Programming Praxis – Arithmetic Drill

In today’s Programming Praxis exercise, our goal is to write a program that allows children to test their arithmetic skill. Let’s get started, shall we?

First, some imports.

import Control.Monad
import System.Random
import Text.Printf

All we need for a new sum are two random numbers.

drill :: Maybe Int -> IO ()
drill n = play n =<< liftM2 (,) rnd rnd
          where rnd = randomRIO (1, maybe 10 id n)

Processing input isn’t too difficult. Just print the appropriate response and repeat the same sum if the answer is wrong or start a new one when the correct answer is given or requested. Since getLine produces an error when an end-of-file character is encountered we have to use catch to deal with it.

play :: Maybe Int -> (Int, Int) -> IO ()
play n (a,b) = printf "%d + %d = " a b >>
               catch getLine (\_ -> return "quit") >>= \s -> case s of
    "quit" -> putStrLn "Goodbye!"
    "?"    -> print (a + b) >> drill n
    x      -> if x == show (a + b) then putStrLn "Right!" >> drill n
              else putStrLn "Wrong, try again!" >> play n (a,b)

All that’s left to do is to start the program.

main :: IO ()
main = drill Nothing
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