module Main where
 
-- Integer arithmetic with (+) and (/)
data Term = 
      N Int
    | Plus Term Term
    | Div Term Term
 
--
-- Basic evaluator
--
 
eval :: Term -> Int
eval (N n) = n
eval (Plus t1 t2) = eval t1 +     eval t2
eval (Div t1 t2)  = eval t1 `div` eval t2
 
--
-- Evaluator that counts the number of operations
--
 
inc :: Int -> Int
inc n = n + 1
 
evalWithCount :: Term -> (Int, Int)
evalWithCount t = eval' (0, t)
  where
    eval' :: (Int, Term) -> (Int, Int)
    eval' = undefined
    -- The exercise works best if you only use "inc" to bump the accumulator
 
--
-- Evaluator that catches division by zero
--
-- Returns (Ok n) in case of success
-- Returns (Error "Division by zero") otherwise
--
 
data Result a = Error String | Ok a
 
evalChecked :: Term -> Result Int
evalChecked = undefined
 
main = print (undefined::String)

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