x = [3,5,7] primes = 2:x odds = 1:x You can't do sharing like this if your lists are doubly-linked; lots of cool algorithms depend on this sharing.
That constraint makes various other things painful. I suppose there is no one-size-fits-all solution.
Then perhaps it is worth considering having multiple implementations and choosing between them with pragmas and/or command line switches (with a sensible default naturally). Maybe doubly linked lists are not a great idea, but if we had a good implementation with, eg. O(1) access to both ends of the list but poor sharing, we can choose to use it only in cases where queue semantics are important and sharing is not. It would be nice to be able to monkey about with that kind of "under the hood" functionality w/o having to make any code changes. You could also do fun things like have chained-buffer list implementations for [Word8], [Char] etc.