[antlr-interest] ANTLR 3.0 question about common actions

[Terence Parr]

Howdy,

We have an interesting problem to solve for the ANTLR 3.0 regarding 
multiple target languages and free-form actions.  I'd like your help.

There are two problems with the existing ANTLR regarding 
actions/targets.  A grammar built for one language has to be manually 
updated to work for another output target.  In other words, tree 
construction for C++ won't work with C# or Java as a back-end.  You 
have to update it if you have any actions other than the ^ and ! AST 
operators in your grammar.

Further, think about all the $setType and newline() nonsense in the 
lexer.  Each target may have different requirements so actions must 
have a special parser etc... to handle actions.  Yuck.

For the common things like symbol table management, AST construction, 
and lexer actions, I propose a standard syntax that can easily be 
translated to a target language.  The only issue is, how do you handle 
conditional code execution?  For example, you only want to set the 
token type in a lexer rule upon some complicated expression that you 
want to express in the target language?

So, the main question is: how can we make standard actions in order to 
avoid retargeting issues and yet allow for free-form actions, 
especially those that predicate standard actions?

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