prioq.hny

import lists

def set_at(xs, i, v) returns ys:
    ys = lists.subseq(xs, 0, i) + [v,] + lists.subseq(xs, i + 1, len(xs))

def PrioQ(n) returns init:
    init = { .n: n, .tails: [[] for _ in {0..n-1}] }

def put(pq, prio, v):
    atomically:
        let q = !pq:
            let tails = q["tails"]:
                let updated = lists.append(tails[prio], v):
                    !pq = { .n: q["n"], .tails: set_at(tails, prio, updated) }

def get(pq) returns r:
    atomically:
        let q = !pq:
            var p = 0
            while (p < q["n"]) and (q["tails"][p] == []):
                p += 1

            if p == q["n"]:
                r = (False, None)
            else:
                let tails = q["tails"]:
                    let priolist = tails[p]:
                        r = (True, lists.head(priolist))
                        !pq = { .n: q["n"], .tails: set_at(tails, p, lists.tail(priolist)) }