You can think of any regular expression in term of some nested for loops.
Please, consider:
for my $i (0 .. $eos) {
for my $j ($min .. $max) {
last if $j > $eos-$i;
print substr($str, $i, $j),"\n";
}
}
The following variables specifies the meaning of "ABCDEF" =~ /(\w{2,}?)(?{print "$1\n"})(?!)/;
my $min = 2; # minimum match length
my $max = 32767; # maximum match length
my $str = "ABCDEF";
my $eos = length($str);
Using the same nested for loops, we have another specification for "ABCDEF" =~ /([A-Z]{3})(?{print "$1\n"})(?!)/;
my $min = 3; # minimum match length
my $max = 3; # maximum match length
my $str = "ABCDEF";
my $eos = length($str);
By executing the code, it gives us the same output as the corresponding regular expressions do. I hope this will give you a basic intuition on how backtracking works.
-
Are you posting in the right place? Check out Where do I post X? to know for sure.
-
Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big>
<blockquote> <br /> <dd>
<dl> <dt> <em> <font>
<h1> <h2> <h3> <h4>
<h5> <h6> <hr /> <i>
<li> <nbsp> <ol> <p>
<small> <strike> <strong>
<sub> <sup> <table>
<td> <th> <tr> <tt>
<u> <ul>
-
Snippets of code should be wrapped in
<code> tags not
<pre> tags. In fact, <pre>
tags should generally be avoided. If they must
be used, extreme care should be
taken to ensure that their contents do not
have long lines (<70 chars), in order to prevent
horizontal scrolling (and possible janitor
intervention).
-
Want more info? How to link
or How to display code and escape characters
are good places to start.
|