diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..137b8fb
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,18 @@
+name: "ci"
+
+on: [push, pull_request]
+
+jobs:
+  ci:
+    name: "ci"
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2.3.4
+    - uses: cachix/install-nix-action@v13
+      with:
+        nix_path: nixpkgs=channel:nixos-21.05
+    - uses: cachix/cachix-action@v10
+      with:
+        name: ninegua
+        authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+    - run: nix-shell --run 'make -C test'
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..e29584c
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2022 Paul Liu
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..b28d671
--- /dev/null
+++ b/README.md
@@ -0,0 +1,20 @@
+# Mutable Queue
+
+A [motoko] module of a mutable queue data structure supporting both `pushFront` and `pushBack` but only `popFront`.
+It can be conveniently used for stable variables to hold a collection of values if you don't mind O(n) lookups.
+
+Internally it is just a linked list with both `first` and `last` pointers.
+
+You can use this library with the [vessel] package manager.
+
+## Development
+
+Documentation is non-existent but functions should be self-explanatory given their types.
+
+If you have installed a [nix] environment, you can run the tests like this:
+
+```
+nix-shell
+cd test
+make
+```
diff --git a/package-set.dhall b/package-set.dhall
new file mode 100644
index 0000000..0082e15
--- /dev/null
+++ b/package-set.dhall
@@ -0,0 +1 @@
+https://github.com/dfinity/vessel-package-set/releases/download/mo-0.6.18-20220107/package-set.dhall
diff --git a/shell.nix b/shell.nix
new file mode 100644
index 0000000..16118fb
--- /dev/null
+++ b/shell.nix
@@ -0,0 +1,8 @@
+{ pkgs ? import <nixpkgs> {} }:
+let
+  ic-utils = import (builtins.fetchGit {
+    url = "https://github.com/ninegua/ic-utils";
+    rev = "6e9b645e667fb59f51ad8cfa40e2fd7fdd7e52d0";
+    ref = "refs/heads/main";
+  }) { inherit pkgs; };
+in pkgs.mkShell { nativeBuildInputs = [ ic-utils pkgs.wasmtime ]; }
diff --git a/src/Queue.mo b/src/Queue.mo
new file mode 100644
index 0000000..42df7d1
--- /dev/null
+++ b/src/Queue.mo
@@ -0,0 +1,323 @@
+/*
+ * A mutable queue with pushFront and pushBack, but only popFront.
+ *
+ */
+import Iter "mo:base/Iter";
+import Nat64 "mo:base/Nat64";
+import Option "mo:base/Option";
+
+import Matchers "mo:matchers/Matchers";
+import T "mo:matchers/Testable";
+import Suite "mo:matchers/Suite";
+
+module Queue {
+  public type List<T> = {
+    item: T;
+    var next: ?List<T>;
+  };
+
+  public type Queue<T> = {
+    var size: Nat64;
+    var first: ?List<T>;
+    var last: ?List<T>;
+  };
+
+  public func empty<T>() : Queue<T> {
+    { var size = 0; var first = null; var last = null; }
+  };
+
+  public func pushBack<T>(q: Queue<T>, item: T) : Queue<T> {
+    let list : List<T> = { item = item; var next = null };
+    switch (q.first, q.last) {
+      case (?first, ?last) {
+        last.next := ?list;
+        q.last := last.next;
+      };
+      case (_, _) {
+        q.first := ?list;
+        q.last := q.first;
+      }
+    };
+    q.size := q.size + 1;
+    q
+  };
+
+  public func pushFront<T>(item: T, q: Queue<T>) : Queue<T> {
+    let list : List<T> = { item = item; var next = null };
+    switch (q.first, q.last) {
+      case (?first, ?last) {
+        list.next := ?first;
+        q.first := ?list;
+      };
+      case (_, _) {
+        q.first := ?list;
+        q.last := q.first;
+      }
+    };
+    q.size := q.size + 1;
+    q
+  };
+
+  public func popFront<T>(q: Queue<T>) : ?T {
+    switch (q.first, q.last) {
+      case (?first, ?last) {
+        q.size := q.size - 1;
+        let item = first.item;
+        if (q.size == 0) {
+          q.first := null;
+          q.last := null;
+        } else {
+          q.first := first.next;
+        };
+        ?item
+      };
+      case (_, _) null;
+    }
+  };
+
+  public func rotate<T>(q: Queue<T>) : Queue<T> {
+    switch (q.first, q.last) {
+      case (?first, ?last) {
+        if (q.size > 1) {
