diff --git a/Graphics/Diagrams/FunctionGraphs.hs b/Graphics/Diagrams/FunctionGraphs.hs
--- a/Graphics/Diagrams/FunctionGraphs.hs
+++ b/Graphics/Diagrams/FunctionGraphs.hs
@@ -55,17 +55,15 @@
 
 -- | Display an arc given by a function.
 displayArc
-    :: (Fractional a, Real b) 
+    :: (Fractional a, Real b, Real c) 
     => Point                -- ^ display area left-bottom corner
     -> Point                -- ^ display area right-up corner
     -> (Double, Double)     -- ^ parameter interval
-    -> (a -> (b, b))        -- ^ arc on the plain
+    -> (a -> (b, c))        -- ^ arc on the plain
     -> Diagram
 displayArc a b (k1,k2) f 
-    = withCoords a b $ joinPoints (arcPoints int f)
-  where
-    arcPoints (k1,k2) f
-        = [ (realToFrac x, realToFrac y)
+    = withCoords a b $ joinPoints
+          [ (realToFrac x, realToFrac y)
           | t <- [k1-0.1, k1.. k2+0.1]
           , let (x, y) = f (realToFrac t) ]
 
diff --git a/dia-functions.cabal b/dia-functions.cabal
--- a/dia-functions.cabal
+++ b/dia-functions.cabal
@@ -1,5 +1,5 @@
 name:                dia-functions
-version:             0.2
+version:             0.2.1
 category:            Graphics, Education
 synopsis:            An EDSL for teaching Haskell with diagrams - functions
 description: