X-Git-Url: https://git.rkrishnan.org/?a=blobdiff_plain;f=hw5%2FCalc.hs;h=46f782018c617ae69a0bb440c77af5a753d1cbed;hb=04036d0605e95c06f5d6dea11c2618267c059550;hp=ef4fd2e2542a1d2ccf8cbb22ed01e335d2f42b74;hpb=305e0c26a007817bb0194358bdb52ad5092e6371;p=yorgey.git

diff --git a/hw5/Calc.hs b/hw5/Calc.hs
index ef4fd2e..46f7820 100644
--- a/hw5/Calc.hs
+++ b/hw5/Calc.hs
@@ -18,3 +18,13 @@ evalStr :: String -> Maybe Integer
 --               Just e -> Just (eval e)
 --              Nothing -> Nothing
 evalStr s = fmap eval (parseExp Lit Add Mul s)
+
+class Expr a where
+  lit :: Integer -> a
+  add :: a -> a -> a
+  mul :: a -> a -> a
+
+instance Expr ExprT where
+  lit = Lit
+  add = Add
+  mul = Mul