[antlr-interest] Article against TreeWalkers

Terence Parr parrt at cs.usfca.edu
Thu Mar 9 11:40:00 PST 2006

On Mar 9, 2006, at 11:28 AM, Andrew Bell wrote:
>> a : ^(A B) ;
>> is same as
>> a : A DOWN B UP ;
>> if you insert those imaginary navigation nodes, it is just a simple
>> 1D grammar. :)  v3 does this.  Rather a nice generalization, right?
> But aren't you parsing input _text_.



>   Isn't what this is all about?
> What do DOWN and UP do here?  Is there a token in the input called UP
> or DOWN?  You aren't really parsing a tree, you are building a tree.

we're talking about walking a tree here...

> You are parsing a 1-D input and producing a tree output, right?  What
> am I missing here?

This is the tree parser not parser creating trees.  Once you have a  
tree, you need to walk it either by hand or by grammar.  By grammar,  
you can serialize a tree by adding imaginary nodes UP and DOWN that  
encode 2D aspect.  Then you parse normally as a 1D stream of nodes.   
Char, token, tree node...same thing.  a stream of int types to parse :)


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