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| -rw-r--r-- | lec05/Calc.hs | 17 |
1 files changed, 16 insertions, 1 deletions
diff --git a/lec05/Calc.hs b/lec05/Calc.hs index cd6f408..f97d784 100644 --- a/lec05/Calc.hs +++ b/lec05/Calc.hs @@ -15,4 +15,19 @@ eval (Mul l r) = eval l * eval r evalStr :: String -> Maybe Integer evalStr s = case parseExp Lit Add Mul s of Nothing -> Nothing - Just t -> Just (eval t) + Just t -> Just (eval t) + +-- Exercise 3 + +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 + +reify :: ExprT -> ExprT +reify = id |