javascript - 如何在 PEG.js 中制作可选词

Question

我正在尝试使用 PEG.js 构建一个简单的解析器。我希望用户能够输入一系列关键字，它们之间有一个可选的“AND”，但我似乎无法获得可选和工作。它总是期待它，即使我已经用 ? （零或一）。

将此语法粘贴到http://pegjs.majda.cz/online：

parse = pair+

pair = p:word and? { return p }

word = w:char+ { return w.join(""); }

char = c:[^ \r\n\t] { return c; }

and = ws* 'and'i ws*

ws = [ \t]

我的目标是将这些输入中的任何一个解析为 ["foo", "bar"] 的数组：

foo bar
foo and bar

Answer 1

好的不要紧。我想到了。这是因为我将“and”前面的可选空格作为and规则的一部分，所以它期望规则的其余部分。我只需要将它移出，进入配对规则，如下所示：

parse = pair+
pair  = p:word ws* and? { return p }
word  = w:char+ { return w.join(""); }
char  = c:[^ \r\n\t] { return c; }
and   = 'and'i ws*
ws    = [ \t]

Answer 2

I know this is a very old question, but seeing how it wasn't answered and someone might stumble upon it I'd like to submit my answer:

Program
    = w1:$Word _ wds:(_ "and"? _ w:$Word { return w; })* _  {
        wds.unshift(w1);
        return wds;
    }
Word 
    = [a-zA-Z]+
 _
    = [ ,\t]*

The "and" is optional and you can add as many words as you want. The parser will skip the "and"'s and return a list of the words. I took the liberty of removing commas.

You can try it out https://pegjs.org/online with a string like:

carlos, peter, vincent, thomas, and shirly

Hope it helps someone.

Answer 3

这是我的答案：

start
  = words

words
  = head:word tail:(and (word))* {
    var words = [head];
    tail.forEach(function (word) {
      word = word[1];
      words.push(word);
    })
    return words;
  }

and
  = ' and '
  / $' '+

word
  = $chars

chars 'chars'
  = [a-zA-Z0-9]+