Update a list of a list of elements in a single list?

Question

I have some code which is designed to replace a value in a list

replaceNth n newVal (x:xs)
 | n == 0 = newVal:xs
 | otherwise = x:replaceNth (n-1) newVal xs
         


        

Answer 1

Using your existing definition:

ghci> let arg = [[3,3,3,3,3],[3,3,3,3,3],[3,3,3,3,3]]
ghci> replaceNth 1 (replaceNth 3 2 (arg !! 1)) arg
[[3,3,3,3,3],[3,3,3,2,3],[3,3,3,3,3]]
ghci> 

To refactor it into a function:

replaceMthNth m n v arg = replaceNth m (replaceNth n v (arg !! m)) arg