[antlr-interest] problem with expression evaluation using AST

[ankit.mehrotra at tcs.com]

Hi,

I have resolved the problem. 

Sorry for the inconvienence

Thanks
Ankit 



ankit.mehrotra at tcs.com 
Sent by: antlr-interest-bounces at antlr.org
12/04/2007 11:36 AM

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Subject
[antlr-interest] problem with expression evaluation using AST







Hi, 

while evaluating expressions in AST's ,  tried a very simple example , 


tree grammar Eval; 
options{ 
tokenVocab = ASTExpr; 
ASTLabelType= CommonTree; 
} 

@header{ 
import java.util.HashMap; 
} 

@members{ 
HashMap memory = new HashMap(); 
} 

prog        :        stat+; 

stat        :        expr {System.out.println($expr.value);} 
        |        ^('=' ID expr) 
                {memory.put($ID.text,new Integer($expr.value));} 
        ; 

expr returns [int value] 
        :        ^('+' a=expr b=expr) {$value = a+b;} 
        |        ^('-' a=expr b=expr) {$value = a-b;} 
        |        ^('*' a=expr b=expr) {$value = a*b;} 
        |        ID 
                { 
                Integer v = (Integer)memory.get($ID.text); 
                if (v != null) $value=v.intValue(); 
                else System.err.println("Undefined Variable "+$ID.text); 
                } 
        |        INT         {$value=Integer.parseInt($INT.text);} 
        ; 

ID        :        ('a'..'z'|'A'..'Z')+; 
INT        :        '0'..'9'+; 

and when have compiled it for generating code, it is giving me this error 

java org.antlr.Tool Eval.g 
ANTLR Parser Generator  Version 3.0.1 (August 13, 2007)  1989-2007 
error(10):  internal error: Eval.g : java.lang.NullPointerException 
org.antlr.tool.GrammarSanity.traceStatesLookingForLeftRecursion(GrammarSanity.ja 

va:105) 
org.antlr.tool.GrammarSanity.checkAllRulesForLeftRecursion(GrammarSanity.java:37 

) 
org.antlr.tool.Grammar.checkAllRulesForLeftRecursion(Grammar.java:1388) 
org.antlr.codegen.CodeGenerator.genRecognizer(CodeGenerator.java:268) 
org.antlr.Tool.processGrammar(Tool.java:347) 
org.antlr.Tool.process(Tool.java:268) 
org.antlr.Tool.main(Tool.java:70) 


Please Help 

Ankit 
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