LambdaCase

一個句法擴充套件，讓你寫\case 代替\arg -> case arg of。

請考慮以下函式定義：

dayOfTheWeek::Int -> String
dayOfTheWeek 0 = "Sunday"
dayOfTheWeek 1 = "Monday"
dayOfTheWeek 2 = "Tuesday"
dayOfTheWeek 3 = "Wednesday"
dayOfTheWeek 4 = "Thursday"
dayOfTheWeek 5 = "Friday"
dayOfTheWeek 6 = "Saturday"

如果你想避免重複函式名稱，可以編寫如下內容：

dayOfTheWeek::Int -> String
dayOfTheWeek i = case i of
    0 -> "Sunday"
    1 -> "Monday"
    2 -> "Tuesday"
    3 -> "Wednesday"
    4 -> "Thursday"
    5 -> "Friday"
    6 -> "Saturday"

使用 LambdaCase 擴充套件，你可以將其編寫為函式表示式，而無需為引數命名：

{-# LANGUAGE LambdaCase #-}

dayOfTheWeek::Int -> String
dayOfTheWeek = \case
    0 -> "Sunday"
    1 -> "Monday"
    2 -> "Tuesday"
    3 -> "Wednesday"
    4 -> "Thursday"
    5 -> "Friday"
    6 -> "Saturday"