[antlr-interest] Composing tree grammars

[Sam Harwell]

Hi Andreas,

 

Make the actions in your tree grammar call virtual/abstract functions. Then derive a new all-code class from the tree grammar class that overrides those functions to provide the action implementation. The ANTLR Tool itself uses this pattern in the AssignTokenTypesWalker tree grammar.

 

Sam

 

From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-bounces at antlr.org] On Behalf Of Andreas Meyer
Sent: Friday, February 06, 2009 1:01 PM
To: antlr-interest at antlr.org
Subject: [antlr-interest] Composing tree grammars

 

Hi!

 

I am using ANTLR 3.1 and I want to compose tree grammars in a way, that I have one "base" grammar that contains all rules, in order to define a traversal, but without actions/rewrites. Then, a second grammar imports the "base" grammar, and overrides only some rules. Now, if I try to use the second grammar on the input, the ANTLR runtimes complain about mismatched input: it seems that internally, the walker does not consume enough tokens, so that it expects the tokens "behind" the current token. FYI, I used the java/simplecTreeWalker example from the antlr 3.1 distribution and basically copied the walker, spelled "import ..." and removed all but one rule from the copy.

 

Did I use composite tree grammars in a wrong way? If so, how can I define multiple tree grammars for only small parts of the grammar?

Andreas Meyer
Developer
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