$text = "A(B(2)+C(D())),\nTT(TT()+TT(TT()))";
$text = doFunc( "MAIN", $text );  #
print "Example: $text\n";

sub doFunc{
   my( $theFunc, $theParam ) = @_;

   # FIXME: greedy match fails with: 'TT(TT()+TT(TT()))'
   my $re;
   {local $^W=0; ($re=$theParam)=~s/((\()|(\))|.)/${[')']}[!$3]\Q$1\E$
+{['(']}[!$2]/gs;
   $re= join'|',map{quotemeta}eval{$theParam=~/$re/};}
   die $@ if $@=~/unmatched/;

   $theParam =~ s/([A-Z]+)\(($re)\)/&doFunc($1,$2)/geo;

   my $result = "";

   if( $theFunc eq "MAIN" ) {
     $result = $theParam;

   } else {
     # dummy switch here for demonstration
     # this would be an elsif for each function
     $result = "func $theFunc returns <$theParam>";

   }

   return $result;
}
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