Matrices in Haskell: 

type Matrix a = [[a]]

i need to create a function: 

compress :: Num a => Matrix a -> Matrix a 

that takes an r-by-c Matrix and returns a new r-by-1 Matrix where the values in each row have been replaced by a length 1 list containing the total value from adding together all the values in that row. For example:

 > compress eg1 [[4],[5],[1],[4]] > compress eg5 [[10.599999999999998],[4.7]] > compress eg3 [[]]

Some examples are:

 -- 4 x 2 matrix eg1 :: Matrix Int eg1 = [ [1, 3], [0, 5], [-3, 4], [2, 2] ] -- 2 x 3 matrix eg2 :: Matrix Int eg2 = [ [3, 1, 4], [-1, 0, 5] ] -- 0 x 0 matrix, an empty matrix eg3 :: Matrix Int eg3 = [ [] ] -- 2x1 matrix eg4 :: Matrix Int eg4 = [ [2], [3] ] eg5 :: Matrix Double eg5 = [ [6.2, 4.3, 7.4, -7.3], [9.3, 1.2, 0.4, -6.2] ]