Expose Vertex to access label of a node from a Transducer and implement running a Transducer on some input

src/Graph.hs

@@ -2,6 +2,7 @@
 {-# LANGUAGE DeriveFunctor #-}
 module Graph (
       Graph(..)
+    , Vertex(..)
     , editLabel
     , follow
     , open

src/Transducer.hs

@@ -1,11 +1,13 @@
+{-# LANGUAGE NamedFieldPuns #-}
 module Transducer (
       Transducer
     , fromList
     , run
   ) where
 
-import Stream (Stream)
-import Graph (Graph, editLabel, open, rewind, singleton, weave)
+import Stream (Stream(..), merge)
+import qualified Stream (empty)
+import Graph (Graph(..), Vertex(..), editLabel, follow, open, rewind, singleton, weave)
 
 type Transducer input output = Graph input [output]
 
@@ -19,5 +21,12 @@ add 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
+run :: (Ord input, Eq output) => Transducer input output -> Stream input -> Stream output
+run transducer (Stream inputs) = foldl (\(Stream outputs) (input, stream) ->
+    case follow transducer input of
+      Nothing -> Stream.empty
+      Just newState@(Graph {focus}) ->
+        Stream ((emit stream <$> label focus) ++ outputs) `merge` run newState stream
+  ) Stream.empty inputs
+  where
+    emit stream output = (output, run (rewind transducer) stream)