Move Num instance around a little.

HW1.fedorind.hs

@@ -16,11 +16,6 @@ data Expr
    | Mul Expr Expr   -- ^ Multiplication expressions
   deriving (Eq,Show)
 
-instance Num Expr where
-    (+) = Add
-    (*) = Mul
-    fromInteger = Lit . fromInteger
-
 fold :: (Int -> a) -> (a -> a -> a) -> (a -> a -> a) -> Expr -> a
 fold f1 f2 f3 = rec
     where 
@@ -28,6 +23,11 @@ fold f1 f2 f3 = rec
         rec (Add l r) = f2 (rec l) (rec r)
         rec (Mul l r) = f3 (rec l) (rec r)
 
+instance Num Expr where
+    (+) = Add
+    (*) = Mul
+    fromInteger = Lit . fromInteger
+
 -- | The expression: 2 + 3 * 4
 e1 :: Expr
 e1 = Add (Lit 2) (Mul (Lit 3) (Lit 4))