Convert List of Tuples to List of Lists Haskell

问题

I have [("m","n"),("p","q"),("r","s")]. How can I convert it to [["m","n"],["p","q"],["r","s"]]?

Can anyone please help me? Thanks.

回答1:

Write a single function to convert a pair to a list:

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

Then you only have to map pairToList:

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

Or in a single line:

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

回答2:

Using lens you can do this succinctly for arbitrary length homogenous tuples:

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]]

Note though that the lens library is complex and rather beginner-unfriendly.

回答3:

List comprehension version:

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

来源：https://stackoverflow.com/questions/20449231/convert-list-of-tuples-to-list-of-lists-haskell