http://atnd.org/events/36770

1. すごい Haskell 読書会
in 大阪
#5
岡本和樹
@kakkun61

2. 7.1 新しいデータ型を定義する
• data Bool = True | False
• data 型 = 値コンストラクター

3. 7.2 形づくる
• 円
– x座標
– y座標
– 半径
• 四角形
– 左上x座標
– 左上y座標
– 右下x座標
– 右下y座標

4. 7.2 形づくる
• data Shape =
Circle Float Float Float |
Rectangle Float Float Float Float
• Circle :: Float -> Float -> Float ->
Shape
• Rectangle :: Float -> Float -> Float ->
Float -> Shape

5. 7.2 形づくる
• area :: Shape -> Float
• area (Circle _ _ r) = pi * r ^ 2
• area (Rectangle x1 y1 x2 y2) =
(abs $ x1 - x2) * (abs $ y1 - y2)

6. 7.2 形づくる
• data Point =
Point Float Float deriving (Show)
• data Shape = Circle Point Float |
Rectangle Point Point
deriving (Show)
• area :: Shape -> Float
• area (Circle _ r) = pi * r ^ 2
• area (Rectangle (Point x1 y1) (Point x2
y2)) = …

7. 7.3 レコード構文
• data Car =
Car String String Int
deriving (Show)
• Car "Ford" "Mustang" 1967

8. 7.3 レコード構文
• data Car =
Car String String Int
deriving (Show)
• company :: Car -> String
• company (Car company _ _) = company
• model :: Car -> String
• model (Car _ model _) = model
• year :: Car -> Int
• year (Car _ _ year) = year

9. 7.3 レコード構文
• data Car =
Car { company :: String
, model :: String
, year :: Int
} deriving (Show)
• Car {year = 1990, model = "Mark
II", company = "Toyota"}
• Car "Ford" "Mustang" 1967

10. 7.4 型引数
• data Maybe a = Nothing | Just a
• Just “Hay” :: Maybe String
• [1..10] :: [Int]
• [“learn”, “Haskell”] :: [String]

11. 7.4 型引数
• Map k v
• data (Ord k) => Map k v ...
• データ宣言には決して型クラス制約をつ
けない
• Map.toList :: Map k v -> [(k, v)]

12. 7.4 型引数
• data Vector a = Vector a a a
deriving (Show)
• vplus :: (Num t) => Vector t ->
Vector t -> Vector t
• (Vector i j k) `vplus` (Vector l m
n) =
Vector (i+l) (j+m) (k+n)
• vectMult :: (Num t) => Vector t -> t
-> Vector t
• scalarMult :: (Num t) => Vector t ->
Vector t -> t

13. 7.5 インスタンスの自動導出
• data Person = Person
{ firstName :: String
, lastName :: String
, age :: Int
} deriving (Eq)

14. 7.5 インスタンスの自動導出
• deriving (Eq, Show, Read)
• show :: Person -> String
• read :: String -> Person

15. 7.5 インスタンスの自動導出
• ghci> read "Person {firstName
=¥"Michael¥", lastName
=¥"Diamond¥", age = 43}" :: Person
• Person {firstName = "Michael",
lastName = "Diamond", age = 43}

16. 7.5 インスタンスの自動導出
• data Bool =
False | True deriving (Ord)
• ghci> True `compare` False
• GT
• ghci> False < True
• True

17. 7.5 インスタンスの自動導出
• data Day =
Monday | Tuesday | Wednesday |
Thursday | Friday | Saturday |
Sunday
deriving ( Eq, Ord, Show, Read
, Bounded, Enum)

18. 7.5 インスタンスの自動導出
• Bounded クラス
• ghci> minBound :: Day
• Monday
• ghci> maxBound :: Day
• Sunday

19. 7.5 インスタンスの自動導出
• Enum クラス
• ghci> succ Monday
• Tuesday
• ghci> pred Saturday
• Friday
• ghci> [Thursday .. Sunday]
• [Thursday,Friday,Saturday,Sunday]

20. 7.6 型シノニム
• type String = [Char]
• type AssocList k v = [(k, v)]
• data Either a b = Left a | Right b
deriving (Eq, Ord, Read, Show)