diff --git a/LICENSE b/LICENSE
index bb308cc..30a891b 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,6 +1,7 @@
 MIT License
 
 Copyright (c) 2015-2017 mechairoi
+Copyright (c) The University of Glasgow (Documentation)
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
diff --git a/bower.json b/bower.json
index 94e3c4b..d11a160 100644
--- a/bower.json
+++ b/bower.json
@@ -18,7 +18,8 @@
   ],
   "dependencies": {
     "purescript-prelude": "^6.0.0",
-    "purescript-effect": "^4.0.0"
+    "purescript-effect": "^4.0.0",
+    "purescript-refs": "^6.0.0"
   },
   "devDependencies": {
     "purescript-console": "^6.0.0",
diff --git a/purs.json b/purs.json
index 5a56abf..38bf7b9 100644
--- a/purs.json
+++ b/purs.json
@@ -16,6 +16,7 @@
   "description": "Data.Unique for PureScript",
   "dependencies": {
     "prelude": ">=6.0.0 <7.0.0",
-    "effect": ">=4.0.0 <5.0.0"
+    "effect": ">=4.0.0 <5.0.0",
+    "refs": ">=6.0.0 <7.0.0"
   }
 }
diff --git a/spago.dhall b/spago.dhall
index 5c9df4c..4dff66e 100644
--- a/spago.dhall
+++ b/spago.dhall
@@ -1,5 +1,5 @@
 { name = "unique"
-, dependencies = [ "effect", "prelude" ]
+, dependencies = [ "effect", "prelude", "refs" ]
 , packages = ./packages.dhall
 , sources = [ "src/**/*.purs" ]
 }
diff --git a/src/Data/Unique.js b/src/Data/Unique.js
index c541d5d..0f2ae6a 100644
--- a/src/Data/Unique.js
+++ b/src/Data/Unique.js
@@ -1,27 +1,29 @@
-/* global exports */
-"use strict";
+export var zero = BigInt("0");
 
-// module Data.Unique
+var one = BigInt("1");
 
-var MAX_SAFE_INTEGER = 9007199254740991;
-var uniqueSource = [];
-
-function iter(i) {
-  if (uniqueSource.length === i) {
-    for (var j = 0; j < i; ++j) uniqueSource[j] = 0;
-    uniqueSource[i] = 1;
-  } else {
-    if (uniqueSource[i] === MAX_SAFE_INTEGER) {
-      uniqueSource[i] = 0;
-      iter(i + 1);
-    } else {
-      uniqueSource[i]++;
-    }
-  }
+export function eqImpl(a) {
+  return function(b) {
+    return a === b;
+  };
 }
 
-export function newUnique() {
-  iter(0);
-  return uniqueSource.length === 1 ? uniqueSource[0] + "" : uniqueSource.join(",");
-};
+export function ordImpl(lt) {
+  return function (eq) {
+    return function (gt) {
+      return function (x) {
+        return function (y) {
+          return x < y ? lt : x === y ? eq : gt;
+        };
+      };
+    };
+  };
+}
 
+export function addOne(x) {
+  return x + one;
+}
+
+export function hashUnique(x) {
+  return parseInt(BigInt.asIntN(32, x));
+}
\ No newline at end of file
diff --git a/src/Data/Unique.purs b/src/Data/Unique.purs
index 21dc7d8..a84706b 100644
--- a/src/Data/Unique.purs
+++ b/src/Data/Unique.purs
@@ -1,20 +1,41 @@
-module Data.Unique
-  ( newUnique
-  , Unique
-  ) where
+module Data.Unique (Unique, hashUnique, newUnique) where
+
+import Prelude hiding (zero)
 
 import Effect (Effect)
-import Prelude (class Ord, class Eq, class Show, compare, (==))
+import Effect.Ref (Ref)
+import Effect.Ref as Ref
+import Effect.Unsafe (unsafePerformEffect)
 
-newtype Unique = Unique String
+-- | An abstract unique object.  Objects of type `Unique` may be compared for
+-- | equality and ordering and hashed into `Int`.
+foreign import data Unique :: Type
 
-foreign import newUnique :: Effect Unique
+foreign import eqImpl :: Unique -> Unique -> Boolean
 
-instance showUnique :: Show Unique where
-  show (Unique a) = a
+instance Eq Unique where
+  eq = eqImpl
 
-instance eqUnique :: Eq Unique where
-  eq (Unique a) (Unique b) = a == b
+foreign import ordImpl :: Ordering -> Ordering -> Ordering -> Unique -> Unique -> Ordering
 
-instance ordUnique :: Ord Unique where
-  compare (Unique a) (Unique b) = compare a b
+instance Ord Unique where
+  compare = ordImpl LT EQ GT
+
+foreign import addOne :: Unique -> Unique
+
+foreign import zero :: Unique
+
+-- | Hashes a `Unique` into an `Int`.  Two `Unique`s may hash to the same value,
+-- | although in practice this is unlikely.  The `Int` returned makes a good hash
+-- | key.
+foreign import hashUnique :: Unique -> Int
+
+uniqSource :: Ref Unique
+uniqSource = unsafePerformEffect (Ref.new zero)
+
+-- | Creates a new object of type `Unique`.  The value returned will not compare
+-- | equal to any other value of type `Unique` returned by previous calls to
+-- | `newUnique`. There is no limit on the number of times `newUnique` may be
+-- | called.
+newUnique :: Effect Unique
+newUnique = Ref.modify addOne uniqSource
\ No newline at end of file
diff --git a/test/Main.purs b/test/Main.purs
index 9d28159..cdc62ec 100644
--- a/test/Main.purs
+++ b/test/Main.purs
@@ -1,7 +1,7 @@
 module Test.Main where
 
-import Prelude ((==), ($), (/=), discard, bind, Unit)
-import Data.Unique (newUnique)
+import Prelude
+import Data.Unique (hashUnique, newUnique)
 import Test.Assert (assert)
 import Effect (Effect)
 import Effect.Console (log)
@@ -11,5 +11,7 @@ main = do
   log "Test Data.Unique"
   a <- newUnique
   b <- newUnique
-  assert $ a /= b
   assert $ a == a
+  assert $ a < b
+  assert $ hashUnique a == hashUnique a
+  assert $ hashUnique a /= hashUnique b
\ No newline at end of file