Menhir的部分解析和恢复

Question

有一个很小calculator in Sedlex and Menhir。现在，我想让计算器能够解析像 1+ 这样的表达式。所以我将parser.mly修改为

... ...
main:
    expr EOL                {  }
;
expr [@recovery (E_int 0)]:
    INT                     { E_int  }
  | BOOL                    { E_bool  }
... ...

但评估 1+ 仍然返回错误 Fatal error: exception Parser.MenhirBasics.Error。

有人能帮忙吗？

Answer 1

我的评论的补充摘要：

[@recovery ...] 是 Merlin 特有的结构
截至目前（13/02/2022），仍然可以通过使用特殊的 error 标记来定义您自己的错误恢复，如下所示：

main:
    expr EOL                {  }
;
expr [@recovery (E_int 0)]:
    INT                     { E_int  }
  | BOOL                    { E_bool  }
  | error                   { E_int 0 }

来自menhir's manual：

If the error token is used to survive an error and continue parsing, then the legacy strategy should be selected.
--strategy strategy. This switch selects an error-handling strategy, to be used by the code back-end, the table back-end, and the reference interpreter. The available strategies are legacy and simplified.

来自OCaml weekly news：

Grammars that make more complex use of the error token, and therefore need the legacy strategy, cannot be compiled by the new code back-end. As a workaround, it is possible to switch to the table back-end (using --table --strategy legacy) or to the ancient code back-end (using --code-ancient). In the long run, we recommend abandoning the use of the error token. Support for the error token may be removed entirely at some point in the future.

这种做事方式很可能在不久的将来行不通，但现在行得通，而且它似乎是执行 OP 要求的最简单方法。

Menhir的部分解析和恢复

Partial parsing and recovery of Menhir

parsing

ocaml

menhir

merlin