diff --git a/Data/Thrist.hs b/Data/Thrist.hs
--- a/Data/Thrist.hs
+++ b/Data/Thrist.hs
@@ -1,16 +1,23 @@
 module Data.Thrist ( Thrist (..)
                    , foldThrist
-                   , appendThrist ) where
+                   , appendThrist
+                   , mapThrist ) where
 
 import Prelude
 import Data.Monoid
+import Control.Category
 -- import Data.Char
+import Control.Arrow
 
 data Thrist :: (* -> * -> *) -> * -> * -> * where
-  Nil :: Thrist p a a
-  Cons :: p a b -> Thrist p b c -> Thrist p a c
+  Nil :: Thrist (~>) a a
+  Cons :: (a ~> b) -> Thrist (~>) b c -> Thrist (~>) a c
 
-foldThrist :: (forall i j k . p i j -> p j k -> p i k) -> p c c -> Thrist p a c -> p a c
+
+foldThrist :: (forall i j k . (i ~> j) -> (j ~> k) -> (i ~> k))
+              -> c ~> c
+              -> Thrist (~>) a c
+              -> a ~> c
 foldThrist _ v Nil = v
 foldThrist f v (Cons h t) = h `f` (foldThrist f v t)
 
@@ -22,16 +29,40 @@
 t2 = foldThrist (flip (.)) id t1
 -}
 
-appendThrist :: forall (p :: * -> * -> *) a b c .
-                Thrist p a b ->
-                Thrist p b c ->
-                Thrist p a c
+appendThrist :: forall ((~>) :: * -> * -> *) a b c .
+                Thrist (~>) a b ->
+                Thrist (~>) b c ->
+                Thrist (~>) a c
 
 appendThrist Nil a = a
 appendThrist (Cons b r) a = Cons b (appendThrist r a)
 
+mapThrist :: (forall i j . i +> j -> i ~> j) -> Thrist (+>) a b -> Thrist (~>) a b
+mapThrist _ Nil = Nil
+mapThrist f (Cons a r) = Cons (f a) (mapThrist f r)
 
-instance Monoid (Thrist p a a) where
+
+instance Monoid (Thrist (~>) a a) where
   mempty = Nil
   mappend = appendThrist
 
+instance Arrow (Thrist (->)) where
+  arr f = Cons f Nil
+  first Nil = Nil
+  first (Cons f _) = Cons (f *** Control.Category.id) undefined
+
+{-
+class Category cat where
+  id :: cat a a
+  (.) :: cat b c -> cat a b -> cat a c
+  (<<<) :: Category cat => cat b c -> cat a b -> cat a c
+  (>>>) :: Category cat => cat a b -> cat b c -> cat a c
+-}
+
+instance Category (Thrist (~>)) where
+  id = Nil
+  b . a = appendThrist a b
+  --  below methods are defaulted:
+  --
+  ---  b <<< a = appendThrist a b
+  ---  a >>> b = appendThrist a b
diff --git a/LICENSE b/LICENSE
--- a/LICENSE
+++ b/LICENSE
@@ -1,4 +1,4 @@
-Copyright (c) 2008 Gabor Greif
+Copyright (c) 2008-2009 Gabor Greif
 
 All rights reserved.
 
diff --git a/thrist.cabal b/thrist.cabal
--- a/thrist.cabal
+++ b/thrist.cabal
@@ -1,5 +1,5 @@
 Name:                thrist
-Version:             0.1
+Version:             0.1.1
 Synopsis:            Type-threaded list
 
 Description:
@@ -22,18 +22,18 @@
 Category:            Data Structures
 License:             BSD3
 License-File:        LICENSE
-Copyright:           (c) 2008 Gabor Greif
+Copyright:           (c) 2008-2009 Gabor Greif
 
 Author:              Gabor Greif
 Maintainer:          ggreif@gmail.com
 Homepage:            http://heisenbug.blogspot.com/search/label/thrist
 
 Stability:           experimental
-Build-Depends:       base
-Extensions:          GADTs, RankNTypes, KindSignatures, FlexibleInstances
+Build-Depends:       base >= 4 && < 5
+Extensions:          GADTs, RankNTypes, KindSignatures, FlexibleInstances, TypeOperators, FlexibleContexts
 
 Exposed-Modules:     Data.Thrist
 Ghc-Options:         -Wall
+Cabal-Version:       >= 1.2.3
 
 Build-Type:          Simple
-