This is the second part of a series of educational regex articles. It shows how lookaheads and nested references can be used to match the non-regular languge anbn. Nested references are first introduced in: How does this regex find triangular…
Part of a series of educational regex articles, this is a gentle introduction to the concept of nested references.
The first few triangular numbers are:
1 = 1
3 = 1 + 2
6 = 1 + 2 + 3
10 = 1 + 2 + 3 + 4
15 = 1 + 2 + 3 + 4 + 5
There are many…
This is the third part in a series of educational regex articles. It follows How does this regex find triangular numbers? (where nested references is first introduced) and How can we match a^n b^n with Java regex?
(where the lookahead "counting"…
This question is an educational demonstration of the usage of lookahead, nested reference, and conditionals in a PCRE pattern to match ALL palindromes, including the ones that can't be matched by the recursive pattern given in the PCRE man…
This is the fourth part in a series of educational regex articles. It show how the combination of nested reference (see: How does this regex find triangular numbers?) to "count" within assertions (see: How can we match a^n b^n with Java regex?) can…
I've written a regex pattern to find Fibonacci numbers (it doesn't matter why, I just did). It works wonderfully as expected (see on ideone.com):
String FIBONACCI =
"(?x) .{0,2} | (?: (?=(\\2?)) (?=(\\2\\3|^.)) (?=(\\1)) \\2)++ . ";
…
This is an experimental new feature for StackOverlow: exercising your regex muscles by solving various classical problems. There is no one right answer, and in fact we should collect as many right answers as possible, as long as they offer…
As a follow up to my previous post here!
I tested the algorithm with nested hash references:
Algorithm:
use strict;
use warnings;
&expand_references2([a,b,{c=>123},d]);
sub expand_references2 {
my $indenting = -1;
my $inner; $inner = sub {
…
