[antlr-interest] I'm stuck with my parser tree generator ..

[whaefelinger]

I do not get the picture about this parser trees and how to utilitze 
them. Here's my very simple problem: 

My parser should accept a list of (simple) expressions, for
example:

 5+4 ; 3*2; 

My parser should then further evaluate each expression in the
list and summarize  them up. So my input 5+4 ;3*2; should end
up in printing 15.

Here's my Parser:

 class CalcParser extends Parser;
  options { buildAST = true; }

  tokens { EXPR; }

  stmts
    :  ( 
            expr {
                // tree construction rule here?
            } 
            ";"!
        )+ 
    ;

  expr
    :	INT ((PLUS^|MULT^) INT)*
    ;


and this is my tree parser:

 class CalcTreeWalker extends TreeParser;

 stmts returns [float r]
 { 
    float a = 0;
    r = 0; 
 }
    : #(EXPR a=expr) { r+=a ; } 
    ;

 expr returns [float r]
 {
	float a,b;
	r=0;
 }
    :	#(PLUS  a=expr b=expr) { r = a+b; }
    |   #(MULT  a=expr b=expr) { r = a*b; }
    |	i:INT	{r = (float)Integer.parseInt(i.getText());}
    ;

In my main function I do then basically this:

  public static void main(String[] args)
  {
     ...
     // Parse the input expression
     parser.stmts();
     CommonAST t = (CommonAST)parser.getAST();
     // Print the resulting tree out in LISP notation
     System.out.println(t.toStringTree());
     CalcTreeWalker walker = new CalcTreeWalker();
     // Traverse the tree created by the parser
     float sum = walker.stmts(t);
     System.out.println("*sum => " + sum);
     ...
   }

When I run my parser on input "5+4 ; 3*2;" I do get this
output (line numbering by me):

001  /opt/jdk32/142_03/bin/java antlr.Tool calc.g
002  ANTLR Parser Generator   Version 2.7.4   1989-2004 jGuru.com
003  ( + 5 4 )
004  <AST>:0:0: expecting EXPR, found '+'
005  *sum => 0.0

The error message in 004 is what I (more or less) expected as
there is no 'EXPR' node. But how would I construct it?

Please be aware that I deliberatly do not want to "summarize"
in the 'expr' rule of my parser tree. 

I wonder whether someone can give me some help?











 
Yahoo! Groups Links

<*> To visit your group on the web, go to:
    http://groups.yahoo.com/group/antlr-interest/

<*> To unsubscribe from this group, send an email to:
    antlr-interest-unsubscribe at yahoogroups.com

<*> Your use of Yahoo! Groups is subject to:
    http://docs.yahoo.com/info/terms/