I have problems trying to separate a list follows, suppose we have the following lists

[[1,2,3,4], [5,6,7,8], [9,10,11,12 ], [13,14,15,16,17]].

The result should be:

[[1,5,9,13] [2,6,10,14] [3,7,11,16] [4,8,12,16]]

I'm trying to do it the following way:

joinHead (x: xs) = map head (x: xs)
separateLists (x: xs) = xs joinHead x ++ separateLists

obviously this does not work. I hope you can help me. thx.