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如何使用fparsec解析由双空格分隔的单词序列?

fparsec f# parsing

2

Simon P · 技术社区 · 6 年前

给定输入:

alpha beta gamma  one two three

我怎么能把它分解成下面的呢?

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

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

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

2 回复 | 直到 6 年前

1

2

Be Brave Be Like Ukraine 6 年前

says 那在哪 sepBy p sep sep 成功与后续 p sepBy 也失败了。因此,您的目标是:

制造分离器如果遇到多个空格字符;
到所以“内在的” 循环愉快地关闭并将控制权传递给“外部” 塞比 循环。

以下是如何做到这两者:

// 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

用途:

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

2

rmunn 6 年前

我建议更换 sepBy word (pchar ' ') 像这样:

let pOneSpace = pchar ' ' .>> notFollowedBy (pchar ' ')
let pTwoSpaces = pstring "  "
// Or if two spaces are allowed as separators but *not* three spaces...
let pTwoSpaces = pstring "  " .>> notFollowedBy (pchar ' ')
sepBy (sepBy word pOneSpace) pTwoSpaces

注意:没有测试(因为我现在没有时间),只是在答案框中输入。所以测试一下,以防我在什么地方出错。