+          q.first := first.next;
+          first.next := null;
+          last.next := ?first;
+          q.last := last.next;
+        }
+      };
+      case (_, _) ();
+    };
+    q
+  };
+
+  public func remove<T>(q: Queue<T>, eq: T -> Bool) : Queue<T> {
+    ignore removeOne(q, eq);
+    q
+  };
+
+  public func removeOne<T>(q: Queue<T>, eq: T -> Bool) : ?T {
+    switch (q.first, q.last) {
+      case (?first, ?last) {
+        if (eq(first.item)) {
+          q.first := first.next;
+          if (Option.isNull(q.first)) {
+            q.last := null;
+          };
+          q.size := q.size - 1;
+          ?first.item;
+        } else {
+          var prev = first;
+          label L loop {
+            switch (prev.next) {
+              case null { break L };
+              case (?next) {
+                if (eq(next.item)) {
+                  prev.next := next.next;
+                  if (Option.isNull(prev.next)) {
+                    q.last := ?prev;
+                  };
+                  q.size := q.size - 1;
+                  return ?next.item;
+                };
+                prev := next;
+              }
+            }
+          };
+          null
+        }
+      };
+      case _ { null };
+    }
+  };
+
+  public func first<T>(q: Queue<T>) : ?T {
+    Option.map(q.first, func (x: List<T>) : T { x.item })
+  };
+
+  public func last<T>(q: Queue<T>) : ?T {
+    Option.map(q.last, func (x: List<T>) : T { x.item })
+  };
+
+  public func make<T>(item: T) : Queue<T> {
+    let q = empty<T>();
+    pushBack<T>(q, item)
+  };
+
+  public func size<T>(q: Queue<T>) : Nat {
+    Nat64.toNat(q.size)
+  };
+
+  public func toIter<T>(q: Queue<T>) : Iter.Iter<T> {
+    var cursor = q.first;
+    func next() : ?T {
+      switch (cursor) {
+        case null null;
+        case (?list) {
+          let item = list.item;
+          cursor := list.next;
+          ?item
+        }
+      }
+    };
+    { next = next }
+  };
+
+  public func find<T>(q: Queue<T>, f: T -> Bool) : ?T {
+    for (item in toIter(q)) {
+      if (f(item)) { return ?item }
+    };
+    null
+  };
+
+  public func fold<T, V>(q: Queue<T>, init: V, acc: (V, T) -> V) : V {
+    var sum = init;
+    for (item in toIter(q)) {
+      sum := acc(sum, item);
+    };
+    sum
+  };
+
+  public func fromIter<T>(iter: Iter.Iter<T>) : Queue<T> {
+    let q = empty<T>();
+    for (item in iter) {
+      ignore pushBack(q, item);
+    };
+    q
+  };
+
+  public func fromArray<T>(arr: [T]) : Queue<T> {
+    fromIter(Iter.fromArray(arr))
+  };
+
+  public func toArray<T>(q: Queue<T>) : [T] {
+    Iter.toArray<T>(toIter(q))
+  };
+
+  public func map<A, B>(inp: Queue<A>, f: A -> B) : Queue<B> {
+    let out = Queue.empty<B>();
+    for (x in toIter(inp)) {
+      ignore pushBack(out, f(x));
+    };
+    out
+  };
+
+  type Suite = Suite.Suite;
+  public func test() : Suite {
+    func wellformed<A>(q: Queue<A>) : Queue<A> {
+      switch (q.first, q.last) {
+        case (?first, ?last) {
+          assert(size(q) > 0);
+          if (size(q) == 1) {
+            assert(Option.isNull(first.next));
+            assert(Option.isNull(last.next));
+          } else {
+            var n = 0;
+            var p = first;
+            label L loop {
+              n := n + 1;
+              switch (p.next) {
+                case null { break L };
+                case (?next) { p := next; }
+              }
+            };
+            assert(n == size(q));
+          }
+        };
+        case (?_, _) { assert(false) };
+        case (_, ?_) { assert(false) };
+        case (_, _)  { assert(size(q) == 0) };
+      };
+      q
+    };
+
+    func toArray_<A>(q: Queue<A>) : [A] {
+      toArray(wellformed(q))
+    };
+
+    let to_array_test =
+      Suite.suite("toArray", [
+        Suite.test("empty",
+          toArray_(empty<Nat>()),
+          Matchers.equals(T.array<Nat>(T.natTestable, []))),
+        Suite.test("singleton",
+          toArray_(make<Nat>(1)),
+          Matchers.equals(T.array<Nat>(T.natTestable, [1]))),
+        Suite.test("multiple",
