diff --git a/examples/NanoFeldspar/Core.hs b/examples/NanoFeldspar/Core.hs
--- a/examples/NanoFeldspar/Core.hs
+++ b/examples/NanoFeldspar/Core.hs
@@ -135,15 +135,16 @@
 newtype Data a = Data { unData :: ASTF FeldDomainAll a }
 
 -- | Declaring 'Data' as syntactic sugar
-instance Type a => Syntactic (Data a) FeldDomainAll
+instance Type a => Syntactic (Data a)
   where
+    type Domain (Data a)   = FeldDomainAll
     type Internal (Data a) = a
     desugar = unData
     sugar   = Data
 
 -- | Specialization of the 'Syntactic' class for the Feldspar domain
-class    (Syntactic a FeldDomainAll, Type (Internal a)) => Syntax a
-instance (Syntactic a FeldDomainAll, Type (Internal a)) => Syntax a
+class    (Syntactic a, Domain a ~ FeldDomainAll, Type (Internal a)) => Syntax a
+instance (Syntactic a, Domain a ~ FeldDomainAll, Type (Internal a)) => Syntax a
 
 -- | A predicate deciding which constructs can be shared. Variables, lambdas and literals are not
 -- shared.
@@ -163,23 +164,23 @@
 --------------------------------------------------------------------------------
 
 -- | Show the expression
-showExpr :: Syntactic a FeldDomainAll => a -> String
+showExpr :: (Syntactic a, Domain a ~ FeldDomainAll) => a -> String
 showExpr = render . reifySmart canShareDict
 
 -- | Print the expression
-printExpr :: Syntactic a FeldDomainAll => a -> IO ()
+printExpr :: (Syntactic a, Domain a ~ FeldDomainAll) => a -> IO ()
 printExpr = Syntactic.printExpr . reifySmart canShareDict
 
 -- | Draw the syntax tree using ASCII
-showAST :: Syntactic a FeldDomainAll => a -> String
+showAST :: (Syntactic a, Domain a ~ FeldDomainAll) => a -> String
 showAST = Syntactic.showAST . reifySmart canShareDict
 
 -- | Draw the syntax tree on the terminal using ASCII
-drawAST :: Syntactic a FeldDomainAll => a -> IO ()
+drawAST :: (Syntactic a, Domain a ~ FeldDomainAll) => a -> IO ()
 drawAST = Syntactic.drawAST . reifySmart canShareDict
 
 -- | Evaluation
-eval :: Syntactic a FeldDomainAll => a -> Internal a
+eval :: (Syntactic a, Domain a ~ FeldDomainAll) => a -> Internal a
 eval = evalBind . reifySmart canShareDict
 
 
diff --git a/examples/NanoFeldspar/Extra.hs b/examples/NanoFeldspar/Extra.hs
--- a/examples/NanoFeldspar/Extra.hs
+++ b/examples/NanoFeldspar/Extra.hs
@@ -36,7 +36,7 @@
 canShare2 _  = True
 
 -- | Draw the syntax graph after common sub-expression elimination
-drawCSE :: Syntactic a FeldDomainAll => a -> IO ()
+drawCSE :: (Syntactic a, Domain a ~ FeldDomainAll) => a -> IO ()
 drawCSE a = do
     (g,_) <- reifyGraph canShare2 a
     drawASG
@@ -46,7 +46,7 @@
       $ g
 
 -- | Draw the syntax graph after observing sharing
-drawObs :: Syntactic a FeldDomainAll => a -> IO ()
+drawObs :: (Syntactic a, Domain a ~ FeldDomainAll) => a -> IO ()
 drawObs a = do
     (g,_) <- reifyGraph canShare2 a
     drawASG
@@ -77,6 +77,6 @@
       _ -> expr
     ) expr
 
-drawPart :: Syntactic a FeldDomainAll => a -> IO ()
+drawPart :: (Syntactic a, Domain a ~ FeldDomainAll) => a -> IO ()
 drawPart = Syntactic.drawAST . optimize constFold . reify
 
diff --git a/examples/NanoFeldspar/Vector.hs b/examples/NanoFeldspar/Vector.hs
--- a/examples/NanoFeldspar/Vector.hs
+++ b/examples/NanoFeldspar/Vector.hs
@@ -31,8 +31,9 @@
   where
     Indexed :: Data Length -> (Data Index -> a) -> Vector a
 
