[antlr-interest] NullPointerException getting text from a rule

[Travis Jensen]

Thanks!  That did it.

tj

On Fri, 2007-11-09 at 16:58 -0800, Curtis Clauson wrote:
> In a tree parser rule action, to use the ".text" attribute with a 
> matched element reference, you must provide the original TokenStream 
> from which the tree was made. If you do not, then input.getTokenStream() 
> will return null and you get that NullPointerException.
> 
> In your main() method, add this line
>      nodes.setTokenStream(tokens);
> after you create the NodeStream.
> 
> This grammar will then work correctly with the "from fred" source text. 
> (tested AntLR v3.0.1)
> 
> -- Curtis
> 
> 
> Travis Jensen wrote:
> > I have the following action associated with my language:
> > 
> > selectStatement   
> >     :    'from' type (localeClause)? (whereClause)?    { 
> > contentType=$type.text; }
> >     ;
> > 
> > If I use "from fred" as input, the rule is matched appropriately, but I 
> > get an NPE when the action is run.  Breaking down the location of the 
> > NPE, I find that my token stream (referenced at "contentType= 
> > input.getTokenStream().toStream(...)") is null.
> > 
> > The very basic driver that I'm using looks like this, which is taken 
> > pretty much verbatim from the ANTLR reference calculator example:
> > 
> > public class Test {
> >     public static void main(String[] args) throws Exception {
> >         // Create an input character stream from standard in
> >         ANTLRInputStream input = new ANTLRInputStream( System.in 
> > <http://System.in>);
> >         // Create an ExprLexer that feeds from that stream
> >         cqlLexer lexer = new cqlLexer(input);
> >         // Create a stream of tokens fed by the lexer
> >         CommonTokenStream tokens = new CommonTokenStream(lexer);
> >         // Create a parser that feeds off the token stream
> >         cqlParser parser = new cqlParser(tokens);
> >         // Begin parsing at rule prog, get return value structure
> >         cqlParser.query_return r= parser.query();
> > 
> >         // Walk the resulting tree
> > 
> >         // Get the tree from the parser
> >         CommonTree t = (CommonTree)r.getTree();
> >         // Create a tree node stream from the resulting tree
> >         CommonTreeNodeStream nodes = new CommonTreeNodeStream(t);
> >         // Create a tree walker
> >         cqlVcm walker = new cqlVcm(nodes);
> >         // launch at the start rule
> >         walker.query();
> >     }
> > }
> > 
> > Just for completeness sake, my entire tree parsing grammar is:
> > 
> > tree grammar cqlVcm;
> > 
> > options {
> >     tokenVocab=cql;
> >     ASTLabelType=CommonTree;
> > }
> > 
> > @header {
> > import java.util.HashMap;
> > import java.util.Map;
> > }
> > 
> > @members {
> > Map attributes = new HashMap();
> > String contentType = null;
> > }
> > 
> > query
> >     :    (expr)+
> >         {
> >         StringBuilder qry=new StringBuilder();
> >         qry.append("select * from ");
> >         qry.append(contentType);
> >         if (attributes.size() > 0)
> >             qry.append(" where");
> >         for (Object key:attributes.keySet())
> >             qry.append(key).append('=').append(attributes.get(key));
> >         System.out.println(qry);
> >         }
> >     ;
> >    
> > expr
> >     :    selectStatement
> >     ;
> >    
> > selectStatement   
> >     :    'from' type (localeClause)? (whereClause)?    { 
> > contentType=$type.text; }
> >     ;
> > 
> > localeClause
> >     :    ^('locale' QUOTED_STRING)            { attributes.put("locale", 
> > $QUOTED_STRING.text); }
> >     ;
> >    
> > whereClause
> >     :    ^('where' whereCompare)
> >     ;
> >    
> > whereCompare
> >     :    ^('=' column QUOTED_STRING)            
> > {attributes.put($column.text, $QUOTED_STRING.text); }
> >     ;
> >    
> > type
> >     :    ID
> >     ;
> > 
> > column
> >     :    ID
> >     ;
> > 
> > Help appreciated. :)
> > 
> > tj
> > -- 
> > Travis Jensen
> > travis.jensen at gmail.com 
> > <mailto:travis.jensen at gmail.com>
> > http://cmssphere.blogspot.com/
> > Software Maven * Philosopher-in-Training * Avenged Nerd
>