Re: [9fans] non greedy regular expressions

["Russ Cox" <rsc@swtch.com>]

Regarding greedy vs non-greedy etc.

In Plan 9, a regular expression search always looks
for the "leftmost-longest" match, which means
a match that starts as far to the left as possible
in the target text, and of the matches that start there,
the longest one.

In that model, it is not accurate to describe the * + ?
operators as greedy or not.  None of them is working
toward any goal other than the overall longest match
at the leftmost position.

In Perl and its imitators, the match starts at the leftmost
position but is otherwise the first one that is found,
not necessarily the longest.  In that context, words like
"greedy" and "non-greedy" start to make sense,
because the behavior of any one operator influences which
match is encountered first.

Either approach -- leftmost-longest or leftmost-first --
can be implemented using finite automata.

Russ