-instance Syntax a => Syntactic (Vector a) FeldDomainAll
+instance Syntax a => Syntactic (Vector a)
   where
+    type Domain (Vector a)   = FeldDomainAll
     type Internal (Vector a) = [Internal a]
     desugar = desugar . freezeVector . map resugar
     sugar   = map resugar . unfreezeVector . sugar
diff --git a/src/Language/Syntactic/Constructs/Binding/HigherOrder.hs b/src/Language/Syntactic/Constructs/Binding/HigherOrder.hs
--- a/src/Language/Syntactic/Constructs/Binding/HigherOrder.hs
+++ b/src/Language/Syntactic/Constructs/Binding/HigherOrder.hs
@@ -55,14 +55,15 @@
 lambda = injC . HOLambda
 
 instance
-    ( Syntactic a (HODomain dom p pVar)
-    , Syntactic b (HODomain dom p pVar)
+    ( Syntactic a, Domain a ~ HODomain dom p pVar
+    , Syntactic b, Domain b ~ HODomain dom p pVar
     , p (Internal a -> Internal b)
     , p (Internal a)
     , pVar (Internal a)
     ) =>
-      Syntactic (a -> b) (HODomain dom p pVar)
+      Syntactic (a -> b)
   where
+    type Domain (a -> b)   = Domain a
     type Internal (a -> b) = Internal a -> Internal b
     desugar f = lambda (desugar . f . sugar)
     sugar     = error "sugar not implemented for (a -> b)"
@@ -91,6 +92,7 @@
   -- variables) in the argument. This is guaranteed by the exported interface.
 
 -- | Reify an n-ary syntactic function
-reify :: Syntactic a (HODomain dom p pVar) => a -> ASTF (FODomain dom p pVar) (Internal a)
+reify :: (Syntactic a, Domain a ~ HODomain dom p pVar) =>
+    a -> ASTF (FODomain dom p pVar) (Internal a)
 reify = reifyTop . desugar
 
diff --git a/src/Language/Syntactic/Frontend/Monad.hs b/src/Language/Syntactic/Frontend/Monad.hs
--- a/src/Language/Syntactic/Frontend/Monad.hs
+++ b/src/Language/Syntactic/Frontend/Monad.hs
@@ -65,15 +65,17 @@
     -> Mon dom pVar m (ASTF (HODomain dom Typeable pVar) a)
 sugarMonad ma = Mon $ cont $ sugarSymC Bind ma
 
-instance ( Syntactic a (HODomain dom Typeable pVar)
+instance ( Syntactic a
+         , Domain a ~ HODomain dom Typeable pVar
          , InjectC (MONAD m) dom (m (Internal a))
          , Monad m
          , Typeable1 m
          , Typeable (Internal a)
          , pVar (Internal a)
          ) =>
-           Syntactic (Mon dom pVar m a) (HODomain dom Typeable pVar)
+           Syntactic (Mon dom pVar m a)
   where
+    type Domain (Mon dom pVar m a)   = Domain a
     type Internal (Mon dom pVar m a) = m (Internal a)
     desugar = desugarMonad . fmap desugar
     sugar   = fmap sugar   . sugarMonad
diff --git a/src/Language/Syntactic/Frontend/Tuple.hs b/src/Language/Syntactic/Frontend/Tuple.hs
--- a/src/Language/Syntactic/Frontend/Tuple.hs
+++ b/src/Language/Syntactic/Frontend/Tuple.hs
@@ -13,8 +13,8 @@
 
 
 instance
-    ( Syntactic a dom
-    , Syntactic b dom
+    ( Syntactic a, Domain a ~ dom
+    , Syntactic b, Domain b ~ dom
     , InjectC Tuple dom
         ( Internal a
         , Internal b
@@ -22,8 +22,9 @@
     , InjectC Select dom (Internal a)
     , InjectC Select dom (Internal b)
     ) =>
-      Syntactic (a,b) dom
+      Syntactic (a,b)
   where
+    type Domain (a,b) = Domain a
     type Internal (a,b) =
         ( Internal a
         , Internal b
@@ -36,9 +37,9 @@
         )
 
