code: def makenode(clss, symbol, *nexts):
          
          result = clss(symbol)
          for i in nexts:
              if i is None:
                  continue
              if not isinstance(i, clss):
                  raise NotAnAstError(i)
              result.appendChild(i)
  
          return result
docs: Stores the symbol in an AST instance,
          and left and right to the given ones