+          toArray_(pushFront(0, pushBack(make<Nat>(1), 2))),
+          Matchers.equals(T.array<Nat>(T.natTestable, [0, 1, 2]))),
+    ]);
+
+    let size_test =
+      Suite.suite("size", [
+        Suite.test("empty",
+          size(empty<Nat>()),
+          Matchers.equals(T.nat(0))),
+        Suite.test("singleton",
+          size(make<Nat>(1)),
+          Matchers.equals(T.nat(1))),
+        Suite.test("multiple",
+          size(pushFront(0, pushBack(make<Nat>(1), 2))),
+          Matchers.equals(T.nat(3))),
+        Suite.test("fromArray",
+          size(fromArray<Nat>([1,2,3,4])),
+          Matchers.equals(T.nat(4))),
+        Suite.test("popFront",
+          size(do { let q = make<Nat>(1); ignore popFront(q); q }),
+          Matchers.equals(T.nat(0))),
+        Suite.test("pushFront",
+          size(pushFront(0, make<Nat>(1))),
+          Matchers.equals(T.nat(2))),
+        Suite.test("pushBack",
+          size(pushBack(make<Nat>(1), 2)),
+          Matchers.equals(T.nat(2))),
+        Suite.test("rotate",
+          size(rotate(fromArray<Nat>([1,2,3,4]))),
+          Matchers.equals(T.nat(4))),
+    ]);
+
+    func eq(a: Nat) : Nat -> Bool { func (b: Nat) : Bool { a == b } };
+    let removal_test =
+      Suite.suite("removal", [
+        Suite.test("removeOne/empty",
+          removeOne<Nat>(empty<Nat>(), eq(10)),
+          Matchers.equals(T.optional<Nat>(T.natTestable, null))),
+        Suite.test("removeOne/one",
+          removeOne<Nat>(make<Nat>(10), eq(10)),
+          Matchers.equals(T.optional(T.natTestable, ?10))),
+        Suite.test("removeOne/one_1",
+          removeOne<Nat>(make<Nat>(0), eq(10)),
+          Matchers.equals(T.optional<Nat>(T.natTestable, null))),
+        Suite.test("removeOne/two",
+          removeOne<Nat>(fromArray<Nat>([3,10]), eq(3)),
+          Matchers.equals(T.optional(T.natTestable, ?3))),
+        Suite.test("removeOne/two_1",
+          removeOne<Nat>(fromArray<Nat>([3,10]), eq(10)),
+          Matchers.equals(T.optional(T.natTestable, ?10))),
+        Suite.test("removeOne/two_2",
+          removeOne<Nat>(fromArray<Nat>([3,10]), eq(0)),
+          Matchers.equals(T.optional<Nat>(T.natTestable, null))),
+        Suite.test("remove/empty",
+          toArray_(remove<Nat>(empty<Nat>(), eq(10))),
+          Matchers.equals(T.array<Nat>(T.natTestable, []))),
+        Suite.test("remove/one",
+          toArray_(remove<Nat>(make<Nat>(10), eq(10))),
+          Matchers.equals(T.array<Nat>(T.natTestable, []))),
+        Suite.test("remove/one_1",
+          toArray_(remove<Nat>(make<Nat>(0), eq(10))),
+          Matchers.equals(T.array<Nat>(T.natTestable, [0]))),
+        Suite.test("remove/two",
+          toArray_(remove<Nat>(fromArray<Nat>([3,10]), eq(3))),
+          Matchers.equals(T.array<Nat>(T.natTestable, [10]))),
+        Suite.test("remove/two_1",
+          toArray_(remove<Nat>(fromArray<Nat>([3,10]), eq(10))),
+          Matchers.equals(T.array<Nat>(T.natTestable, [3]))),
+        Suite.test("remove/two_2",
+          toArray_(remove<Nat>(fromArray<Nat>([3,10]), eq(0))),
+          Matchers.equals(T.array<Nat>(T.natTestable, [3, 10]))),
+     ]);
+
+    Suite.suite("Queue", [ to_array_test, size_test, removal_test ]);
+  }
+
+}
+
diff --git a/test/Makefile b/test/Makefile
new file mode 100644
index 0000000..5e34c7f
--- /dev/null
+++ b/test/Makefile
@@ -0,0 +1,20 @@
+TESTS=Queue
+TARGETS=$(TESTS:%=run/%)
+OBJS=$(TESTS:%=dist/%.wasm)
+
+all: $(TARGETS)
+
+run/%: dist/%.wasm
+	wasmtime $<
+
+dist:
+	@mkdir -p $@
+
+dist/%.wasm: %.mo ../src/%.mo | dist
+	moc $$(vessel sources) -wasi-system-api -o $@ $<
+
+clean:
+	rm -rf dist
+
+.PHONY: all clean
+.PRECIOUS: ${OBJS}
diff --git a/test/Queue.mo b/test/Queue.mo
new file mode 100644
index 0000000..0753306
--- /dev/null
+++ b/test/Queue.mo
@@ -0,0 +1,5 @@
+import Queue "../src/Queue";
+
+import Suite "mo:matchers/Suite";
+
+Suite.run(Queue.test())
diff --git a/vessel.dhall b/vessel.dhall
new file mode 100644
index 0000000..19be4cd
--- /dev/null
+++ b/vessel.dhall
@@ -0,0 +1,4 @@
+{
+  dependencies = [ "base", "matchers" ],
+  compiler = None Text
+}