Please help me out with syntax mistakes

fun rappend(L1,L2)
    if null L2 then L1
    else rappend(tl(L2) @ L1, hd(L2))

figured it out. Stupid syntax :(.

Here's the answer

rappend(L1,L2)
    if null L2 then L1
    else rappend(tl(L2)@L1,[hd(L2)])

darn I can't seem to figure out how to do reverse append.