Functor example from FP Complete

functor-example.hs

import Safe (readMay)

display maybeAge = 
    case maybeAge of
      Nothing -> putStrLn "Could not read input."
      Just age -> putStrLn $ "In 2020, you will be: " ++ show age

yearToAge age = 2020 - age

main = do
    putStrLn "Please enter your birth year"
    yearString <- getLine
    let maybeAge = fmap yearToAge (readMay yearString)
    display maybeAge