parsing - 如何使用 fparsec 解析由双空格分隔的单词序列？

Question

鉴于输入:

alpha beta gamma  one two three

我怎么能把它解析成下面的？

[["alpha"; "beta"; "gamma"]; ["one"; "two"; "three"]]

当有更好的分隔符(例如__)时，我可以写这个，然后

sepBy (sepBy word (pchar ' ')) (pstring "__")

工作，但在双空间的情况下，第一个 sepBy 中的 pchar 消耗第一个空间，然后解析器失败。

Answer 1

FParsec 手册 says在 sepBy p sep , 如果 sep成功和后续 p失败(不改变状态)，整个sepBy也失败了因此，您的目标是:

制作分隔符 失败 如果遇到多个空格字符；

至 回溯使“内在”sepBy循环愉快地关闭并将控制权传递给“外部”sepBy环形。

以下是两者的方法:

// this is your word parser; it can be different of course,
// I just made it as simple as possible;
let pWord = many1Satisfy isAsciiLetter

// this is the Inner separator to separate individual words
let pSepInner =
    pchar ' '
    .>> notFollowedBy (pchar ' ') // guard rule to prevent 2nd space
    |> attempt                    // a wrapper that would fail NON-fatally

// this is the Outer separator
let pSepOuter =
    pchar ' '
    |> many1  // loop

// this is the parser that would return String list list
let pMain =
    pWord
    |> sepBy <| pSepInner         // the Inner loop
    |> sepBy <| pSepOuter         // the Outer loop

用:

run pMain "alpha beta gamma  one two three"
Success: [["alpha"; "beta"; "gamma"]; ["one"; "two"; "three"]]