[antlr-interest] THelp w/ Tree Grammer - Rule Action Error

[William Koscho]

Hi All,

I have a tree grammar, and am trying to just print out some information from
the tree.  This works fine for matching tokens, but not when matching the
rules.  I'm hoping someone can help explain why this is giving me a
NullPointerException and how to correct it:

Tree Grammar:

// the $i.text causes the NullPointerException, when I $i.text, it works
fine
interfaceDeclaration:  ^(i=interfaceType ID) { System.out.println($i.text +
": " + $ID.text); };

interfaceType:
   PROVIDES
 | REQUIRES;

Corresponding Parser Grammar:

interfaceDeclaration:   interfaceType ID -> ^(interfaceType ID);
interfaceType:
   'provides' -> PROVIDES
 | 'requires' -> REQUIRES;

Thanks very much,
Bill