diff --git a/CSPM-Interpreter.cabal b/CSPM-Interpreter.cabal
--- a/CSPM-Interpreter.cabal
+++ b/CSPM-Interpreter.cabal
@@ -1,5 +1,5 @@
 Name:                CSPM-Interpreter
-Version:             0.3.0.0
+Version:             0.4.0.2
 
 Synopsis:            An interpreter for CSPM
 Description:
@@ -21,7 +21,7 @@
 Extra-source-files:
 Library
   Build-Depends:
-    CSPM-Frontend >= 0.3.0.0
+    CSPM-Frontend >= 0.4 && < 0.5
     ,CSPM-CoreLanguage >= 0.1 && < 0.2
     ,base >= 4.0 && < 5.0
     ,containers >= 0.3 && < 0.4
diff --git a/src/CSPM/Interpreter/Eval.hs b/src/CSPM/Interpreter/Eval.hs
--- a/src/CSPM/Interpreter/Eval.hs
+++ b/src/CSPM/Interpreter/Eval.hs
@@ -41,8 +41,8 @@
 import Data.Digest.Pure.HashMD5 as HashClass
 
 import Control.Arrow
-import qualified Control.Monad.Reader as Reader
-import Control.Monad.RWS.Lazy as RWS hiding (guard)
+import Control.Monad.Reader as Reader
+import Control.Monad.State.Strict
 import Control.Monad hiding (guard)
 import Data.Ord
 import Data.List as List
@@ -50,6 +50,7 @@
 import Data.Set (Set)
 import qualified Data.Map as Map
 import qualified Data.IntMap as IntMap
+import Data.IntMap (IntMap)
 import qualified Data.List as List
 import Debug.Trace
 
@@ -71,31 +72,15 @@
 eval expr = case unLabel expr of
   Var v -> lookupIdent v
   IntExp i -> return $ VInt i
-  SetEnum s -> do
-    l <- mapM eval s
-    return $ VSet $ Set.fromList l
-  ListEnum l -> mapM eval l >>= return . VList
-  SetOpen _  -> throwFeatureNotImplemented "open sets" $ Just $ srcLoc expr
-  ListOpen s -> do
-  -- todo : this can easily give non-termination
-  -- maybe use an enumerator here ?
-    x <- evalInt s
-    return $ VList $ map VInt [x..]
-  SetClose (a,b) -> do
-    s <- evalInt a
-    e <- evalInt b
-    return $ VSet $ Set.fromList $ map VInt [s..e]
-  ListClose (a,b) -> do
-    s <- evalInt a
-    e <- evalInt b
-    return $ VList $ map VInt [s..e]
-  SetComprehension (el,comps) -> do
-    l <- evalSetComp ret comps 
+  SetExp (unLabel -> RangeOpen _ ) _
+    -> throwFeatureNotImplemented "open sets" $ Just $ srcLoc expr
+  SetExp r Nothing -> evalRange r >>= return . VSet . Set.fromList
+  SetExp r (Just comps) -> do
+    l <- evalSetComp ret comps
     return $ VSet l
-    where ret = mapM eval el >>= return . Set.fromList
-  ListComprehension (el, comps) -> do
-    l <- evalListComp (mapM eval el) comps
-    return $ VList l
+    where ret = evalRange r >>= return . Set.fromList
+  ListExp r Nothing -> liftM VList $ evalRange r
+  ListExp r (Just comps) -> liftM VList $ evalListComp (evalRange r) comps
   ClosureComprehension (el, comps) -> do
     l <- evalListComp (mapM eval el) comps
     ClosureSet.mkEventClosure l >>= return . VClosure
@@ -217,6 +202,17 @@
   _ -> throwFeatureNotImplemented "hit catch-all case of eval function"
          $ Just $ srcLoc expr 
 
+evalRange :: LRange -> EM [Value]
+evalRange r = case unLabel r of
+  RangeEnum l -> mapM eval l
+  RangeClosed start end -> do
+    s <- evalInt start
+    e <- evalInt end
+    return $ map VInt [s..e]
+  RangeOpen start -> do
+    s <- evalInt start
+    return $ map VInt [s..]
+  
 evalBool :: LExp -> EM Bool
 evalBool e = do
   v <- eval e
@@ -419,16 +415,17 @@
       y <- switchedOffProc b
       return $ VProcess $ o x y
 
-type DeclM x = RWS (Digest,Env) () (Bindings, IntMap.IntMap Digest) x
- 
+type DeclM x = ReaderT (Digest,Env) (State (Bindings, IntMap Digest)) x
+
 processDeclList :: Digest -> Env -> [LDecl] -> Env
 processDeclList digest oldEnv decls =
--- todo :: really do a lot of testing that we do not end in a loop here
   let
-    ((),(newBinds,newDigests),()) = runRWS action (digest,newEnv) 
-       (getLetBindings oldEnv, letDigests oldEnv)
-    action = mapM_ processDecl decls
-    newEnv = oldEnv { letBindings = newBinds, letDigests = newDigests}
+    (newBinds,newDigests)
+       = execState action' (getLetBindings oldEnv, letDigests oldEnv)
+    action :: DeclM ()
+    action  = mapM_ processDecl decls
+    action' = runReaderT action (digest,newEnv)
+    newEnv  = oldEnv { letBindings = newBinds, letDigests = newDigests}
   in newEnv
 
 bindIdentM :: LIdent -> Value -> DeclM ()
diff --git a/src/CSPM/Interpreter/PatternMatcher.hs b/src/CSPM/Interpreter/PatternMatcher.hs
--- a/src/CSPM/Interpreter/PatternMatcher.hs
+++ b/src/CSPM/Interpreter/PatternMatcher.hs
@@ -64,8 +64,8 @@
 match v             (ConstrSel c) = typeError ("expecting constructor " ++ show c) v
 --  | DotSel Int Int Selector
 
-match (VSet _)      (SingleSetSel _)
-  = throwFeatureNotImplemented "single set pattern" Nothing
+match (VSet s)      (SingleSetSel b)
+  = if not $ Set.null s then match (Set.findMin s) b else failedMatch
 match v             (SingleSetSel _) = typeError "expecting a set" v
 
 match (VSet s)      EmptySetSel