[antlr-interest] Custom AST nodes - attempt #2

[Bill Andersen]

Hi Ter

I set ASTLabelType = ASNode in options on the tree grammar

Got runtime cast error

Exception in thread "main" java.lang.ClassCastException: org.antlr.runtime.tree.CommonTree cannot be cast to com.hf.lang.eclif.ltt.ASNode

 in generated code:

            // /Users/bill/Documents/Eclipse Workspaces/workspace2/OWExperimental/LTT2/com/hf/lang/eclif/ltt/ASPass1.g:21:4: ^( AS_SPEC ( rule )+ )
            {
            root_0 = (ASNode)adaptor.nil();

I get what's going on in ANTLR - the default adaptor is spitting out CommonTree instances.  This seems to imply that one has to supply a custom adaptor.  Is this true?

WIth no adaptor and with ASTLabelType = CommonTree the tree grammar works just fine - with no actions.

Now, when I try to access a node in an action in a tree grammar as an ASNode, I can only get it to work with an explicit cast in the semantic action

simple_alt
	: AS_TYPE
   	{ System.out.println( ">>> " + ((ASNode) $AS_TYPE).nodeType ); }
	| ^(AS_SUBRULE ID)
	;

Is this the verdict?  Either write an adaptor that does the right thing or live with the casts?

On Jul 22, 2010, at 16:34 , Terence Parr wrote:

> Hi Bill. try setting ASTLabelType in tree grammar.
> T
> On Jul 22, 2010, at 12:26 PM, Bill Andersen wrote:
> 
>> Hi Folks,
>> 
>> This is my second attempt at asking this question.  Hopefully it is clear.  If not, please let me know.
>> 
>> I'm interested in using a custom AST node class to carry type information.
>> 
>> I do not want to build a custom TreeAdaptor to determine node type based on token id because only a few AST nodes will have to be of the custom class.
>> 
>> Here's a sample production from the tree generating grammar.
>> 
>> rule
>> 	: ... match something ...
>> 	-> ^(NODE<CustomType>[param] ...)
>> 	;
>> 
>> So far so good.  I know how to do this.  
>> 
>> Let's say CustomType looks like this
>> 
>> class CustomType extends CommonTree {
>> 	public T param;
>> 	public CustomType(int ttype, T param) { ... }
>> 	public T getParam() { ... }
>> 	...
>> }
>> 
>> Now I have another grammar that consumes ASTs from the first grammar.  I want to do this:
>> 
>> rule
>> 	: ^(NODE ...)
>> 	  { ... do something with this information ... }
>> 	;
>> 
>> So, what syntax do I need in the action to get a T-typed param value from this node?
>> 
>> Any help appreciated 
>> 
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>