[project @ 2005-10-05 08:43:26 by ross]

add Monad and MonadPlus instances

diff --git a/Data/Sequence.hs b/Data/Sequence.hs
index bc3a743..6f01e0d 100644 (file)
--- a/Data/Sequence.hs
+++ b/Data/Sequence.hs
@@ -81,10 +81,14 @@ import Prelude hiding (
        reverse)
 import qualified Prelude (foldr)
 import qualified Data.List (foldl', intersperse)
+import Control.Monad (MonadPlus(..))
 import Data.FunctorM
 import Data.Typeable
+
 #ifdef __GLASGOW_HASKELL__
 import GHC.Exts (build)
+import Data.Generics.Basics (Data(..), Fixity(..),
+                       constrIndex, mkConstr, mkDataType)
 #endif
 
 #if TESTING
@@ -92,11 +96,6 @@ import Control.Monad (liftM, liftM2, liftM3, liftM4)
 import Test.QuickCheck
 #endif
 
-#if __GLASGOW_HASKELL__
-import Data.Generics.Basics (Data(..), Fixity(..),
-                       constrIndex, mkConstr, mkDataType)
-#endif
-
 infixr 5 `consTree`
 infixl 5 `snocTree`
 
@@ -107,16 +106,29 @@ infixl 5 |>, :>
 class Sized a where
        size :: a -> Int
 
-------------------------------------------------------------------------
--- Random access sequences
-------------------------------------------------------------------------
-
 -- | General-purpose finite sequences.
 newtype Seq a = Seq (FingerTree (Elem a))
 
 instance Functor Seq where
        fmap f (Seq xs) = Seq (fmap (fmap f) xs)
 
+instance Monad Seq where
+       return = singleton
+       xs >>= f = foldl' add empty xs
+         where add ys x = ys >< f x
+
+instance MonadPlus Seq where
+       mzero = empty
+       mplus = (><)
+
+instance FunctorM Seq where
+       fmapM f = foldlM f' empty
+         where f' ys x = do
+                       y <- f x
+                       return $! (ys |> y)
+       fmapM_ f = foldlM f' ()
+         where f' _ x = f x >> return ()
+
 instance Eq a => Eq (Seq a) where
        xs == ys = length xs == length ys && toList xs == toList ys
 
@@ -134,14 +146,6 @@ instance Show a => Show (Seq a) where
                showChar '>'
 #endif
 
-instance FunctorM Seq where
-       fmapM f = foldlM f' empty
-         where f' ys x = do
-                       y <- f x
-                       return $! (ys |> y)
-       fmapM_ f = foldlM f' ()
-         where f' _ x = f x >> return ()
-
 #include "Typeable.h"
 INSTANCE_TYPEABLE1(Seq,seqTc,"Seq")