 instance
-    ( Syntactic a dom
-    , Syntactic b dom
-    , Syntactic c dom
+    ( Syntactic a, Domain a ~ dom
+    , Syntactic b, Domain b ~ dom
+    , Syntactic c, Domain c ~ dom
     , InjectC Tuple dom
         ( Internal a
         , Internal b
@@ -48,8 +49,9 @@
     , InjectC Select dom (Internal b)
     , InjectC Select dom (Internal c)
     ) =>
-      Syntactic (a,b,c) dom
+      Syntactic (a,b,c)
   where
+    type Domain (a,b,c) = Domain a
     type Internal (a,b,c) =
         ( Internal a
         , Internal b
@@ -64,10 +66,10 @@
         )
 
 instance
-    ( Syntactic a dom
-    , Syntactic b dom
-    , Syntactic c dom
-    , Syntactic d dom
+    ( Syntactic a, Domain a ~ dom
+    , Syntactic b, Domain b ~ dom
+    , Syntactic c, Domain c ~ dom
+    , Syntactic d, Domain d ~ dom
     , InjectC Tuple dom
         ( Internal a
         , Internal b
@@ -79,8 +81,9 @@
     , InjectC Select dom (Internal c)
     , InjectC Select dom (Internal d)
     ) =>
-      Syntactic (a,b,c,d) dom
+      Syntactic (a,b,c,d)
   where
+    type Domain (a,b,c,d) = Domain a
     type Internal (a,b,c,d) =
         ( Internal a
         , Internal b
@@ -97,11 +100,11 @@
         )
 
 instance
-    ( Syntactic a dom
-    , Syntactic b dom
-    , Syntactic c dom
-    , Syntactic d dom
-    , Syntactic e dom
+    ( Syntactic a, Domain a ~ dom
+    , Syntactic b, Domain b ~ dom
+    , Syntactic c, Domain c ~ dom
+    , Syntactic d, Domain d ~ dom
+    , Syntactic e, Domain e ~ dom
     , InjectC Tuple dom
         ( Internal a
         , Internal b
@@ -115,8 +118,9 @@
     , InjectC Select dom (Internal d)
     , InjectC Select dom (Internal e)
     ) =>
-      Syntactic (a,b,c,d,e) dom
+      Syntactic (a,b,c,d,e)
   where
+    type Domain (a,b,c,d,e) = Domain a
     type Internal (a,b,c,d,e) =
         ( Internal a
         , Internal b
@@ -135,12 +139,12 @@
         )
 
 instance
-    ( Syntactic a dom
-    , Syntactic b dom
-    , Syntactic c dom
-    , Syntactic d dom
-    , Syntactic e dom
-    , Syntactic f dom
+    ( Syntactic a, Domain a ~ dom
+    , Syntactic b, Domain b ~ dom
+    , Syntactic c, Domain c ~ dom
+    , Syntactic d, Domain d ~ dom
+    , Syntactic e, Domain e ~ dom
+    , Syntactic f, Domain f ~ dom
     , InjectC Tuple dom
         ( Internal a
         , Internal b
@@ -156,8 +160,9 @@
     , InjectC Select dom (Internal e)
     , InjectC Select dom (Internal f)
     ) =>
-      Syntactic (a,b,c,d,e,f) dom
+      Syntactic (a,b,c,d,e,f)
   where
+    type Domain (a,b,c,d,e,f) = Domain a
     type Internal (a,b,c,d,e,f) =
         ( Internal a
         , Internal b
@@ -178,13 +183,13 @@
         )
 
 instance
-    ( Syntactic a dom
-    , Syntactic b dom
-    , Syntactic c dom
-    , Syntactic d dom
-    , Syntactic e dom
-    , Syntactic f dom
-    , Syntactic g dom
+    ( Syntactic a, Domain a ~ dom
+    , Syntactic b, Domain b ~ dom
+    , Syntactic c, Domain c ~ dom
+    , Syntactic d, Domain d ~ dom
+    , Syntactic e, Domain e ~ dom
+    , Syntactic f, Domain f ~ dom
+    , Syntactic g, Domain g ~ dom
     , InjectC Tuple dom
         ( Internal a
         , Internal b
@@ -202,8 +207,9 @@
     , InjectC Select dom (Internal f)
     , InjectC Select dom (Internal g)
     ) =>
-      Syntactic (a,b,c,d,e,f,g) dom
+      Syntactic (a,b,c,d,e,f,g)
   where
+    type Domain (a,b,c,d,e,f,g) = Domain a
     type Internal (a,b,c,d,e,f,g) =
         ( Internal a
         , Internal b
diff --git a/src/Language/Syntactic/Frontend/TupleConstrained.hs b/src/Language/Syntactic/Frontend/TupleConstrained.hs
--- a/src/Language/Syntactic/Frontend/TupleConstrained.hs
+++ b/src/Language/Syntactic/Frontend/TupleConstrained.hs
@@ -46,8 +46,8 @@
 
