Immutable and persistent data structures (a la Clojure)

[xiaq]

It would be nice to follow clojure's approach and have immutable data structures by default.

Pros:

1. Facilitates concurrency

2. Avoids the reference vs. value semantics problem; consider the following in Python:

   >>> a = [[1]] * 5
   >>> a
   [[1], [1], [1], [1], [1]]
   >>> a[0][0] = 2
   >>> a
   [[2], [2], [2], [2], [2]]

However, we'd better still have $env and namespaces as mutable maps.

[xiaq]

http://hypirion.com/musings/understanding-persistent-vector-pt-1 is a nice introduction to the Clojure implementation of persistent vectors.

[xiaq]

An implementation of selected persistent data structures was pushed to https://github.com/xiaq/persistent some while ago.

[xiaq]

Abandoned.