title: antlr visitor is returning an empty parse tree
body: <p>so I'm trying to print the lexemes that are being visited during lexical analysis phase, here's the code of the method that is doing so:</p>
  
  <pre><code>public void parse(String inputFile) {
      InputStream is = System.in;
      if (inputFile != null)
          try {
              is = new FileInputStream(inputFile);
              ANTLRInputStream input = new ANTLRInputStream(is);
              PARVALexer lexer = new PARVALexer(input);
              CommonTokenStream tokens = new CommonTokenStream(lexer);
              PARVAParser parser = new PARVAParser(tokens);
  
              ParseTree tree = parser.prog(); // parse
  
  
              PARVAnalyzer visitor = new PARVAnalyzer();
  
              visitor.visit(tree);
          } catch (Exception e) {
  
              e.printStackTrace();
          }
  
  }
  </code></pre>
  
  <p>if I print <b>tokens</b> , I get a correct output of all the recognized lexemes in the input file, but if I print <b>tree</b> , the output is simply <b>[ ]</b>, and so the method <b>visit(tree)</b> isn't doing anything...
  what could I be doing wrong?</p>