Struggling with lists of lists in Haskell

Question

Can anybody help me with this function?

 getCell :: [[Int]] -> Int -> Int -> Int  

Where m i j are the indexes of the lines and the c

Answer 1

Just for fun - one liner

getCell l i j = (((l ++ repeat []) !! i) ++ repeat (-1)) !! j 

Answer 2

This should work using the (!!) operator. First check if index is in the list, then access the element at that index using (!!).

getCell m i j = if i >= length m then -1
                else let
                         m0 = m !! i
                     in if j >= length m0 then -1
                        else m0 !! j