gforth-tutorial/fizz-buzz.fth

: true ( -- f ) -1 ;
: false ( -- f ) 0 ;

: div3? ( n -- f )
  dup 0=
  if
    true
  else
    dup 3 mod 0=
  then ;

: div5? ( n -- f )
  dup 0=
  if
    true
  else
    dup 5 mod 0=
  then ;

: fizz ( n -- n )
  div3?
  if ." fizz" then ;

: buzz ( n -- n )
  div5?
  if ." buzz" then ;

: fizzbuzz ( n -- )
  \ start with a -1 as counter
  -1
  \ 16 -1
  \ begin the loop
  begin
    \ increase counter, initially to 0
    1+
    \ 16 0
    dup . fizz buzz cr
    \ duplicate for `<=`
    2dup <=
  until
  2drop ;

100 fizzbuzz .s