diff --git a/Resolver.hs b/Resolver.hs
--- a/Resolver.hs
+++ b/Resolver.hs
@@ -7,7 +7,7 @@
 import Graph
 import GraphRewriting.Graph
 import GraphRewriting.Graph.Write
-import Control.Monad (liftM, zipWithM, void)
+import Control.Monad (liftM, zipWithM)
 
 
 type Compiler = Rewrite NodeWW
@@ -26,13 +26,13 @@
 	A func arg → do
 		f ← newEdge
 		x ← newEdge
-		void $ newNode Applicator {inp = p, func = f, arg = x}
+		_ ← newNode Applicator {inp = p, func = f, arg = x}
 		compile env f func
 		compile env x arg
 	Λ x e → do
 		b ← newEdge
 		(v, n) ← bindName x
-		void $ newNode Abstractor {name = x, inp = p, body = b, var = v}
+		_ ← newNode Abstractor {name = x, inp = p, body = b, var = v}
 		compile (n : env) b e
 	V var → case env of
 		[  ] → newNode Primitive {inp = p, name = var} >> return ()
@@ -42,7 +42,7 @@
 	L binds e → do
 		(es, names) ← liftM unzip $ mapM bindName (map fst binds)
 		let env' = names ⧺ env
-		void $ zipWithM (compile env') es (Prelude.map snd binds)
+		_ ← zipWithM (compile env') es (Prelude.map snd binds)
 		compile env' p e
 
 bindName ∷ String → Compiler (Edge, Name)
diff --git a/Term.hs b/Term.hs
--- a/Term.hs
+++ b/Term.hs
@@ -6,7 +6,7 @@
 import Text.ParserCombinators.Parsec.IndentParser as Indent
 import Text.ParserCombinators.Parsec.Language
 import Text.ParserCombinators.Parsec.IndentParser.Token
-import Control.Monad (liftM, void)
+import Control.Monad (liftM)
 
 
 data Λ = A Λ Λ            -- ^ application
@@ -31,9 +31,9 @@
 	parenthetic = parens haskell expression
 
 	abstraction = flip label "abstraction" $ do
-		void $ sym "λ" <|> sym "\\"
+		_ ← sym "λ" <|> sym "\\"
 		vars ← many1 ident
-		void $ sym "." <|> sym "→" <|> sym "->"
+		_ ← sym "." <|> sym "→" <|> sym "->"
 		body ← expression
 		return $ foldr Λ body vars
 
diff --git a/graph-rewriting-ww.cabal b/graph-rewriting-ww.cabal
--- a/graph-rewriting-ww.cabal
+++ b/graph-rewriting-ww.cabal
@@ -1,5 +1,5 @@
 Name:           graph-rewriting-ww
-Version:        0.3
+Version:        0.3.1
 Copyright:      (c) 2010, Jan Rochel
 License:        BSD3
 License-File:   LICENSE
@@ -17,7 +17,7 @@
 Executable ww
   Main-Is:        Main.hs
   Build-Depends:
-    base >= 4.3 && < 4.6,
+    base >= 4 && < 4.6,
     base-unicode-symbols >= 0.2 && < 0.3,
     graph-rewriting >= 0.7 && < 0.8,
     graph-rewriting-layout >= 0.5.1 && < 0.6,