将元组列表转换为列表列表Haskell

Question

我有[("m","n"),("p","q"),("r","s")].我该怎么把它转换成[["m","n"],["p","q"],["r","s"]]？

谁能帮帮我吗？谢谢.

Answer 1

编写单个函数将一对转换为列表:

pairToList :: (a, a) -> [a]
pairToList (x,y) = [x,y]

那你只需要map pairToList:

tuplesToList :: [(a,a)] -> [[a]]
tuplesToList = map pairToList

或者在一行中:

map (\(x,y) -> [x,y])

Answer 2

使用lens你可以简洁地为任意长度的同质元组做到这一点:

import Control.Lens

map (^..each) [("m","n"),("p","q"),("r","s")] -- [["m","n"],["p","q"],["r","s"]]
map (^..each) [(1, 2, 3)] -- [[1, 2, 3]]

请注意,虽然lens图书馆很复杂而且对初学者不友好.

Answer 3

列表理解版本:

[[x,y] | (x,y) <- [("m","n"),("p","q"),("r","s")]]