maybe-result.elm

type Maybe a
    = Just a
    | Nothing


-- Partial Functions

-- toFloat : String -> Maybe Float
a =
    String.toFloat "123"
-- Just 123.0


b =
    String.toFloat "-42"
-- Just -42.0

c =
    String.toFloat "31a"
-- Nothing



-- List.head : List a -> Maybe a
d =
    List.head [ 1, 2, 3 ]
-- Just 1


e =
    List.head []
-- Nothing

numbers : List Int
-- filterMap : (a -> Maybe b) -> List a -> List b
numbers =
    List.filterMap String.toInt [ "3", "hi", "12", "4th", "May" ]
-- numbers == [3, 12]



-- Optional Fields

type alias User =
    { name : String
    , age : Maybe Int
    }


sue : User
sue =
    { name = "Sue", age = Nothing }


tom : User
tom =
    { name = "Tom", age = Just 24 }


canBuyAlcohol : User -> Bool
canBuyAlcohol user =
    case user.age of
        Nothing ->
            False

        Just age ->
            age >= 21


type Result error value
    = Ok value
    | Err error


type Error
    = BadUrl String
    | Timeout
    | NetworkError
    | BadStatus Int
    | BadBody String