( scratchpad ) : fib-count ( a b -- x y ) [ dup 4000000 <= ] [ [ + ] keep swap ] while ;
( scratchpad ) 0

--- Data stack:
0
( scratchpad ) 1

--- Data stack:
0
1
( scratchpad ) fib-count

--- Data stack:
3524578
5702887
( scratchpad ) clear
( scratchpad ) : fib-count2 ( -- x y ) 0 1 [ dup 4000000 <= ] [ [ + ] keep swap ] while ;
( scratchpad ) fib-count2

--- Data stack:
3524578
5702887
( scratchpad )