Marek Kubica <ma...@xivilization.net> writes: > > I guess if it is functional then every mutation must copy and return a > > new data structure?
Yes. > > (Which will be much more efficient in Haskell than > > in Python - Haskell can share most of the underlying data whereas Python > > would have to create a new dict every time. At least it only stores > > references.) The structure sharing is essential, but you can do it in Python, just not using Python dicts as far as I can tell. > Who says that it must create a whole new one? I could imagine that with a > bit weakref code and some thought an immutable dictionary that shares > data would be possible in Python too. I don't see a way to do that. Suppose d and e are dicts that are supposed to share structure except d['name']='bob' and e['name']='joe'. How do weakrefs help? Functional dictionaries are usually implemented using red-black trees or AVL trees or similar data structures, rather than hash tables. -- http://mail.python.org/mailman/listinfo/python-list
