[antlr-interest] Re: trees with payloads??

[John D. Mitchell]

>>>>> "lgcraymer" == lgcraymer  <lgc at mail1.jpl.nasa.gov> writes:
>>>>>> In antlr-interest at yahoogroups.com, "John D. Mitchell"
[...]

>> IMNSHO, the dynamic attributes support is a fundamental feature of
>> Antlr v3.

> Well, maybe.  It is a feature that has not yet been put to experimental
> test.  It might turn out to be extremely valuable, or it might be just
> another bit of glitz.

It's more than just glitz.

Coming from a language designer's perspective, dynamically scoped
attributes fill a capability niche that is not provided for by any of the
statically scope capabilities.

In terms of praxis, look at how many times people have written their own
(buggy :-) version of dynamic attributes.  Heck, I've done it a handful of
times myself on different translation projects.


> Also, while Hashmaps might be required by ANTLR to support dynamic
> attributes, that does not mean that they should be present in the
> generated code.  Generating attribute classes or structures should be
> pretty straightforward, and the runtime attribute containers should
> probably be implemented as fields in the generated lexers, parsers, and
> treewalkers so that they are accessible within rules.  That would
> certainly help to ensure that analysis passes (most of the work done in
> actions) can have good performance.  And the ANTLR 3 output templates
> should make the code generation even easier.

Again, in terms of implementation, I'm extremely open to allowing the
different code generators & runtime combinations to do whatever they want
as long as they provide all of the capabilities.

As I noted for the notes from the workshop, the dynamically scoped
attributes need to support cabilities for things like LIFO & FIFO access;
specification of things like at most one/n, exactly one/n, at least one/n;
pushing/popping bundles of attributes; search current scope for attribute,
search up stack for attribute; etc.

Take care,
	John


 
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