如何将简单的语法转换为可在PEG.js中使用的语法(预期为"a"但找到"a")

问题描述

我刚开始玩PEG.js，语法有问题(调试时大大简化了):

I've just started playing with PEG.js and have a problem with a grammar (vastly simplified for debugging):

start
  = presingle single
  / preplural plural

presingle
  = "a"
  / "b"

preplural
  = "b"
  / "c"

single
  = "d"
  / "e"

plural
  = "dd"
  / "ee"

我正在使用 https://pegjs.org/online

此语法无法解析bdd.

Line 1, column 3: Expected "a" but "d" found.

这是PEG不能做的事情吗，还是可以将我的语法转换成可以对此进行解析的事情?

Is this something which PEGs cannot do, or can I transform my grammar into something which will parse this?

P.S.如果我尝试解析(错误建议?)bda，我会得到无意义的错误:

P.S. If I try to parse the (erroneously advised?) bda I get the nonsensical error:

Line 1, column 3: Expected "a" but "a" found.

推荐答案

此语法仅更改开始中子句的顺序，并适用于bdd

This grammar changes only the order of the clauses in start and works for bdd

start =
   preplural plural /
    presingle single

presingle
  = "a"
  / "b"

preplural
  = "b"
  / "c"

single
  = "d"
  / "e"

plural
  = "dd"
  / "ee"

并且对于bda显示错误第1行，第3列:预期为"dd"或"ee"，但找到了"a".

and for bda shows error Line 1, column 3: Expected "dd" or "ee" but "a" found.

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