simple iteratee implementation

iter.hs

@@ -0,0 +1,41 @@
+import Debug.Trace
+
+data Stream a = Chunks [a]
+              | EOF
+
+data Step a b = Yield b (Stream a)
+              | Error
+              | Continue (Iteratee a b)
+
+type Iteratee a b = Stream a -> Step a b
+type Enumerator a b = Iteratee a b -> Iteratee a b
+
+consume :: Show a => Int -> Iteratee a [a]
+consume n =
+    loop [] 0
+  where
+    loop acc len
+        | len >= n  = let (a, b) = splitAt n acc
+                      in const $ Yield a (Chunks b)
+        | otherwise = \s -> case s of
+            Chunks xs -> trace (show xs) $ Continue $ loop (acc ++ xs) (len + length xs)
+            EOF       -> Yield acc EOF
+
+enumList :: Int -> [a] -> Iteratee a b -> Iteratee a b
+enumList n xs it =
+    loop xs it
+  where
+    loop [] it = it
+    loop xs it =
+        let (a, b) = splitAt n xs 
+            it1 = it (Chunks a)
+        in  case it1 of
+                Continue it2 -> loop b it2
+                _            -> const it1
+
+run :: Iteratee a b -> b
+run it = case it EOF of
+    Yield b _ -> b
+    _         -> error "non exausted iteratee"
+
+main = print $ run $ enumList 4 [1..100] $ consume 30