[antlr-interest] Runtime code question - v3 ea4

[Terence Parr]

On Jul 11, 2005, at 11:18 AM, Gary Evans wrote:

> Folks,
>
> I have been studying the code in the runtime in order to translate  
> it to another language,

Hi Gary!  Nice to have you here.  Thanks for the questions.

First thing: within a few weeks I hope to refactor the Java.stg  
template file to be much smaller and easier to maintain, which would  
necessitate a change to your templates (well, if you wanted to say  
"similar").

>   and I have a question about a couple of the classes:   
> ANTLRFileStream and  ANTLRStringStream.  Just a quick note - I am  
> not a real programmer, and I am just now  learning about java, so I  
> may have completely missed the boat here (so please be kind if   
> this is the case).

Yeah, I wanted to revisit those class names and functionality at some  
point, so please critique away!

> Within these classes is a method called "public int mark()".  It  
> looks like a useless  method since all it does is create a  
> CharStreamState object, give it the data from .p,  .line,  
> and .charPositionInLine, and then it just returns 0!

Excellent observation.  It turns out that there can only be one mark  
"location" in the current implementation; hence the marker number is  
always 0.  Later, when I add in syntactic predicates, we will need to  
make this more general.  For now, I opted for a more efficient  
implementation.

> Shouldn't it do something more, like save that state back into the  
> variable markers?

It saves it into a variable (an array of size 1) and then reuses it  
in rewrite(m) where m is always 0.

> If not, then what method does save data into markers?  All I can  
> see is that when the  object is initialized, it saves a blank  
> CharStreamState into markers.  After that, I don't  see anything  
> that puts more information into markers, so what is its purpose?
>
> Also, rewind() gives us the ability to go to a particular mark  
> within markers and set the  local variables to those values - but I  
> cannot figure out where we ever set any information  in markers.

The marker is set in mark() and the instance variables are wacked and  
reset to the marker in rewind() :)

> FYI - I am looking at the code for antlr v3 ea4 (I think).  I  
> clicked on a link to download  version ea5, but the name of the  
> file that was actually downloaded was ea4.

That's pretty odd...sounds like a browser issue.  What does  
Tool.VERSION reveal?

Ter
--
CS Professor & Grad Director, University of San Francisco
Creator, ANTLR Parser Generator, http://www.antlr.org
Cofounder, http://www.jguru.com