( Increase loop counter and returns whether we should loop. )
: _
    R>          ( IP, keep for later )
    R> 1+       ( ip i+1 )
    DUP >R      ( ip i )
    I' =        ( ip f )
    SWAP >R     ( f )
;
( One could think that we should have a sub word to avoid all
  these COMPILE, but we can't because otherwise it messes with
  the RS )
: LOOP
    COMPILE _ COMPILE (?br)
    H@ - ,
    COMPILE R> COMPILE DROP COMPILE R> COMPILE DROP
; IMMEDIATE