in reply to Need a regex to match C-style function arg list

Given the samples supplied, this does the trick. If your expressions can contain spaces, be split across lines or contain nested concats, then it will need further work. 

#! perl -slw
use strict;

my $re_term   = qr[[^,)]+?];
my $re_func   = qr[\w+\($re_term,$re_term\)];
my $re_concat = qr[concat\((?:($re_func),($re_term|$re_func))\)];

while(<DATA>) {
    s[^$re_concat$][$1 & $2];
    print;
}

__DATA__
concat(int2str(count,1),result)
concat(bit2str(count,'10'B),result)
concat(int2str(count,1),bit2str(count,'10'B))

[download]

Gives

c:\test>249976
int2str(count,1) & result

bit2str(count,'10'B) & result

int2str(count,1) & bit2str(count,'10'B)

[download]
Examine what is said, not who speaks.
1) When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
2) The only way of discovering the limits of the possible is to venture a little way past them into the impossible
3) Any sufficiently advanced technology is indistinguishable from magic.
Arthur C. Clarke.

In Section Seekers of Perl Wisdom