[antlr-interest] Constructing trees and building forests...

Terence Parr parrt at cs.usfca.edu
Thu Jul 29 11:24:26 PDT 2004


On Jul 28, 2004, at 10:43 PM, iank at bearcave.com wrote:

>
>   Ter,
>
>   Thanks for the reply.
>
>   I know that I'm in a minority here, but to me the power of ANTLR is
>   mainly in parser generation, not tree construction.  My views are
>   biased by the fact that most of the parsers I've worked on are for
>   languages like C, Fortran 90, Verilog or VHDL.  In my opinion when
>   you are constructing trees for complex languages, you want to create
>   you own trees.  So I have been largely uninterested in ANTLR's
>   automatic tree construction.

I can understand that for sure.  I usually do a mix since some stuff is 
easy and the AST suffix operators work great.

>   This said, my two cents is for an easy to use, easy to understand,
>   robust parser generator that makes creating parsers for complex
>   languages as easy as possible.  Rather than trees I'd rather have
>   something that makes it easy to understand why the parser generator
>   does not like my grammar.

Yes, i'm working hard on that in my head.  First step was to simply 
reduce the number of grammars that ANTLR couldn't handle; enter 
LL(star).  Unfortunately, when you do get an error it's harder to say 
how/why/where as the input could be arbitrarily long!  I'm thinking 
that I will build up a list of objects with all the info and then 
people can change the reporting behavior with a simple mechanism (just 
walk the list and do something else).  I suspect that an IDE will be 
really important here.  I would like to highlight the paths that are 
ambiguous etc...

>   From my point of view, trees are secondary.  Building trees is not
>   that hard.  Writing parsers by hand is.  So the "juice" provided by
>   ANTLR is that it helps with the most difficult part of parser
>   construction.

The core engine will most definitely focus on this.  Anything else 
could perhaps be a "plugin" :)

>   Of course it's easy for me to say...  Terence, Loring and others are
>   doing all the work.  Those who write the code get to call the
>   shots.  And, as always, I deeply appreciate the work that has gone
>   into ANTLR.

Thanks, as always, for your support, Ian. :)

Terence
--
CS Professor & Grad Director, University of San Francisco
Creator, ANTLR Parser Generator, http://www.antlr.org
Cofounder, http://www.jguru.com
Cofounder, http://www.knowspam.net enjoy email again!
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