On Fri, Feb 20, 2009 at 5:22 AM, Ben Evans
<[email protected]> wrote:
> Hi,
>
> I'm doing some work with JRuby's ast, and I've run into a few questions
> about how the various classes are wired together.
>
> Any hints on the below would be very helpful - I'm making notes as I go and
> would be very happy to polish them for a wiki page or javadoc comments if
> that would be useful.
>
> Apologies if these are covered somewhere on the wiki and I missed it - a
> pointer to docs and instructions to RTF them would be most welcome.
>
> Scoping
> What's the difference between a LocalStaticScope and a BlockStaticScope ?
Scoping
StaticScope represents lexical scoping rules. A BlockStaticScope is a
scope for local variables in a block. A LocalStaticScope is a scope
for local variables not in a block (method body/class body).
So:
def foo(a, c)
[a].each do |b|
proc { d = 1; puts b,c }
end
end
LocalStaticScope(a,c)
BlockStaticScope(b)
BlockStaticScope(d)
The difference between the two scopes is pretty straight-forward. Any
variable resolution in a LocalStaticScope will not check any outer
scopes. A BlockStaticScope will. So in the example above If we
happen to be inside the proc and we are resolving variable 'c', we
will walk out to LocalStaticScope which contains c.
>
> What's the correct way to initialise a top-level static scope - is it:
>
> StaticScope scope = new LocalStaticScope(null);
>
> or something else?
Yep. That is fine. In general it does not matter for
LocalStaticScopes based on my explanation above as to how variables
resolve for scoping. LocalStaticScopes act like top-level scopes in
places that have them.
> Are class and method body scopes considered top-level or should a method
> body scope have the class scope as an enclosing scope? Or does this answer
> depend on closures.
LocalStaticScope is top or local variable scope resolution. We create
these for every scope which is not a block.
> Arguments and Method calls
> How do ArgsNodes work?
>
> What do the special values for restArguments mean (-1 and -2 seem to be
> special somehow) -1 crops up explicitly in a few places and there's a
> boundary test for -2.
-2 was an empty '*' argument. That should be replaced with StarNode now.
-1 represent no rest args.
> What do static and instance methods ArgsNodes look like? Ie, if I was
> calling the ArgsNodes constructor corresponding to a static or an instance
> method, how would this look?
They should look exactly the same. The arguments for the methods are
exactly the same. The only real difference between these two is the
receiver.
>
> Current State
> My current status is that I have a very simple ast (programatically built
> from scratch) which I can feed into the jruby compiler and have it compile
> but the resulting JVM bytecode fails verification - I suspect because I
> don't fully understand ArgsNodes yet, which is causing the verifier's stack
> underflow check to fail.
>
> Btw, is there a way to ask JRuby to just produce an ast from a .rb, output
> it and stop? Or is it just a case of using jdb and a breakpoint?
We have an 'ast' program that will or is shipping with JRuby now:
jruby -S ast source.rb.
This will give you some output.
>
> Thanks,
>
> Ben
>
>
>
>
--
Blog: http://www.bloglines.com/blog/ThomasEEnebo
Email: [email protected] , [email protected]
---------------------------------------------------------------------
To unsubscribe from this list, please visit:
http://xircles.codehaus.org/manage_email
