monads: added set monad

1 files changed, 14 insertions, 1 deletions

diff --git a/src/clojure/contrib/monads.clj b/src/clojure/contrib/monads.clj
index 3d746acf..01ee7784 100644
--- a/src/clojure/contrib/monads.clj
+++ b/src/clojure/contrib/monads.clj
@@ -1,7 +1,7 @@
 ;; Monads in Clojure
 
 ;; by Konrad Hinsen
-;; last updated March 3, 2009
+;; last updated March 6, 2009
 
 ;; Copyright (c) Konrad Hinsen, 2009. All rights reserved.  The use
 ;; and distribution terms for this software are covered by the Eclipse
@@ -243,6 +243,19 @@
                (apply concat mvs))
     ])
 
+; Set monad
+(defmonad set-m
+   "Monad describing multi-valued computations, like sequence-m,
+    but returning sets of results instead of sequences of results."
+   [m-result (fn m-result-set [v]
+	       #{v})
+    m-bind   (fn m-bind-set [mv f]
+               (apply clojure.set/union (map f mv)))
+    m-zero   #{}
+    m-plus   (fn m-plus-set [& mvs]
+               (apply clojure.set/union mvs))
+    ])
+
 ; State monad
 (defmonad state-m
    "Monad describing stateful computations. The monadic values have the