f# – 使用FParsec解析int或float

let parseFloatOrInt lines =
    let rec loop intvalues floatvalues lines =
        match lines with
        | [] -> floatvalues,intvalues
        | line::rest ->
            match run floatWs line with
            | success (r,_,_) -> loop intvalues (r::floatvalues) rest
            | Failure _ -> 
                match run intWs line with
                | success (r,_) -> loop (r::intvalues) floatvalues rest
                | Failure _ -> loop intvalues floatvalues rest

    loop [] [] lines

您正在考虑定义域数据并分离解析器的定义及其在源数据上的使用.这似乎是一种很好的方法,因为随着您的现实项目的进一步发展,您可能需要更多的数据类型.

这是我写它的方式：

/// The resulTing type,or DSL
type MyData =
    | IntValue of int
    | FloatValue of float
    | Error  // special case for all parse @R_750_4895@

// Then,let's define individual parsers:
let pMyInt =
    pint32
    |>> IntValue

// this is an alternative version of float parser.
// it ensures that the value has non-zero fractional part.
// caveat: the naive approach would treat values like 42.0 as Integer
let pMyFloat =
    pfloat
    >>= (fun x -> if x % 1 = 0 then fail "Not a float" else preturn (FloatValue X))
let pError =
    // this parser must consume some input,// otherwise combined with `many` it would hang in a dead loop
    skipAnyChar
    >>. preturn Error

 // Now,the combined parser:
let pCombined =
    [ pMyFloat; pMyInt; pError ]    // note,future parsers will be added here;
                                    // mind the order as float supersedes thE int,// and Error must be the last
    |> List.map (fun p -> p .>> ws) // I'm too lazy to add whitespase skipping
                                    // into each individual parser
    |> List.map attempt             // each parser is optional
    |> choice                       // on each iteration,one of the parsers must succeed
    |> many                         // a loop

注意,上面的代码能够处理任何来源：字符串,流或其他任何来源.您的真实应用可能需要使用文件,但只使用字符串列表可以简化单元测试.

// Now,applying the parser somewhere in the code:
let maybeParseResult =
    match run pCombined myStringData with
    | success(result,_) -> Some result
    | Failure(_,_)      -> None // or anything that inDicates general parse failure

UPD.我根据评论编辑了代码.更新了pMyFloat以确保解析的值具有非零小数部分.