(
    ; using a coroutine as a generator

    (spawn r15 fibo)

    (ld r0 20)
    (:next)

    (ld r1 @r15) ; Read a yielded value
    (call printnum r1)
    (lds @cout ", ")

    (dec r0)
    (j.nz :next)
    (ld @cout '\n')
    (halt)

    (proc fibo
        (ld r0 0)
        (ld r1 1)
        (:x)
        (yield r1)
        (add r2 r0 r1)
        (ld r0 r1)
        (ld r1 r2)
        (j :x)
    )

    (proc printnum num
        (mkbf r15)
        (ld r1 num)
        (tst r1 (<0? (mul r1 -1)))
        (:next)
            (mod r0 r1 10)
            (add r0 '0')
            (bfrpush @r15 r0)
            (div r1 10 (z?
                (tst num (<0? (bfrpush @r15 '-')))
                (lds @cout @r15)
                (del @r15)
                (ret)))
            (j :next)
    )
)