$_ = "sin(atan2(sin(1),cos(1))),atan2(1,1),cos(atan2(sin(2),cos(2)))\n";
(my $re=$_)=~s/((\()|(\))|.)/${[')','']}[!$3]\Q$1\E${['(','']}[!$2]/gs;
$re= join'|',map{quotemeta}eval{/$re/};
die $@ if $@ =~ /unmatched/;
print while s/(\w+\(($re)\))/$1/ee;