Initial commit.

src/Control/Enumerator/Base.hs

@@ -0,0 +1,84 @@
+{-# LANGUAGE Rank2Types #-}
+--import Control.Enumerator.Base where
+
+type IterateeM acc a m = acc -> a -> m (IterResult acc)
+newtype EnumeratorM m a =
+    Enum { enum :: forall acc. IterateeM acc a m -> acc -> m acc }
+
+mkEnum = Enum
+
+data IterResult a 
+    = IOk a
+    | IStop a
+
+instance Functor (EnumeratorM m) where
+    -- fmap :: (a -> b) -> EnumeratorM m a -> EnumeratorM m b
+    --       = forall r. IterateeM r a m -> r -> m r
+    --         -> forall r. IterateeM r b m -> r -> m r
+    fmap f (Enum enuma) = mkEnum $ \iter r ->
+                            let iter' r' a = iter r' (f a) in
+                            enuma iter' r
+
+-- | Concatenate two enumerators yields a new enumerator that generates the
+--  output from the first enumerator, then the output from the second
+--  enumerator.
+concatE :: Monad m => EnumeratorM m b -> EnumeratorM m b -> EnumeratorM m b
+concatE enum1 enum2 = mkEnum $ e
+  where
+    e iter initSeed = enum enum1 iter' (True, initSeed) >>= k
+      where
+        iter' (True, seed) dat = do
+          r <- iter seed dat
+          case r of
+            IOk y        -> return $ IOk (True, y)
+            IStop y      -> return $ IStop (False, y)
+        iter' (False, _) _ = error "impossible"
+        k (False, seed) = return seed
+        k (True, seed) = enum enum2 iter seed
+
+stringEnum :: Monad m => String -> Int -> EnumeratorM m String
+stringEnum str chunksize = mkEnum e 
+  where
+    e iter a = go a str
+      where
+        go a [] = return a
+        go a s = do
+          let (d,s') = splitAt chunksize s
+          r <- iter a d
+          case r of
+            IOk a'   -> go a' s'
+            IStop a' -> return a'
+
+printIter :: Show a => IterateeM () a IO
+printIter _ a = print a >> return (IOk ())
+
+countIter :: Monad m => IterateeM Int a m
+countIter n _ = return (IOk $! n + 1)
+
+--lEnum :: Monad m => EnumeratorM m String -> EnumeratorM m Int
+lEnum enumstr = mkEnum e
+  where
+    e iter a = enum enumstr iter' a
+      where
+        iter' a str = iter a (length str)
+
+
+forE :: EnumeratorM m dat -> a -> IterateeM a dat m -> m a
+forE e a i = enum e i a
+
+t001 = forE (concatE (stringEnum "foobarbaz" 5)
+                     (stringEnum "axonos" 2)) () $
+            printIter
+t002 = (forE (concatE (stringEnum "foobarbaz" 1)
+                      (stringEnum "axonos" 2)) 0 $
+            countIter)
+       >>= print
+
+t003 = forE ((\x -> (x,x)) `fmap` 
+                   concatE (stringEnum "foobarbaz" 5)
+                           (stringEnum "axonos" 2)) () $
+            printIter
+
+thenI :: IterateeM acc1 a m -> (acc1 -> a -> IterateeM acc2 a m) 
+      -> IterateeM acc2 a m
+thenI _ _ = undefined