Re: [Jscheme-user] internals questions.

[Ken A. <kan...@bb...>]

At 12:22 PM 7/9/2004 -0400, Geoffrey Knauth wrote:
>On Jul 9, 2004, at 10:36, Ken Anderson wrote:
>>Q1`:
>>In src/jsint/Evaluator.java:
>>public DynamicEnvironment INTERACTION_ENVIRONMENT
>>
>>Should this be static final, or should it be named interactionEnvironment?
>
>Would anyone ever override/replace the interaction environment?
>If yes, I vote the latter.  If no, I vote the former.

Yes, i think it should be an instance field.


>>Q2: analyze()
>>line 265:
>>        return new DynamicVariable((Symbol)x, dynamicEnv);
>>This returns a new DynamicVariable for each use of a symbol in the body.
>>Shouldn't it reuse one if there is one already like Symbol.intern()?  
>>Though that might require a synchronized method.
>
>By DynamicVariable I assume you mean a variable of local scope.  If that is true, then I think you'd want a new one for each new binding, as opposed to each use.  The word "dynamic" is a bit confusing to me, because it means one thing in the context of C or Java, another thing in Common Lisp.  And here we are talking about a Scheme written in Java.
>
>Symbol.intern() -- wouldn't that let you have only one "x", instead of one at the top-level (global scope) and each lower local scope?  Or, in the case of (define x 1) (let ((x 2)) ...), are the two x's guaranteed to have different Symbols, interned separately?

Yes, the name isn't very informative.  
Originally, a Symbol had a name and a value field.  The value was used to store the global value of the Symbol if any.
Several people have contributed code so things are a bit different. A DynamicVariable has a symbol and a DynamicEnvironment which is a hash from symbol -> value.  This is what lets the module system work.

So if you type x to the REPL
The reader returns a the symbol 'x, which the evaluator analyzes and turns into a Dynamic Variable in the evaluator's DynamicEnvironment.  It then executes that DV to produce a value, by looking it up in the DV's DE.

The DV also has a field that is used to store the value during serialization.

This explanation has helped me understand this, and i found a slight bug in serialization and i have a new proposal for DV and DE which i'll send in my next message.

k