Throwing Exception from from ANTLR4 visitor

[Aravind Kumar]

I am an ANTLR newbie. Here is a grammar for which I am trying to write a Visitor class.

grammar extremelysimpleexpr ;

stat : expr ;
expr : sub ;
sub : add ( '-' add )* ;
add : VAL ( '+' VAL )* 
    | VAL
    ;  


VAL : [0-9]+ ;
[ \t\n\r]+ -> skip ;

Vistor.java

 .........
  public Integer vistAdd(ctx) {
       if (some cond) {
          throw new Exception()
       }
  }
 ..........

The problem is I am not able to throw exception since the generated code does not handle exceptions, the method signature does not have throws exception in its signature. Is there any way out of it ?

stack overflow link for this question

[Terence Parr]

throw a RuntimeException

T

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[Jim Idle]

As Ter says, you can throw an unchecked exception, but actually I question why you want to throw an exception. Exceptions are really for code problems, not for say parsing errors. For errors such as parsing or semantic errors or input problems etc, do not throw exceptions - write a simple error handler class(es) to accumulate problem reports, then print them out at the end of the pass.

Jim

--

[Sam Harwell]

Jim is exactly right here.

 

Note that if for some reason you need to be able to cancel the parsing operation, the runtime includes a standard exception for this purpose:

http://www.antlr.org/api/Java/org/antlr/v4/runtime/misc/ParseCancellationException.html

 

Sam