While trying to write a simple Scheme parser in PHP, we encountered this problem:

In perl, you can capture the delimiters passed to split() by enclosing the portion with brackets, in the regexp.  This does not work in PHP.

For example, here is the perl script, and its output:

#!/usr/bin/perl
use Data::Dumper;

$_ = '(define heshe (if (equal gender "Male") "He" "She")) ';
@b = split /([\(\)])/;
print Dumper(@b);

Output:
$VAR1 = '';
$VAR2 = '(';
$VAR3 = 'define heshe ';
$VAR4 = '(';
$VAR5 = 'if ';
$VAR6 = '(';
$VAR7 = 'equal gender "Male"';
$VAR8 = ')';
$VAR9 = ' "He" "She"';
$VAR10 = ')';
$VAR11 = '';
$VAR12 = ')';
$VAR13 = ' ';

But in PHP:

<? $a = '(define heshe (if (equal gender "Male") "He" "She")) ';
$b = preg_split('/([\(\)])/', $a);
var_dump($b); ?>

Outputs:
array(7) {
  [0]=>
  string(0) ""
  [1]=>
  string(13) "define heshe "
  [2]=>
  string(3) "if "
  [3]=>
  string(19) "equal gender "Male""
  [4]=>
  string(11) " "He" "She""
  [5]=>
  string(0) ""
  [6]=>
  string(1) " "
}

The brackets aren't captured, which makes the Scheme parsing a bit difficult :-)  There are other ways to do this, of course, but the preg_split() would be the simplest and the most efficient way to do it, as far as we can see.

I noticed that the PCRE libraries are only at version 3.0 in PHP, and that 3.4 is available from the main site.  I'll try updating to that, and see if it solves this.