9. gyakorlat

-- person1

person1 :: (String, String, String, Int)
person1 = ("F.Kány", "ELTE déli tömb","fkany@inf.elte.hu",1 )


-- person2

type Name = String
type Address = String
type Email = String
type Age = Int

person2 :: (Name, Address, Email, Age)
person2 = person1

-- A person1 és a person2 ugyanaz lesz

type Predicate a = a -> Bool

break' :: Predicate a -> [a] -> ([a], [a])
break' p = span (not . p)

data Bool = False | True

data Answer = No | Perhaps | Yes

λ :t No
No :: Answer

λ :t Yes
Yes :: Answer

neg :: Answer -> Answer
neg No      = Yes
neg Perhaps = Perhaps
neg Yes     = No

λ neg Yes
No instance for (Show Answer) arising from a use of ‘print’

-- Derive -> automatikusan implementálja a típusosztályt
λ data Answer = No | Perhaps | Yes deriving Show
λ neg Yes
No

-- instance -> manuálisan implementálható a típusosztály
instance Show Answer where
    -- show :: a -> String
    show No = "No"
    show Perhaps = "Perhaps"
    -- show Perhaps = "Perchance" -- ha így írnánk, akkor `Perchance`-ként használnánk (így fordulna le String-re, ami megjelenik)
    show Yes = "Yes"

instance Eq Answer where
    (==) Yes     Yes     = True
    (==) No      No      = True
    (==) Perhaps Perhaps = True
    (==) _       _       = False

data Complex = C Integer Integer