.
>
> You /mustn't/ use $_ like that. It's meant to be an 'it' in places like
What? You want me to pass the line around in a variable! :-)
>
> For each banana, look at it, smell it, and eat it.
>
> NOT
>
> When I say 'it', it means 'banana 3 from crate 5'.
> For each apple, look at it, smell it, and eat it.
> Do it to it.
>
> > 2. Will you bet your life on this equivalence: "not /^\s*$/ == /\S/"? I
> > believe it's safer to negate an EXPR than to find some other EXPR2 that is
> > equivalent to 'not EXPR'.
>
> Yes. (But I can think of more valuable things to bet on.)
>
> The first says,
>
> Does the entire string, from start to end, consist of zero or more 'space'
> characters?
>
> The second says,
>
> Does the string contain a non-'space' character anywhere?
>
> The only difficulty could be with a zero-length string, which is still fine,
> if
> you think about it.
I hear 'ya, but I like to avoid possible boundary conditions that make me think
'what if.' Just using 'not' avoids that mess. In this case the re was simple
enough, but w/more complex ones...
>
> > 3. Hadn't thought about xor; good to know.
>
> Be careful though. 'xor' goes with the other low-precedence operators 'and'
> and 'or', which have the high-precedence equivalents && and ||. 'xor' has
> no equivalent. (The caret, ^, is a bitwise operator, which is completely
> different.)
>
> > 4. As for the generalized case, I learned about using refs. Anonymous
> subs
> > also work.
> >
> > my $re = sub { return /^\s*$/; };
> > my $nre = sub { return not &$re; };
>
> Eek. Don't do that. It may work, but it's not at all obvious what $_ is in
> the
> context of a subroutine call. Having $nre dereference $re at each call isn't
> your best bet either.
>
> > my $expr = $blank ? $re : $nre;
> > do ... while (&$expr and not eof);
>
> The better syntax for a call to a subroutine reference is
>
> $expr->()
>
> which doesn't assume all sorts of things that could keep you awake at night
> if
> you knew.
Ok, that's good to know.
>
> > But I'm not sure which is faster though.
>
> If you don't know, it doesn't matter.
>
> If your software is /too/ slow and you would die for a 10% speed increase
> then
> check out
>
> use Benchmark;
>
> If not, don't bother.
No it hums along fine. But using eval was *really* slow and clearly I was on
the wrong track using it.
Thanks.
>
> HTH,
>
> Rob
>
>
>
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