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diff --git a/source/lux/data/either.lux b/source/lux/data/either.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/data (list #refer (#exclude partition))))
+
+## [Types]
+## (deftype (Either l r)
+##   (| (#;Left l)
+##      (#;Right r)))
+
+## [Functions]
+(def #export (either f g e)
+  (All [a b c] (-> (-> a c) (-> b c) (Either a b) c))
+  (case e
+    (#;Left x)  (f x)
+    (#;Right x) (g x)))
+
+(do-template [<name> <side> <tag>]
+  [(def #export (<name> es)
+     (All [a b] (-> (List (Either a b)) (List <side>)))
+     (case es
+       #;Nil                    #;Nil
+       (#;Cons [(<tag> x) es']) (#;Cons [x (<name> es')])
+       (#;Cons [_ es'])         (<name> es')))]
+
+  [lefts  a #;Left]
+  [rights b #;Right]
+  )
+
+(def #export (partition es)
+  (All [a b] (-> (List (Either a b)) (, (List a) (List b))))
+  (foldL (: (All [a b]
+              (-> (, (List a) (List b)) (Either a b) (, (List a) (List b))))
+            (lambda [tails e]
+              (let [[ltail rtail] tails]
+                (case e
+                  (#;Left x)  [(#;Cons [x ltail]) rtail]
+                  (#;Right x) [ltail (#;Cons [x rtail])]))))
+         [(list) (list)]
+         (reverse es)))