laundryCoins.hs

laundryCoins.hs

#!/usr/bin/env runhaskell
module Main where

data Coin = Quarter | Loonie deriving (Eq, Show)

type Cents = Int

cents :: Coin -> Cents
cents Quarter = 25
cents Loonie  = 100

cycleCost :: [Coin]
cycleCost = concat . replicate 2 $ [Quarter, Quarter, Loonie]

nDaysCost :: Int -> [Coin]
nDaysCost n = foldr (++) [] $ replicate n cycleCost

sumCost :: [Coin] -> Cents
sumCost = foldr (+) 0 . map cents

loonies :: [Coin] -> Int
loonies = length . filter (==Loonie)

quarters :: [Coin] -> Int
quarters = length . filter (==Quarter)

showCoinsNeeded :: Int -> String
showCoinsNeeded n = "To do laundry " ++ show n ++ " times, ask the cashier for:\n" ++ show l ++ " loonies,\n" ++ show q ++ " quarters, from\n$" ++ show t ++ " cash back" where
  cost = nDaysCost n
  l = loonies cost
  q = quarters cost
  t = (sumCost cost) `div` 100  -- For our case, cycle costs rounds to dollars, so we ignore the mod.

main :: IO ()
main = putStrLn $ showCoinsNeeded 3