diff --git a/backends/BackendPasses.hs b/backends/BackendPasses.hs
index b6ed884..a2056ae 100644
--- a/backends/BackendPasses.hs
+++ b/backends/BackendPasses.hs
@@ -441,7 +441,7 @@ mobileReturn = cOnlyPass "Add MOBILE returns" [] [] recurse
                      return $ surr $ A.ProcCall m n as'
     doProcess p = descend p
 
-    chanT t = A.Chan (A.ChanAttributes False False) t
+    chanT t = A.Chan (A.ChanAttributes A.Unshared A.Unshared) t
 
     addChansAct :: Meta -> [(A.Formal, A.Actual)] -> PassM (A.Process -> A.Process, [A.Actual])
     addChansAct _ [] = return (id, [])
diff --git a/backends/GenerateCPPCSP.hs b/backends/GenerateCPPCSP.hs
index a285a0e..ccd09dc 100644
--- a/backends/GenerateCPPCSP.hs
+++ b/backends/GenerateCPPCSP.hs
@@ -655,10 +655,10 @@ cppgetCType m t am | isChan t
                           A.ChanEnd A.DirOutput _ innerT -> ("csp::Chanout", innerT)
                           A.Chan attr innerT -> (
                             case (A.caWritingShared attr,A.caReadingShared attr) of
-                              (False,False) -> "csp::One2OneChannel"
-                              (False,True)  -> "csp::One2AnyChannel"
-                              (True,False)  -> "csp::Any2OneChannel"
-                              (True,True)   -> "csp::Any2AnyChannel"
+                              (A.Unshared,A.Unshared) -> "csp::One2OneChannel"
+                              (A.Unshared,A.Shared)  -> "csp::One2AnyChannel"
+                              (A.Shared,A.Unshared)  -> "csp::Any2OneChannel"
+                              (A.Shared,A.Shared)   -> "csp::Any2AnyChannel"
                             , innerT)
          innerCT <- cppTypeInsideChannel innerT
          return $ Template chanType [innerCT]
diff --git a/common/ShowCode.hs b/common/ShowCode.hs
index 7111b97..bfd3c6d 100644
--- a/common/ShowCode.hs
+++ b/common/ShowCode.hs
@@ -254,10 +254,10 @@ instance ShowOccam A.Type where
     where
       shared
           = case (A.caWritingShared ca, A.caReadingShared ca) of
-              (False, False) -> ""
-              (True, False) -> "SHARED! "
-              (False, True) -> "SHARED? "
-              (True, True) -> "SHARED "
+              (A.Unshared, A.Unshared) -> ""
+              (A.Shared, A.Unshared) -> "SHARED! "
+              (A.Unshared, A.Shared) -> "SHARED? "
+              (A.Shared, A.Shared) -> "SHARED "
       direction
           = case dir of
               A.DirInput -> "?"
@@ -267,10 +267,10 @@ instance ShowOccam A.Type where
     where
       shared
           = case (A.caWritingShared ca, A.caReadingShared ca) of
-              (False, False) -> ""
-              (True, False) -> "SHARED! "
-              (False, True) -> "SHARED? "
-              (True, True) -> "SHARED "
+              (A.Unshared, A.Unshared) -> ""
+              (A.Shared, A.Unshared) -> "SHARED! "
+              (A.Unshared, A.Shared) -> "SHARED? "
+              (A.Shared, A.Shared) -> "SHARED "
   showOccamM (A.Counted ct et) = showOccamM ct >> tell ["::"] >> showOccamM et
   showOccamM (A.Port t) = tell ["PORT "] >> showOccamM t
   showOccamM (A.UserDataType n) = showName n >> helper "{data type}"
@@ -293,12 +293,12 @@ instance ShowRain A.Type where
     = tell ["channel ", ao (A.caWritingShared attr),
           "2", ao (A.caReadingShared attr)," "] >> showRainM t
     where
-      ao :: Bool -> String
-      ao b = if b then "any" else "one"  
+      ao :: A.ShareMode -> String
+      ao b = if b == A.Shared then "any" else "one"  
   showRainM (A.ChanEnd dir attr t) 
     = case dir of
-        A.DirInput -> tell [if A.caReadingShared attr then "shared" else "", " ?"] >> showRainM t
-        A.DirOutput -> tell [if A.caWritingShared attr then "shared" else "", " !"] >> showRainM t
+        A.DirInput -> tell [if A.caReadingShared attr == A.Shared then "shared" else "", " ?"] >> showRainM t
+        A.DirOutput -> tell [if A.caWritingShared attr == A.Shared then "shared" else "", " !"] >> showRainM t
     where
       ao :: Bool -> String
       ao b = if b then "any" else "one"  
diff --git a/common/Types.hs b/common/Types.hs
index e585646..b529c4b 100644
--- a/common/Types.hs
+++ b/common/Types.hs
@@ -235,7 +235,7 @@ typeOfVariable (A.DirectedVariable m dir v)
              if dir == dir'
                then return t
                else dieP m $ "Attempted to reverse direction of a channel-end"
-           A.Infer -> return $ A.ChanEnd dir (A.ChanAttributes False False) A.Infer
+           A.Infer -> return $ A.ChanEnd dir (A.ChanAttributes A.Unshared A.Unshared) A.Infer
            _ -> diePC m $ formatCode "Direction specified on non-channel variable of type: %" t
 
