Add a new Transducer module built on the one for graphs

Mainate.cabal

@@ -20,6 +20,7 @@ extra-source-files:  CHANGELOG.md
 library
   exposed-modules:   Graph
                    , Stream
+                   , Transducer
                    , Tree
   -- other-modules:
   -- other-extensions:

src/Transducer.hs

@@ -0,0 +1,23 @@
+module Transducer (
+      Transducer
+    , fromList
+    , run
+  ) where
+
+import Stream (Stream)
+import Graph (Graph, editLabel, open, rewind, singleton, weave)
+
+type Transducer input output = Graph input [output]
+
+empty :: Transducer input output
+empty = open $ singleton []
+
+add :: Ord input => Transducer input output -> ([input], output) -> Transducer input output
+add transducer (path, output) =
+  rewind $ editLabel (weave transducer path) (output:)
+
+fromList :: Ord input => [([input], output)] -> Transducer input output
+fromList = foldl add empty
+
+run :: Ord input => Transducer input output -> Stream input -> Stream output
+run = undefined