HaskellのRecord

HaskellのRecord

code:hs

data 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

code:hs

data 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

code:hs

foo1 = Foo { baz = 1 }

code:hs

update :: Foo -> Int -> Foo

update foo newId = foo { baz = newId }

code:hs

patt = \case

Foo { baz = 1 } -> ...

...

code:hs

get :: Foo -> Int

get = baz