HaskellのRecord
HaskellのRecord
hsdata User = User
{ userId :: Int
, name :: String
, age :: Int
}
let user = User { userId = 3, name = "tarou", age = 28 }
name user -- > "tarou"
// update
let changeName = user { name = "hanako" } -- > { userId = 3, name = "hanako", age = 28}Record型を定義すると同時に色々なものが暗黙的に導入される
hsdata Foo = FooC { baz :: Int } このような型を定義すると以下のものが導入される
① 型
Foo ② Constructor
Fooc ③ 構築の為の
baz hsfoo1 = Foo { baz = 1 }④ 更新の為の
baz hsupdate :: Foo -> Int -> Foo
update foo newId = foo { baz = newId }これって、言語的には③と同じなのかな
⑤パターンマッチの為の
baz hspatt = \case
Foo { baz = 1 } -> ...
...⑥ getterの為の
baz hsget :: Foo -> Int
get = bazhttps://exploring-better-ways.bellroy.com/the-unreasonable-effectiveness-of-polymorphic-records.html