Nested cartesian product of Haskell lists

Question

I would like to make a method where I could give it a list of lengths and it would return all combinations of cartesian coordinates up to those lengths. Easier to explain with a

Answer 1

Umm..

cart = sequence . map (enumFromTo 0 . subtract 1)

It's reasonable to expect that a [[a]] -> [[a]] function doing what we expect already exists in the library. So if one is not familiar with sequence, finding it is a simple matter of hoogling it.

Edit: as newacct pointed out:

cart = mapM (enumFromTo 0 . subtract 1)

This can also be found by feeding the previous solution to HLint.