public final EsperParser.factor_return factor() throws RecognitionException {
        EsperParser.factor_return retval = new EsperParser.factor_return();
        retval.start = input.LT(1);


        Object root_0 = null;

        Token set20=null;

        Object set20_tree=null;

        try {
            // C:\\Users\\Alex\\Dropbox\\EclipseWorkspace\\esper-compiler\\src\\compiler\\Esper.g:38:9: ( DIGITS | IDENTIFIER | NULLITY | INFINITY | NEGATIVEINFINITY )
            // C:\\Users\\Alex\\Dropbox\\EclipseWorkspace\\esper-compiler\\src\\compiler\\Esper.g:
            {
            root_0 = (Object)adaptor.nil();


            set20=(Token)input.LT(1);

            if ( input.LA(1)==DIGITS||input.LA(1)==IDENTIFIER||input.LA(1)==INFINITY||(input.LA(1) >= NEGATIVEINFINITY && input.LA(1) <= NULLITY) ) {
                input.consume();
                adaptor.addChild(root_0, 
                (Object)adaptor.create(set20)
                );
                state.errorRecovery=false;
            }
            else {
                MismatchedSetException mse = new MismatchedSetException(null,input);
                throw mse;
            }


            }

            retval.stop = input.LT(-1);


            retval.tree = (Object)adaptor.rulePostProcessing(root_0);
            adaptor.setTokenBoundaries(retval.tree, retval.start, retval.stop);

        }
        catch (RecognitionException re) {
            reportError(re);
            recover(input,re);
    	retval.tree = (Object)adaptor.errorNode(input, retval.start, input.LT(-1), re);

        }

        finally {
        	// do for sure before leaving
        }
        return retval;
    }