 -- | Get the abbreviation mode of a variable.
diff --git a/data/AST.hs b/data/AST.hs
index ad17d03..8c9a0d5 100644
--- a/data/AST.hs
+++ b/data/AST.hs
@@ -80,10 +80,15 @@ data Direction =
   | DirOutput      -- ^ The output end.
   deriving (Show, Eq, Typeable, Data)
 
+data ShareMode
+  = Unshared
+    | Shared
+    deriving (Show, Eq, Typeable, Data)
+
 -- | Attributes of the type of a channel.
 data ChanAttributes = ChanAttributes {
-    caWritingShared :: Bool,
-    caReadingShared :: Bool
+    caWritingShared :: ShareMode,
+    caReadingShared :: ShareMode
   }
   deriving (Show, Eq, Typeable, Data)
 
diff --git a/frontends/OccamTypes.hs b/frontends/OccamTypes.hs
index dc9831d..51a9c59 100644
--- a/frontends/OccamTypes.hs
+++ b/frontends/OccamTypes.hs
@@ -433,8 +433,8 @@ checkChannel wantDir c
                   when (wantDir /= dir) $ dieP m $ "Channel directions do not match"
                   -- Check it's not shared in the direction we're using.
                   case (ws, rs, wantDir) of
-                    (False, _, A.DirOutput) -> ok
-                    (_, False, A.DirInput) -> ok
+                    (A.Unshared, _, A.DirOutput) -> ok
+                    (_, A.Unshared, A.DirInput) -> ok
                     _ -> dieP m $ "Shared channel must be claimed before use"
 
                   return innerT
diff --git a/frontends/OccamTypesTest.hs b/frontends/OccamTypesTest.hs
index 6552a5c..0899600 100644
--- a/frontends/OccamTypesTest.hs
+++ b/frontends/OccamTypesTest.hs
@@ -74,7 +74,7 @@ startState
   where
     intsT = A.Array [A.UnknownDimension] A.Int
     arrayLit = A.ArrayListLiteral m $ A.Several m []
-    chanT t = A.Chan (A.ChanAttributes False False) t
+    chanT t = A.Chan (A.ChanAttributes A.Unshared A.Unshared) t
     chanIntT = chanT A.Int
     countedIntsT = chanT $ A.UserProtocol (simpleName "countedInts")
     iirT = chanT $ A.UserProtocol (simpleName "iir")
@@ -564,7 +564,7 @@ testOccamTypes = TestList
     coord2E = A.Literal m coord2T coord2
     coord3T = A.Record (simpleName "COORD3")
     coord3 = A.RecordLiteral m [realE, realE, realE]
-    chanT t = A.Chan (A.ChanAttributes False False) t
+    chanT t = A.Chan (A.ChanAttributes A.Unshared A.Unshared) t
     chanIntT = chanT A.Int
     chansIntT = A.Array [dimension 2] $ chanT A.Int
     uchansIntT = A.Array [A.UnknownDimension] $ chanT A.Int
diff --git a/frontends/ParseOccam.hs b/frontends/ParseOccam.hs
index 113deaa..afbb922 100644
--- a/frontends/ParseOccam.hs
+++ b/frontends/ParseOccam.hs
@@ -545,7 +545,7 @@ dataType
 
