Why aren't Perl's patterns regular expressions?
Q
Why aren't Perl's patterns regular expressions?
✍: Guest
A
Because Perl patterns have backreferences.
A regular expression by definition must be
able to determine the next state in the finite
automaton without requiring any extra memory
to keep around previous state. A pattern /([ab]+)c\1/
requires the state machine to remember old
states, and thus disqualifies such patterns
as being regular expressions in the classic sense
of the term.
2013-09-02, 2040👍, 0💬
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