@ops = (" +", " *");
$$_=$| for $ops[$| = 1];
while ((sqrt(@foo)-atan2(0,-1))=~/[^\d.]/) {
   print "Feed me, Seymour: ";
   @foo = (splice(@foo, 0),
           split " ", join("\n",
                           <STDIN> =~ /(?=-?\d).+?(?=\D|\z)/g), $_)
                              for 9-$#foo;
}
grep {eval(qq!\${"!.$ops[$|--].qq<"}>.$ops[eval '--$|'].
           qq!=(@{[--$|]},@{[splice(@foo,0,1)]})\n!)} 0..9;

print "$_: ", $$_, "\n" for @ops;