Making List of Lists Haskell

Question

i am trying to get pairs of coords and i have got this function that outputs: [9,0,9,1]....... etc

addVal :: Int -> [Int] -> [Int]
 addVal i [] = []
 addVal i (x:xs) =  i:x : addVal i xs

but i want the output to be a list of lists : [[9,0],[9,1]]

addVal :: Int -> [Int] -> [[Int]]
addVal i [] = [[]]

how do i get it so the it will make each pair a list so i i can use it with my other functions to get the smallest of the pairs

Sibi · Accepted Answer · 2015-04-09 10:51:56Z

4

You are almost there, instead of i:x you have to use [i,x]. Note that you want the elements in the new list, so you create [i,x] and pass it up.

addVal :: Int -> [Int] -> [[Int]]
addVal i [] = []
addVal i (x:xs) =  [i,x] : addVal i xs

Demo in ghci

λ> addVal 9 [1,2]
[[9,1],[9,2]]

edited Apr 9, 2015 at 10:51

answered Apr 9, 2015 at 10:46

Sibi

49k18 gold badges105 silver badges172 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

HopefulSplash Over a year ago

thanks i know it was something small but just didnt know it in haskell

Jedai Over a year ago

Note that this is a map : addVal i = map (\x -> [i,x]). I don't know if I would even write a function for this...

HopefulSplash Over a year ago

im trying to convert my java code over to haskell for i can compare them so trying to do it as literal at possible but thanks for the help

Collectives™ on Stack Overflow

Making List of Lists Haskell

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related