Hello Monks,

I have some doubts about RegEx engine in Perl. The thing is, i know that there are fundamentally 2 RegEx engine NFA and DFA. The source of my info is in below link, i hope its not obsolete yet: master regular expression pdf - Chapter 4. So according to that, Perl is based on NFA engine. But when i check below matching: 

$_ = "The first recorded efforts to reach Everest's summit were made b
+y British mountaineers    ";
/summit|Everest|mountain/;
print $&;  #Result is "Everest"

[download]

For NFA the engine will move the control over the RegEx, encounter with the alternation, the engine will check it in turn, so "summit" is checked first and matched. At this point overall match is achieved and the engine should stop but no. The result is most likely from the DFA engine as it will move the control over the target text. First the engine will look into the target string "The first ....", since it find the "Everest" first and the RegEx satisfies that -> Overall match achived! Even if the engine will choose the leftmost match. Then "summit" should be evaluated once? So I try to use a second approach: 

$_ = "The first recorded efforts to reach Everest's summit were made b
+y British mountaineers    ";
/summit(?{print "11"})|Everest(?{print "22"})|mountain(?{print "33"})/
+;
print $&;  #22Everest

[download]

The result shows that "summit" is not evaluated! Did i misunderstand something here about the "alteration" or about the RegEx engine? Or Perl is not NFA anymore but Hybrid NFA + DFA? Dear Monks, please enlighten me.

Thanks in advance!

In reply to Is RegEx in Perl not NFA anymore? by redbull2012

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