 
 instance
-    ( Syntactic a dom
-    , Syntactic b dom
+    ( Syntactic a, Domain a ~ dom
+    , Syntactic b, Domain b ~ dom
     , TupleSat dom p
     , p (Internal a, Internal b)
     , p (Internal a)
@@ -59,8 +59,9 @@
     , InjectC (Select :|| p) dom (Internal a)
     , InjectC (Select :|| p) dom (Internal b)
     ) =>
-      Syntactic (a,b) dom
+      Syntactic (a,b)
   where
+    type Domain (a,b) = Domain a
     type Internal (a,b) =
         ( Internal a
         , Internal b
@@ -73,9 +74,9 @@
         )
 
 instance
-    ( Syntactic a dom
-    , Syntactic b dom
-    , Syntactic c dom
+    ( Syntactic a, Domain a ~ dom
+    , Syntactic b, Domain b ~ dom
+    , Syntactic c, Domain c ~ dom
     , TupleSat dom p
     , p ( Internal a
         , Internal b
@@ -93,8 +94,9 @@
     , InjectC (Select :|| p) dom (Internal b)
     , InjectC (Select :|| p) dom (Internal c)
     ) =>
-      Syntactic (a,b,c) dom
+      Syntactic (a,b,c)
   where
+    type Domain (a,b,c) = Domain a
     type Internal (a,b,c) =
         ( Internal a
         , Internal b
@@ -109,10 +111,10 @@
         )
 
 instance
-    ( Syntactic a dom
-    , Syntactic b dom
-    , Syntactic c dom
-    , Syntactic d dom
+    ( Syntactic a, Domain a ~ dom
+    , Syntactic b, Domain b ~ dom
+    , Syntactic c, Domain c ~ dom
+    , Syntactic d, Domain d ~ dom
     , TupleSat dom p
     , p ( Internal a
         , Internal b
@@ -134,8 +136,9 @@
     , InjectC (Select :|| p) dom (Internal c)
     , InjectC (Select :|| p) dom (Internal d)
     ) =>
-      Syntactic (a,b,c,d) dom
+      Syntactic (a,b,c,d)
   where
+    type Domain (a,b,c,d) = Domain a
     type Internal (a,b,c,d) =
         ( Internal a
         , Internal b
@@ -152,11 +155,11 @@
         )
 
 instance
-    ( Syntactic a dom
-    , Syntactic b dom
-    , Syntactic c dom
-    , Syntactic d dom
-    , Syntactic e dom
+    ( Syntactic a, Domain a ~ dom
+    , Syntactic b, Domain b ~ dom
+    , Syntactic c, Domain c ~ dom
+    , Syntactic d, Domain d ~ dom
+    , Syntactic e, Domain e ~ dom
     , TupleSat dom p
     , p ( Internal a
         , Internal b
@@ -182,8 +185,9 @@
     , InjectC (Select :|| p) dom (Internal d)
     , InjectC (Select :|| p) dom (Internal e)
     ) =>
-      Syntactic (a,b,c,d,e) dom
+      Syntactic (a,b,c,d,e)
   where
+    type Domain (a,b,c,d,e) = Domain a
     type Internal (a,b,c,d,e) =
         ( Internal a
         , Internal b
@@ -202,12 +206,12 @@
         )
 
