[antlr-interest] Error Handling in AntLR 3 (beginner)

[Rafael C.P.]

Hi! I'm new to AntLR (and, to some extent, to Java as well) and I'd like to
know how to handle errors in AntLR 3. Just an example I'm using to test it:
program
    scope {
        Scope globalScope;
        Scope currentScope;
    }
    @init {
        $program::globalScope = new Scope();
        $program::currentScope = $program::globalScope;
        System.out.println("program start");
        throw new Exception("bla");
    }
    :    declf*
    ;

But I can't throw any exception here, because there isn't a "throws" header
in the method. The actual piece of code requiring it:
declf
    scope {
        FunctionSymbol currentFunction;
    }
    :    ftype IDF {
            if ($program::currentScope.lookup($IDF.text) == null) {
                $declf::currentFunction =
(FunctionSymbol)$program::currentScope.defineFunction($IDF.text,
$ftype.text);
            }
else throw new Exception("Duplicated Entry");


        } args end_declf
    ;

Thanks in advance!

=========
Rafael C.P.
=========
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