Does Perl combine multiple REs into a single automaton?

From: Clint Olsen (clint_at_0lsen.net)
Date: 06/28/04 

Date: Mon, 28 Jun 2004 17:04:23 GMT

Hi:

I posted earlier about how to speed up writing lexical analyzers in Perl.
With that effort in mind, I was curious to know if Perl combines multiple
patterns like:

if (/pat/) {
} elsif (/pat1/) {
...
} elsif (/pat2/) {
...
...
...
} else {
}

so that pat[\d]+ are in a sense combined via alternation with each branch
working like embedded action code?

The reason why I ask is that someone suggested I try to do this manually in
order to help speed up the pattern matching process (presumably using the
"(?{ code })" feature documented in perlre. Is it really faster to do it
this way?

When I'm in the debugger in Perl, I've noticed that the execution path gets
sort of muddied. I don't see Perl executing each match as a separate
statement. It's as if it jumps right to the code for the pattern match.
If that's the case, then there's not much of a compelling argument to embed
action code and cobmine REs.

Thanks,

-Clint

Relevant Pages

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