diff --git a/Data/Thrist.hs b/Data/Thrist.hs
--- a/Data/Thrist.hs
+++ b/Data/Thrist.hs
@@ -1,7 +1,9 @@
-module Data.Thrist( Thrist(..)
-                  , foldThrist ) where
+module Data.Thrist ( Thrist (..)
+                   , foldThrist
+                   , appendThrist ) where
 
 import Prelude
+import Data.Monoid
 -- import Data.Char
 
 data Thrist :: (* -> * -> *) -> * -> * -> * where
@@ -19,4 +21,17 @@
 t2 :: Char -> Char
 t2 = foldThrist (flip (.)) id t1
 -}
+
+appendThrist :: forall (p :: * -> * -> *) a b c .
+                Thrist p a b ->
+                Thrist p b c ->
+                Thrist p a c
+
+appendThrist Nil a = a
+appendThrist (Cons b r) a = Cons b (appendThrist r a)
+
+
+instance Monoid (Thrist p a a) where
+  mempty = Nil
+  mappend = appendThrist
 
diff --git a/thrist.cabal b/thrist.cabal
--- a/thrist.cabal
+++ b/thrist.cabal
@@ -1,5 +1,5 @@
 Name:                thrist
-Version:             0.0
+Version:             0.1
 Synopsis:            Type-threaded list
 
 Description:
@@ -30,7 +30,7 @@
 
 Stability:           experimental
 Build-Depends:       base
-Extensions:          GADTs
+Extensions:          GADTs, RankNTypes, KindSignatures, FlexibleInstances
 
 Exposed-Modules:     Data.Thrist
 Ghc-Options:         -Wall