fake.hs

data Form = Form
  { username :: String
  , password :: String
  , gravatar :: Image}
  
validate :: Form -> Maybe a
oneEach, fileType, minLength :: Validator
  
main = do
  user <- validate Form <$> minLength 8 username 
                        <*> oneEach [character, number, special] password
                        <*> fileType JPEG gravatar
  case user of 
    (Just u) -> redirect welcomePage
    Nothing -> redirect loginPage