[antlr-interest] ANTLR v3 Syntax Questions: !, [squareBrackets]; Tree Building

[Randall R Schulz]

Hi,

In reviewing the v3 examples I noticed this (from 
the "examples-v3/simplecTreeParser/simplec.g" example):

stat: forStat
    | expr ';'!
    | block
    | assignStat ';'!
    | ';'!
    ;


What do the trailing exclamation points mean?


-==--==--==--==--==--==--==--==--==--==--==--==--==--==--==-

In the slide show at 
<http://www.antlr.org/workshop/ANTLR2005/presentations/ANTLR-v3.ppt> 
there are some snippets of ANTLR v3 rules that look like this:

a[String s] returns [float y]
  : id=ID f==field (ids+=ID)+
    {$s, $y, $id, $id.text, $f.z; $ids.size();}
  ;

field returns [int x, int z] : ... ;


How are these rules (or fragments thereof) interpreted?

I'm also wondering how these features, which I gather have something to 
do with the results or return value from a given rule activation, 
relate to or interact with the tree-building constructs that are 
specified using the "-> ..." notation. Are the constructs shown in the 
example above allowed with the grammar option "output = AST;"?


Thanks.

Randall Schulz