Matrcies in Haskell:

type Matrix a = [[a]]

i need to create a function:

 identity :: Int -> Maybe (Matrix Int) 

that returns the Identity matrix for the given size. An Identity matrix is a square matrix which has zero for all values, except the values on the top-left to bottom-right diagonal which are all one. If the size is less than 1, then the identity matrix isn't defined and Nothing should be returned. For example:

 > identity 2 Just [[1,0],[0,1]] > identity 5 Just [[1,0,0,0,0],[0,1,0,0,0],[0,0,1,0,0],[0,0,0,1,0],[0,0,0,0,1]] > identity 0 Nothing > identity (-1) Nothing