define decrement
  dup $decrement_var !
  @ 1 - $decrement_var @ !
  $decrement_var forget ;

10 $idx !
[ $idx @ dup 0 gt? ]            -- while idx > 0
    [ 2 mod 0 eq?               -- print "even" if even, "odd" if odd
        [ "even" s. ]
        [ "odd" s. ] cond
      $idx decrement ] loop     -- decrement idx by 1
drop