CODEWITHSUNDEEP
antlr
Preeti
Preeti

Reputation: 93

Error handeling in antlr 3.0

I need to Report customized error when ever user input does not match our defined rules.

Here is my code:

grammar second1;

@lexer::members {
@Override
public void reportError(RecognitionException e) {
    System.out.println("Throwing Exception: "+ e.getMessage());
    throw new IllegalArgumentException(e);
 }
}

@parser::members {
private boolean inbounds(Token t, int min, int max, String methodName) {
   int n = Integer.parseInt(t.getText());    
   if(n >= min && n <= max) {
     return true;
   }
   else {
     System.out.println("The range for value accepted by " + methodName+" is "+min +"-" + max );
     return false;
   }
 }
}

expr       :  SET attribute EOF;

attribute  :  Value1 int1:integer1["Value1"] { System.out.println("Accepted"); }
       |  Value2 integer2 ["Value2"] { System.out.println("Accepted"); }
       ;
exception[int1]: 
        catch[Exception e] {System.out.println("Error Reported for int1");}
exception: 
        catch[Exception e] {System.out.println("General error Reported");}

integer1 [String methodName]   :  Int { inbounds($Int,0,1000,methodName) }? ;
integer2 [String methodName]  :  Int { inbounds($Int,0,10000,methodName) }? ;
Int        :  '0'..'9'+;

SET        :  'set';
Value1     :  'value';
Value2     :  'value2'; 

fragment WS
  : (' ' | '\t')
 ;

But while compiling this code I am getting the following errors:

error(100): second1.g:26:22: syntax error: antlr: second1.g:26:22: unexpected token: int1  
error(100): second1.g:29:17: syntax error: antlr: second1.g:29:17: unexpected token: :  
error(100): second1.g:32:10: syntax error: antlr: second1.g:32:10: unexpected token: catch  
error(100): second1.g:0:0: syntax error: assign.types: <AST>:0:0: unexpected AST node: <end-of-block>  
error(100): second1.g:0:0: syntax error: assign.types: <AST>:0:0: unexpected end of subtree  
error(100): second1.g:0:0: syntax error: define: <AST>:0:0: unexpected AST node: <end-of-block>  
error(100): second1.g:0:0: syntax error: define: <AST>:0:0: unexpected AST node: <end-of-block>  
error(100): second1.g:0:0: syntax error: define: <AST>:0:0: unexpected end of subtree  
error(106): second1.g:26:27: reference to undefined rule: integer1  
error(106): second1.g:27:22: reference to undefined rule: integer2  
warning(105): second1.g:27:15: no lexer rule corresponding to token: Value2  
warning(105): second1.g:26:15: no lexer rule corresponding to token: Value1  
warning(105): second1.g:24:15: no lexer rule corresponding to token: SET

What should I do? :(
I checked on net, this is how we handle exception in ANTLR 3.x
Why is it not working in my case then :(
Please help me out.

Upvotes: 1

Views: 2034

Answers (1)

ilyaigpetrov
ilyaigpetrov

Reputation: 3883

"Catch blocks are no longer prefixed with 'exception' keyword", so your attribute rule would be:

attribute  :
      Value1 integer1["Value1"] { System.out.println("Accepted"); }
   |  Value2 integer2["Value2"] { System.out.println("Accepted"); }
   ;
catch[Exception e] {System.out.println("General error Reported");}

Next, you have overriden lexer's reportError method, not the one of the parser (where inbound check is invoked).

To make the parser throw error instead of recovery you can copy reportError to @parser::members section and then you can get "General error Reported".

But if you want not to stop antlr's recovery mechanism, but to make error messages more informative, you can read this free excerpt from The Definitive ANTLR Reference and define getErrorMessage method:

public String getErrorMessage(RecognitionException e, String[] tokenNames)
{
    List stack = getRuleInvocationStack(e, this.getClass().getName());
    String msg = null;
    if ( e instanceof NoViableAltException ) {
       NoViableAltException nvae = (NoViableAltException)e;
       msg = " no viable alt; token="+e.token+
          " (decision="+nvae.decisionNumber+
          " state "+nvae.stateNumber+")"+
          " decision=<<"+nvae.grammarDecisionDescription+">>";
    }
    else if(  e instanceof FailedPredicateException  ) {
       FailedPredicateException fpe = (FailedPredicateException)e;
       msg = "failed predicate; token="+fpe.token+
              " (rule="+fpe.ruleName+" predicate="+fpe.predicateText+")";
    }
    else {
       msg = super.getErrorMessage(e, tokenNames);
    }
    return stack+" "+msg;
}
public String getTokenErrorDisplay(Token t) {
    return t.toString();
}

Upvotes: 2

Related Questions