Nils in Sets, and Namespace load: support

[Brian Rice]

(1) Nil in Sets:

A feature that crept into my last alpha post without my intention was a 
patch that I had experimented with for containing Nil elements in Sets. 
It adds one extra slot per Set, but it seems to work. The downside is 
that if you want to play with Nils (which none of the existing Set 
users do), you'll run into problems if you don't just stick with the 
basic operations, add:, remove:, do: (and aggregate methods built on 
it), and includes:.

I may later "optimize" it to lazily allocate the slot when queried. 
There's also a slight tweak which is in the alpha branch but not 
bootstrapped yet which make add: and remove: return Nil instead of the 
containsNil slot value.

Note that our current unit tests do survive this alteration, and 
bootstraps are not impaired, so only code that really makes use of this 
will see an effect. Beware (slightly)!

(2) Namespace-specific loads:

load: got a new keyword, &in:. Alternatively, a Namespace may call 
load: and get the same effect (e.g. "load: 'test' &in: Test" vs. "Test 
load: 'test'"). Basically the parser results are called with 
evaluateIn: that namespace instead of the normal evaluate. There are 
also a couple of things I messed with in namespace.slate. I fixed 
flattened, and added import:from: which just calls addSlot:from:. These 
may get fancier or get more protocols soon.

Note that this use of load: is likely going to cause the parsed code to 
break for various reasons, mostly because we don't have a quick 
facility to generate a distinct but polymorphic variant of the lobby. 
requires:/provides: for example will break, and any other namespaces 
that the code refers to need to be aliased in the one where the loading 
occurs. If your code doesn't do much of this (most code doesn't), it'll 
be easy to adapt the code or the namespace to work together. But it 
sounds like an interesting task for anyone to mess around with (new 
facilities to mock up lobbies). :-)

Enjoy!

--
Brian T. Rice
LOGOS Research and Development
http://tunes.org/~water/