REBOL [
    Title: "Cheasy (Cheap-n-Easy) Priority Queue"
]

pq-insert: func [
    list [any-block!]   "The queue"
    item
    priority [integer!]
][
    sort/skip/reverse append list reduce [priority item] 2
]

pq-remove: func [
    "Remove an item from the priority queue"
    list [any-block!]   "The queue"
    /index  "Remove a specific item"
        idx [integer!] "The specific item to remove"
][
    remove/part either index [at list (idx * 2 - 1)][head list] 2
]

pq-first: func [
    list [any-block!]   "The queue"
][
    ; skip over the priority value and return the actual value
    ; that was inserted in the queue.
    first next head list
]

priority-queue: make object! [
    data: copy []

    insert: func [item priority] [pq-insert data item priority]

    remove: func [/index idx] [
        either index [pq-remove/index data idx][pq-remove data]
    ]

    first: does [pq-first data]
]



pq: copy []
print pq-insert pq "A" 1
print pq-insert pq "B" 10
print pq-insert pq "C" 100
print pq-insert pq "D" 1000
print pq-remove/index pq 3
print pq-remove pq
print mold pq
print pq-insert pq "CC" 100
print pq-insert pq "CCC" 100
print pq-insert pq "D" 1000
print pq-insert pq "CCCC" 100
print pq-insert pq "CCCCC" 100
print pq-remove pq
print pq-insert pq "CCCCCC" 100
print pq-insert pq "CCCCCCC" 100

print ""

pq: make priority-queue []
print pq/insert"A" 1
print pq/insert"B" 10
print pq/insert"C" 100
print pq/insert"D" 1000
print pq/remove/index 3
print pq/remove ;pq
print mold pq/data
print pq/insert"CC" 100
print pq/insert"CCC" 100
print pq/insert"D" 1000
print pq/insert"CCCC" 100
print pq/insert"CCCCC" 100
print pq/remove ;pq/data
print pq/insert"CCCCCC" 100
print pq/insert"CCCCCCC" 100


halt