 instance
-    ( Syntactic a dom
-    , Syntactic b dom
-    , Syntactic c dom
-    , Syntactic d dom
-    , Syntactic e dom
-    , Syntactic f dom
+    ( Syntactic a, Domain a ~ dom
+    , Syntactic b, Domain b ~ dom
+    , Syntactic c, Domain c ~ dom
+    , Syntactic d, Domain d ~ dom
+    , Syntactic e, Domain e ~ dom
+    , Syntactic f, Domain f ~ dom
     , TupleSat dom p
     , p ( Internal a
         , Internal b
@@ -237,8 +241,9 @@
     , InjectC (Select :|| p) dom (Internal e)
     , InjectC (Select :|| p) dom (Internal f)
     ) =>
-      Syntactic (a,b,c,d,e,f) dom
+      Syntactic (a,b,c,d,e,f)
   where
+    type Domain (a,b,c,d,e,f) = Domain a
     type Internal (a,b,c,d,e,f) =
         ( Internal a
         , Internal b
@@ -259,13 +264,13 @@
         )
 
 instance
-    ( Syntactic a dom
-    , Syntactic b dom
-    , Syntactic c dom
-    , Syntactic d dom
-    , Syntactic e dom
-    , Syntactic f dom
-    , Syntactic g dom
+    ( Syntactic a, Domain a ~ dom
+    , Syntactic b, Domain b ~ dom
+    , Syntactic c, Domain c ~ dom
+    , Syntactic d, Domain d ~ dom
+    , Syntactic e, Domain e ~ dom
+    , Syntactic f, Domain f ~ dom
+    , Syntactic g, Domain g ~ dom
     , TupleSat dom p
     , p ( Internal a
         , Internal b
@@ -299,8 +304,9 @@
     , InjectC (Select :|| p) dom (Internal f)
     , InjectC (Select :|| p) dom (Internal g)
     ) =>
-      Syntactic (a,b,c,d,e,f,g) dom
+      Syntactic (a,b,c,d,e,f,g)
   where
+    type Domain (a,b,c,d,e,f,g) = Domain a
     type Internal (a,b,c,d,e,f,g) =
         ( Internal a
         , Internal b
diff --git a/src/Language/Syntactic/Sharing/ReifyHO.hs b/src/Language/Syntactic/Sharing/ReifyHO.hs
--- a/src/Language/Syntactic/Sharing/ReifyHO.hs
+++ b/src/Language/Syntactic/Sharing/ReifyHO.hs
@@ -100,7 +100,7 @@
 -- This function is not referentially transparent (hence the 'IO'). However, it
 -- is well-behaved in the sense that the worst thing that could happen is that
 -- sharing is lost. It is not possible to get false sharing.
-reifyGraph :: Syntactic a (HODomain dom p pVar)
+reifyGraph :: (Syntactic a, Domain a ~ HODomain dom p pVar)
     => (forall a . ASTF (HODomain dom p pVar) a -> Bool)
          -- ^ A function that decides whether a given node can be shared
     -> a
diff --git a/src/Language/Syntactic/Sharing/SimpleCodeMotion.hs b/src/Language/Syntactic/Sharing/SimpleCodeMotion.hs
--- a/src/Language/Syntactic/Sharing/SimpleCodeMotion.hs
+++ b/src/Language/Syntactic/Sharing/SimpleCodeMotion.hs
@@ -191,7 +191,8 @@
 -- | Like 'reify' but with common sub-expression elimination and variable hoisting
 reifySmart :: forall dom p pVar a
     .  ( AlphaEq dom dom (FODomain dom p pVar) [(VarId,VarId)]
-       , Syntactic a (HODomain dom p pVar)
+       , Syntactic a
+       , Domain a ~ HODomain dom p pVar
        , p :< Typeable
        )
     => MkInjDict (FODomain dom p pVar)
diff --git a/src/Language/Syntactic/Sugar.hs b/src/Language/Syntactic/Sugar.hs
--- a/src/Language/Syntactic/Sugar.hs
+++ b/src/Language/Syntactic/Sugar.hs
@@ -14,24 +14,22 @@
 
 -- | It is usually assumed that @(`desugar` (`sugar` a))@ has the same meaning
 -- as @a@.
-class Syntactic a dom | a -> dom
-    -- Note: using a functional dependency rather than an associated type,
-    -- because this makes it possible to make a class alias constraining dom.
-    -- TODO Now that GHC allows equality super class constraints, this should be
-    --      changed to an associated type.
+class Syntactic a
   where
+    type Domain a :: * -> *
     type Internal a
-    desugar :: a -> ASTF dom (Internal a)
-    sugar   :: ASTF dom (Internal a) -> a
+    desugar :: a -> ASTF (Domain a) (Internal a)
+    sugar   :: ASTF (Domain a) (Internal a) -> a
 
