1 files changed, 89 insertions, 0 deletions
diff --git a/src/lqueue.erl b/src/lqueue.erl
new file mode 100644
index 0000000000..4a8164f6db
--- /dev/null
+++ b/src/lqueue.erl
@@ -0,0 +1,89 @@
+%% The contents of this file are subject to the Mozilla Public License
+%% Version 1.1 (the "License"); you may not use this file except in
+%% compliance with the License. You may obtain a copy of the License
+%% at http://www.mozilla.org/MPL/
+%%
+%% Software distributed under the License is distributed on an "AS IS"
+%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+%% the License for the specific language governing rights and
+%% limitations under the License.
+%%
+%% The Original Code is RabbitMQ.
+%%
+%% The Initial Developer of the Original Code is VMware, Inc.
+%% Copyright (c) 2011-2011 VMware, Inc.  All rights reserved.
+%%
+
+-module(lqueue).
+
+-export([new/0, is_empty/1, len/1, in/2, in_r/2, out/1, out_r/1, join/2,
+         foldl/3, foldr/3, from_list/1, to_list/1]).
+
+-define(QUEUE, queue).
+
+-ifdef(use_specs).
+
+-export_type([?MODULE/0]).
+
+-opaque(?MODULE() :: {non_neg_integer(), ?MODULE()}).
+-type(value() :: any()).
+-type(result() :: ({'empty', ?MODULE()} |
+                   {{'value', value()}, ?MODULE()})).
+
+-spec(new/0 :: () -> ?MODULE()).
+-spec(is_empty/1 :: (?MODULE()) -> boolean()).
+-spec(len/1 :: (?MODULE()) -> non_neg_integer()).
+-spec(in/2 :: (value(), ?MODULE()) -> ?MODULE()).
+-spec(in_r/2 :: (value(), ?MODULE()) -> ?MODULE()).
+-spec(out/1 :: (?MODULE()) -> result()).
+-spec(out_r/1 :: (?MODULE()) -> result()).
+-spec(join/2 :: (?MODULE(), ?MODULE()) -> ?MODULE()).
+-spec(foldl/3 :: (fun ((value(), B) -> B), B, ?MODULE()) -> B).
+-spec(foldr/3 :: (fun ((value(), B) -> B), B, ?MODULE()) -> B).
+-spec(from_list/1 :: ([value()]) -> ?MODULE()).
+-spec(to_list/1 :: (?MODULE()) -> [value()]).
+
+-endif.
+
+new() -> {0, ?QUEUE:new()}.
+
+is_empty({0, _Q}) -> true;
+is_empty(_)       -> false.
+
+in(V, {L, Q}) -> {L+1, ?QUEUE:in(V, Q)}.
+
+in_r(V, {L, Q}) -> {L+1, ?QUEUE:in_r(V, Q)}.
+
+out({0, _Q} = Q) ->
+    {empty, Q};
+out({L, Q}) ->
+    {Result, Q1} = ?QUEUE:out(Q),
+    {Result, {L-1, Q1}}.
+
+out_r({0, _Q} = Q) ->
+    {empty, Q};
+out_r({L, Q}) ->
+    {Result, Q1} = ?QUEUE:out_r(Q),
+    {Result, {L-1, Q1}}.
+
+join({L1, Q1}, {L2, Q2}) ->
+    {L1 + L2, ?QUEUE:join(Q1, Q2)}.
+
+to_list({_L, Q}) -> ?QUEUE:to_list(Q).
+
+from_list(L) -> {length(L), ?QUEUE:from_list(L)}.
+
+foldl(Fun, Init, Q) ->
+    case out(Q) of
+        {empty, _Q}      -> Init;
+        {{value, V}, Q1} -> foldl(Fun, Fun(V, Init), Q1)
+    end.
+
+foldr(Fun, Init, Q) ->
+    case out_r(Q) of
+        {empty, _Q}      -> Init;
+        {{value, V}, Q1} -> foldr(Fun, Fun(V, Init), Q1)
+    end.
+
+len({L, _Q}) ->
+    L.