code: def p_if_stmt(p):
      
      if len(p) == 7:
          p[0] = node.if_stmt(cond_expr=p[2], then_stmt=p[4], else_stmt=p[5])
      elif len(p) == 8:
          p[0] = node.if_stmt(cond_expr=p[3], then_stmt=p[5], else_stmt=p[6])
      else:
          assert 0
docs: if_stmt : IF expr sep stmt_list_opt elseif_stmt END_STMT
              | IF LPAREN expr RPAREN stmt_list_opt elseif_stmt END_STMT