[schsafe]

If you want to play with an online FORTH interpreter:

http://forthfreak.net/jsforth80x25.html

  ok

: fibo 1 dup 45 0 do . dup rot rot + dup loop ;

  ok

fibo

1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181 6765 10946 17711 2 8657 46368 75025 121393 196418 317811 514229 832040 1346269 2178309 3524578 5702 887 9227465 14930352 24157817 39088169 63245986 102334155 165580141 267914296 43 3494437 701408733 1134903170 ok..

The Fibonacci numbers :-)