docs: def parse(self):
          """
          Tokenizes and parses an arithmetic expression into a parse tree.
  
          @return: Returns a token string.
          @rtype: lems.parser.expr.ExprNode
          """
          #print("Parsing: %s"%self.parse_string)
          self.tokenize()
          if self.debug: print("Tokens found: %s"%self.token_list)
          
          try:
              parse_tree = self.parse2()
          except Exception as e:
                  raise e
          return parse_tree