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diff --git a/source/lux/data/writer.lux b/source/lux/data/writer.lux
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+##   Copyright (c) Eduardo Julian. All rights reserved.
+##   The use and distribution terms for this software are covered by the
+##   Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
+##   which can be found in the file epl-v10.html at the root of this distribution.
+##   By using this software in any fashion, you are agreeing to be bound by
+##   the terms of this license.
+##   You must not remove this notice, or any other, from this software.
+
+(;import lux
+         (lux/control (monoid #as m #refer #all)
+                      (functor #as F #refer #all)
+                      (monad #as M #refer #all)))
+
+## [Types]
+(deftype #export (Writer l a)
+  (, l a))
+
+## [Structures]
+(defstruct #export Writer/Functor (All [l]
+                                    (Functor (Writer l)))
+  (def (F;map f fa)
+    (let [[log datum] fa]
+      [log (f datum)])))
+
+(defstruct #export (Writer/Monad mon) (All [l]
+                                        (-> (Monoid l) (Monad (Writer l))))
+  (def M;_functor Writer/Functor)
+
+  (def (M;wrap x)
+    [(:: mon m;unit) x])
+
+  (def (M;join mma)
+    (let [[log1 [log2 a]] mma]
+      [(:: mon (m;++ log1 log2)) a])))