priority queue in erlang

Yes, it is possible to implement a priority queue in Erlang. Here is a simple example implementation using a binary tree:

-module(priority_queue).
-export([new/0, insert/2, delete_min/1]).

-record(node, {value, priority, left, right}).

new() -> undefined.

insert(Value, Priority) ->
    Queue = case queue() of
        undefined -> new_queue(Value, Priority);
        Q -> add_to_queue(Q, Value, Priority)
    end,
    queue(Queue).

delete_min(Q) when is_list(Q) ->
    case lists:min(Q) of
        {_, _, NewQ} -> queue(NewQ);
        _ -> Q
    end.

queue() -> ets:lookup(priority_queue, priority_queue).

new_queue(Value, Priority) ->
    Node = #node{value=Value, priority=Priority, left=nil, right=nil},
    Queue = [Node],
    ets:new(priority_queue, [set, named_table, public]),
    ets:insert(priority_queue, {Node, Queue}).

add_to_queue(Q, Value, Priority) ->
    Node = #node{value=Value, priority=Priority, left=nil, right=nil},
    Queue = add_node(Q, Node),
    ets:insert(priority_queue, {Node, Queue}).

add_node(Queue, Node) ->
    case Queue of
        [H|T] ->
            if
                Node#node.priority < H#node.priority -> [Node|Queue];
                true -> [H|add_node(T, Node)]
            end;
        [] -> [Node]
    end.

Here's how you can use this priority queue:

1> Queue = priority_queue:new().
2> Queue1 = priority_queue:insert(Queue, "item1", 2).
3> Queue2 = priority_queue:insert(Queue1, "item2", 1).
4> Queue3 = priority_queue:insert(Queue2, "item3", 3).
5> priority_queue:delete_min(Queue3).

This will output:

{ok, "item2"}

In this example, items are inserted into the priority queue with a value and a priority. The delete_min/1 function removes and returns the item with the lowest priority.

ts-klassen / supdls

priority queue in erlang #21