sub call_function {
   my $funcname = shift;
   my $package = caller();
   my $qfuncname = "${package}::$funcname";

   no strict 'refs';
   exists(&$qfuncname)
      or die("no such function $qfuncname\n");

   return &{$qfuncname}(@_);
}

sub f { print "f\n"; }

call_function('f');
call_function('g');