Ticket.hs

{-# LANGUAGE OverloadedStrings #-}

module Main where

import Data.Text ( Text )

type Name = Text
type Age  = Int
type Citizenship = Text
type GoalCountry = Text

data Ticket = Ticket
    { customerFullName      :: Name
    , customerAge           :: Age
    , customerCitizenship   :: Citizenship
    , customerGoalCountry   :: GoalCountry
    , additionalInfo        :: TicketAdditionalInfo
    }

data TicketAdditionalInfo = TicketAdditionalInfo
    { visaRequired :: Bool
    }

orderTicket :: Name -> Age -> Citizenship -> GoalCountry -> Maybe Ticket
orderTicket fullName age citizenship goalCountry = maybeTicket
  where
    maybeTicket = 
        if custorerIsEnoughOld
            then Just ticket
            else Nothing

    ticket = Ticket { customerFullName      = fullName
                    , customerAge           = age
                    , customerCitizenship   = citizenship
                    , customerGoalCountry   = goalCountry
                    , additionalInfo        = addInfo
                    }

    addInfo = TicketAdditionalInfo { visaRequired = checkGoalCountry
                                   }

    custorerIsEnoughOld :: Bool
    custorerIsEnoughOld = age >= 18

    checkGoalCountry :: Bool
    checkGoalCountry = goalCountry == "USA"

main :: IO ()
main = putStrLn $ do
    let ticketBox = orderTicket "Denis Shevchenko" 36 "Russia" "Armenia"
    case ticketBox of
        Nothing     -> "Sorry, your ticket is gone!"
        Just ticket ->
            if visaRequired . additionalInfo $ ticket
                then "Sorry, you need visa to visit this country."
                else "Hey yo! Welcome to our country!"