[antlr-interest] Selectively suppressing tree output

[David Smith]

I'm trying to parse an if statement of this form:
if a > b
     a = b + 1
elseif a < b
     b = a - b
     c = 42
     d = 4
else
     b = 4
     c = a - b
end

... using the following grammar snippet:

prog:   body EOF!
         ;

body    :
         ( (stat  {if($stat.tree!=null)
                System.out.println($stat.tree.toStringTree());}
         | ifStat) {if($ifStat.tree!=null)
                System.out.println($ifStat.tree.toStringTree());} )*
         ;

stat:
         (ID GETS) => ID GETS expr NEWLINE -> ^(GETS ID expr)
     |   expr NEWLINE        -> expr
     |    NEWLINE             ->
     ;

ifStat
     : IF^ expr body
       (ELSEIF expr body)*
       (ELSE body)?
       END
     ;

... Amazingly enough, it's trying to work but with the following very 
odd behavior.  the tree output is like this:
(= a (+ b 1))
(= b (- a b))
(= c 42)
(= d 4)
(= b 4)
(= c (- a b))
(if (> a b) (= a (+ b 1)) elseif (< a b) (= b (- a b)) (= c 42) (= d 
4) else (= b 4) (= c (- a b)) end)

... It seems to be putting all the body statements into the tree and 
then putting them "correctly" into the (if ...) node.
Furthermore, if i have comments after the if statement, the (if ...) 
node is repeated for each comment.

Is there a way to suppress unwanted tree output?

                                 DMS


David M. Smith http://www.cc.gatech.edu/fac/David.Smith
Georgia Institute of Technology, College of Computing
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