Fun with View Patterns: Calculate bonus points for a customer based on their reward status

View_Patterns_Demo.hs

{-# LANGUAGE ViewPatterns #-}

module Main where

data Status = Silver 
            | Gold 
            | Platinum 
            deriving (Show)

type Points = Int

data Customer = Customer { name   :: String
           		 , points :: Points
           		 , status :: Status
           		 } deriving (Show)

bonusPoints :: Customer -> Points
bonusPoints c@(status -> Silver)   = points c * 10
bonusPoints c@(status -> Gold)     = points c * 100
bonusPoints c@(status -> Platinum) = points c * 1000
bonusPoints _ = 0

main :: IO ()
main = do
  putStrLn "\n\tFun with View Patterns\n"

  let bob = Customer "Bob" 10 Silver
      joe = Customer "Joe" 10 Gold
      ann = Customer "Ann" 10 Platinum

  print $ bonusPoints bob
  print $ bonusPoints joe
  print $ bonusPoints ann
  
{-
	Fun with View Patterns

100
1000
10000
-}