fun do-op a b op {
    match op
    with '+: a + b
    with '-: a - b
    with '*: a * b
    with '/: a / b
    with  _: error
}

flow gen a b ops -> res {
    (do-op a>> b>> ops>>) -> >>res
}

do main {
    commit (reduce print
                   (gen [1 2 3]
                        [3 2 1]
                        ['+ '- '*]))
}