Extra functions for lists

takeWhileLen, applied to a predicate f and a list xs, returns the longest prefix (possibly empty) of xs of elements that satisfy f and the length of the list taken. The time complexity of this function is equivalent to takeWhile.

splitAtLen, simmilar to splitAt but also returns the length of the splited list.

Almost the same as span, but returns the number of elements in the list that satisfy f at the same time.

lastInit returns Just (init xxs) when f (last x) == True for then given list xxs. Otherwise, returns Nothing