-instance Syntactic (ASTF dom a) dom
+instance Syntactic (ASTF dom a)
   where
+    type Domain (ASTF dom a)   = dom
     type Internal (ASTF dom a) = a
     desugar = id
     sugar   = id
 
 -- | Syntactic type casting
-resugar :: (Syntactic a dom, Syntactic b dom, Internal a ~ Internal b) => a -> b
+resugar :: (Syntactic a, Syntactic b, Domain a ~ Domain b, Internal a ~ Internal b) => a -> b
 resugar = sugar . desugar
 
 -- | N-ary syntactic functions
@@ -39,10 +37,14 @@
 -- 'desugarN' has any type of the form:
 --
 -- > desugarN ::
--- >     ( Syntactic a dom
--- >     , Syntactic b dom
+-- >     ( Syntactic a
+-- >     , Syntactic b
 -- >     , ...
--- >     , Syntactic x dom
+-- >     , Syntactic x
+-- >     , Domain a ~ dom
+-- >     , Domain b ~ dom
+-- >     , ...
+-- >     , Domain x ~ dom
 -- >     ) => (a -> b -> ... -> x)
 -- >       -> (  ASTF dom (Internal a)
 -- >          -> ASTF dom (Internal b)
@@ -56,13 +58,14 @@
     desugarN :: a -> internal
     sugarN   :: internal -> a
 
-instance (Syntactic a dom, ia ~ AST dom (Full (Internal a))) => SyntacticN a ia
+instance (Syntactic a, Domain a ~ dom, ia ~ AST dom (Full (Internal a))) => SyntacticN a ia
   where
     desugarN = desugar
     sugarN   = sugar
 
 instance
-    ( Syntactic a dom
+    ( Syntactic a
+    , Domain a ~ dom
     , ia ~ Internal a
     , SyntacticN b ib
     ) =>
diff --git a/src/Language/Syntactic/Syntax.hs b/src/Language/Syntactic/Syntax.hs
--- a/src/Language/Syntactic/Syntax.hs
+++ b/src/Language/Syntactic/Syntax.hs
@@ -1,6 +1,8 @@
 {-# LANGUAGE OverlappingInstances #-}
 {-# LANGUAGE UndecidableInstances #-}
 
+{-# OPTIONS_GHC -cpp #-}
+
 -- | Generic representation of typed syntax trees
 --
 -- For details, see: A Generic Abstract Syntax Model for Embedded Languages
@@ -27,6 +29,7 @@
 
 
 
+import Control.Monad.Instances  -- Not needed in GHC 7.6
 import Data.Typeable
 
 import Data.PolyProxy
@@ -52,13 +55,18 @@
 -- | Fully applied abstract syntax tree
 type ASTF dom a = AST dom (Full a)
 
+instance Functor dom => Functor (AST dom)
+  where
+    fmap f (Sym s)  = Sym (fmap f s)
+    fmap f (s :$ a) = fmap (fmap f) s :$ a
+
 -- | Signature of a fully applied symbol
 newtype Full a = Full { result :: a }
-  deriving (Eq, Show, Typeable)
+  deriving (Eq, Show, Typeable, Functor)
 
 -- | Signature of a partially applied (or unapplied) symbol
 newtype a :-> sig = Partial (a -> sig)
-  deriving (Typeable)
+  deriving (Typeable, Functor)
 
 infixr :->
 
@@ -96,6 +104,7 @@
   where
     InjL :: dom1 a -> (dom1 :+: dom2) a
     InjR :: dom2 a -> (dom1 :+: dom2) a
+  deriving (Functor)
 
 infixr :+:
 
diff --git a/syntactic.cabal b/syntactic.cabal
--- a/syntactic.cabal
+++ b/syntactic.cabal
@@ -1,5 +1,5 @@
 Name:           syntactic
-Version:        1.2.1
+Version:        1.3
 Synopsis:       Generic abstract syntax, and utilities for embedded languages
 Description:    This library provides:
                 .