$np = qr{
\(
(?:
(?> [^()]+ ) # Non–parens without backtracking
|
(??{ $np }) # Group with matching parens
)*
\)
}x;

##</code><code>##

$funpat = qr/\w+$np/;<br>
"myfunfun(1,(2*(3+4)),5)" =~ /^$funpat$/; #Matches!"