[e-lang] Prize and Milestone as mutable state idioms

[Tyler Close]

I've made changes to the discussed JSON writer, based on David's and
Monty's feedback. In the process, I renamed the class, so the current
version is now at:

http://waterken.svn.sourceforge.net/viewvc/waterken/server/trunk/waterken/remote/src/org/waterken/syntax/json/JSONWriter.java?view=markup

I also made the interface public and eliminated its remaining
dependencies, so that the Java file can be downloaded and used on its
own. That wasn't the original goal, but now that so much work has gone
into it, might as well make it generally reusable by others.

On Wed, Jul 2, 2008 at 12:13 PM, David Wagner <daw at cs.berkeley.edu> wrote:
>    Basically, I think there is some invariant among the entire tree of
>    {Value,Object,Array}Writers that are associated with each other: at
>    most one of them can be "active", and calling a method on an inactive
>    one must throw an exception and not modify the state of the tree.
>    Moreover there are certain points in the code that hand off who is
>    "active", and this must only happen at the appropriate points.
>    (Is that right?)  This invariant is tricky to verify.

I haven't yet come up with a way of better expressing this invariant
in code, so I gave up and just wrote a comment explaining how the
invariant is currently enforced. I'm still interested in finding a way
to say this in code, that doesn't require reifying the JSON tree
structure first. I'm not sure if the current pattern is a general
purpose one, but its worth some more thought.

--Tyler