code: def p_function_declaration(self, p):
          
          if len(p) == 8:
              p[0] = ast.FuncDecl(
                  identifier=p[2], parameters=None, elements=p[6])
          else:
              p[0] = ast.FuncDecl(
                  identifier=p[2], parameters=p[4], elements=p[7])
docs: function_declaration \
              : FUNCTION identifier LPAREN RPAREN LBRACE function_body RBRACE
              | FUNCTION identifier LPAREN formal_parameter_list RPAREN LBRACE \
                   function_body RBRACE