Haskell nested lists

Question

I'm new to haskell programming and I'm trying to check if the diagonally adjacent elements in the nested lists are not negative of each other. I have my function as:

checkNegation :: [[Int]] -> Bool

Example: checkNegation[[1,2], [3, -1]] will return False checkNegation [[1,2],[-1,3]] will return True.

Answer 1

I would suggest breaking the problem into steps.

Step 1: Write a function to get the diagonal elements:

diag :: [[a]] -> [a]

You may find this question helpful.

Step 2: You'd like to check if the adjacent elements of the resulting list are negatives of each other:

allAdjNeg :: [Int] -> Bool

where allAdjNeg [-1,1,-1,1] = True.

This, too, might be most easily done in steps. In step 2(a), check each pair of adjacent elements. You may be able to adapt the answer to this question to write a function:

adjNeg :: [Int] -> [Bool]

Hint: If you define a function isNeg x y = x == -y, this is a binary operator just like (-) and can be used with zipWith in the same way.

In step 2(b), you want to see if the list [Bool] returned by adjNeg is all-True. The and :: [Bool] -> Bool function will be helpful here. That should allow you to define allAdjNeg.

Then, your final function will be something like:

checkNegation :: [[Int]] -> Bool
checkNegation lsts = not (allAdjNeg (diag lsts))