Re-use a fold because Parisa may not have my HW1 file.

HW2.fedorind.hs

@@ -5,8 +5,8 @@ module HW2 where
 import HW1
 
 -- Copied from my HW1 for your convenience!
-fold :: (Int -> a) -> (a -> a -> a) -> (a -> a -> a) -> Expr -> a
-fold f1 f2 f3 = rec
+fold' :: (Int -> a) -> (a -> a -> a) -> (a -> a -> a) -> Expr -> a
+fold' f1 f2 f3 = rec
     where 
         rec (Lit i) = f1 i
         rec (Add l r) = f2 (rec l) (rec r)
@@ -35,7 +35,7 @@ fold f1 f2 f3 = rec
 --   True
 --   
 toRPN :: Expr -> String
-toRPN = fold show (rpn "+") (rpn "*")
+toRPN = fold' show (rpn "+") (rpn "*")
     where rpn op l r = concat [l, " ", r, " ", op]
 
 
@@ -82,7 +82,7 @@ fromRPN = head . foldl step [] . words
 --   >>> eval (neg e2)
 --   -65
 --
-neg = fold (Lit . negate) Add (Mul . neg) -- Not efficient, but short :^)
+neg = fold' (Lit . negate) Add (Mul . neg) -- Not efficient, but short :^)
 
 
 -- | Takes two expressions and returns an expression that evalautes to the