 channelType :: OccParser A.Type
 channelType
-    =   do { sCHAN; optional sOF; p <- protocol; return $ A.Chan A.ChanAttributes {A.caWritingShared = False, A.caReadingShared = False} p }
+    =   do { sCHAN; optional sOF; p <- protocol; return $ A.Chan A.ChanAttributes {A.caWritingShared = A.Unshared, A.caReadingShared = A.Unshared} p }
     <|> arrayType channelType
     <?> "channel type"
 
diff --git a/frontends/ParseRain.hs b/frontends/ParseRain.hs
index 626ca4c..f42c0c1 100644
--- a/frontends/ParseRain.hs
+++ b/frontends/ParseRain.hs
@@ -167,9 +167,9 @@ dataType
     <|> do {reserved "sint32" ; return A.Int32}
     <|> do {reserved "sint64" ; return A.Int64}    
     <|> do {reserved "time" ; return A.Time}
-    <|> do {sChannel ; inner <- dataType ; return $ A.Chan (A.ChanAttributes {A.caWritingShared = False, A.caReadingShared = False}) inner}
-    <|> do {sIn ; inner <- dataType ; return $ A.ChanEnd A.DirInput (A.ChanAttributes {A.caWritingShared = False, A.caReadingShared = False}) inner}
-    <|> do {sOut ; inner <- dataType ; return $ A.ChanEnd A.DirOutput (A.ChanAttributes {A.caWritingShared = False, A.caReadingShared = False}) inner}
+    <|> do {sChannel ; inner <- dataType ; return $ A.Chan (A.ChanAttributes {A.caWritingShared = A.Unshared, A.caReadingShared = A.Unshared}) inner}
+    <|> do {sIn ; inner <- dataType ; return $ A.ChanEnd A.DirInput (A.ChanAttributes {A.caWritingShared = A.Unshared, A.caReadingShared = A.Unshared}) inner}
+    <|> do {sOut ; inner <- dataType ; return $ A.ChanEnd A.DirOutput (A.ChanAttributes {A.caWritingShared = A.Unshared, A.caReadingShared = A.Unshared}) inner}
     <|> do {sLeftQ ; inner <- dataType ; sRightQ ; return $ A.List inner}
     <|> do {(m,n) <- identifier ; return $ A.UserDataType A.Name {A.nameMeta = m, A.nameName = n}}
     <?> "data type"
diff --git a/frontends/ParseRainTest.hs b/frontends/ParseRainTest.hs
index de05751..abfd4df 100644
--- a/frontends/ParseRainTest.hs
+++ b/frontends/ParseRainTest.hs
@@ -531,7 +531,7 @@ testTopLevelDecl =
    passTop (ind, input, exp) = pass (input, RP.topLevelDecl, assertPatternMatch ("testTopLevelDecl " ++ show ind) $ pat $ A.Several m exp)
 
 nonShared :: A.ChanAttributes
-nonShared = A.ChanAttributes { A.caWritingShared = False, A.caReadingShared = False}
+nonShared = A.ChanAttributes { A.caWritingShared = A.Unshared, A.caReadingShared = A.Unshared}
 
 testDataType :: [ParseTest A.Type]
 testDataType =
diff --git a/frontends/RainTypes.hs b/frontends/RainTypes.hs
index 2209220..0a851cc 100644
--- a/frontends/RainTypes.hs
+++ b/frontends/RainTypes.hs
@@ -283,7 +283,7 @@ markCommTypes = checkDepthM2 checkInputOutput checkAltInput
     checkInput :: A.Variable -> A.Variable -> Meta -> a -> RainTypeM ()
     checkInput chanVar destVar m p
       = astTypeOf destVar >>= markUnify chanVar . A.ChanEnd A.DirInput (A.ChanAttributes
-        False False)
+        A.Unshared A.Unshared)
 
     checkWait :: RainTypeCheck A.InputMode
     checkWait (A.InputTimerFor m exp) = markUnify A.Time exp
@@ -299,7 +299,7 @@ markCommTypes = checkDepthM2 checkInputOutput checkAltInput
     checkInputOutput (A.Input _ _ im@(A.InputTimerRead {})) = checkWait im
     checkInputOutput p@(A.Output m chanVar [A.OutExpression m' srcExp])
       = astTypeOf srcExp >>= markUnify chanVar . A.ChanEnd A.DirOutput (A.ChanAttributes
-        False False)
+        A.Unshared A.Unshared)
     checkInputOutput _ = return ()
 
     checkAltInput :: RainTypeCheck A.Alternative