感谢您对我的第一篇文章和我关于这个项目的第二篇文章的回复。这个问题与第一个问题基本相同，但我的代码根据收到的关于这两个问题的反馈进行了更新。如何递归调用我的解析器？
我在挠头，茫然地盯着代码。我不知道从这里去哪里。那是我转向stackoverflow的时候。
我在代码注释中包含了我收到的编译时错误。一个绊脚石可能是我受歧视的工会。我与受歧视的工会合作的不多，所以我可能会错误地使用我的工会。
我正在使用的示例 POST（我在前两个问题中包含的部分内容）由一个边界组成，该边界包括具有新边界的第二个帖子。第二个帖子包括由第二个边界分隔的几个附加部分。这几个附加部分中的每一个都是由标题和 XML 组成的新帖子。
我在这个项目中的目标是构建一个在我们的 C# 解决方案中使用的库，该库采用流并将 POST 递归地解析为标题和部分。我真的希望 F# 在这里大放异彩。
namespace MultipartMIMEParser
open FParsec
open System.IO
type Header = { name : string
; value : string
; addl : (string * string) list option }
type Content = Content of string
| Post of Post list
and Post = { headers : Header list
; content : Content }
type UserState = { Boundary : string }
with static member Default = { Boundary="" }
module internal P =
let ($) f x = f x
let undefined = failwith "Undefined."
let ascii = System.Text.Encoding.ASCII
let str cs = System.String.Concat (cs:char list)
let makeHeader ((n,v),nvps) = { name=n; value=v; addl=nvps}
let runP p s = match runParserOnStream p UserState.Default "" s ascii with
| Success (r,_,_) -> r
| Failure (e,_,_) -> failwith (sprintf "%A" e)
let blankField = parray 2 newline
let delimited d e =
let pEnd = preturn () .>> e
let part = spaces
>>. (manyTill
$ noneOf d
$ (attempt (preturn () .>> pstring d)
<|> pEnd)) |>> str
in part .>>. part
let delimited3 firstDelimiter secondDelimiter thirdDelimiter endMarker =
delimited firstDelimiter endMarker
.>>. opt (many (delimited secondDelimiter endMarker
>>. delimited thirdDelimiter endMarker))
let isBoundary ((n:string),_) = n.ToLower() = "boundary"
let pHeader =
let includesBoundary (h:Header) = match h.addl with
| Some xs -> xs |> List.exists isBoundary
| None -> false
let setBoundary b = { Boundary=b }
in delimited3 ":" ";" "=" blankField
|>> makeHeader
>>= fun header stream -> if includesBoundary header
then
stream.UserState <- setBoundary (header.addl.Value
|> List.find isBoundary
|> snd)
Reply ()
else Reply ()
let pHeaders = manyTill pHeader $ attempt (preturn () .>> blankField)
let rec pContent (stream:CharStream<UserState>) =
match stream.UserState.Boundary with
| "" -> // Content is text.
let nl = System.Environment.NewLine
let unlines (ss:string list) = System.String.Join (nl,ss)
let line = restOfLine false
let lines = manyTill line $ attempt (preturn () .>> blankField)
in pipe2 pHeaders lines
$ fun h c -> { headers=h
; content=Content $ unlines c }
| _ -> // Content contains boundaries.
let b = "--" + stream.UserState.Boundary
// VS complains about pContent in the following line:
// Type mismatch. Expecting a
// Parser<'a,UserState>
// but given a
// CharStream<UserState> -> Parser<Post,UserState>
// The type 'Reply<'a>' does not match the type 'Parser<Post,UserState>'
let p = pipe2 pHeaders pContent $ fun h c -> { headers=h; content=c }
in skipString b
>>. manyTill p (attempt (preturn () .>> blankField))
// VS complains about Content.Post in the following line:
// Type mismatch. Expecting a
// Post list -> Post
// but given a
// Post list -> Content
// The type 'Post' does not match the type 'Content'
|>> Content.Post
// VS complains about pContent in the following line:
// Type mismatch. Expecting a
// Parser<'a,UserState>
// but given a
// CharStream<UserState> -> Parser<Post,UserState>
// The type 'Reply<'a>' does not match the type 'Parser<Post,UserState>'
let pStream = runP (pipe2 pHeaders pContent $ fun h c -> { headers=h; content=c })
type MParser (s:Stream) =
let r = P.pStream s
let findHeader name =
match r.headers |> List.tryFind (fun h -> h.name.ToLower() = name) with
| Some h -> h.value
| None -> ""
member p.Boundary =
let header = r.headers
|> List.tryFind (fun h -> match h.addl with
| Some xs -> xs |> List.exists P.isBoundary
| None -> false)
in match header with
| Some h -> h.addl.Value |> List.find P.isBoundary |> snd
| None -> ""
member p.ContentID = findHeader "content-id"
member p.ContentLocation = findHeader "content-location"
member p.ContentSubtype = findHeader "type"
member p.ContentTransferEncoding = findHeader "content-transfer-encoding"
member p.ContentType = findHeader "content-type"
member p.Content = r.content
member p.Headers = r.headers
member p.MessageID = findHeader "message-id"
member p.MimeVersion = findHeader "mime-version"
编辑
为了回应我迄今为止收到的反馈（谢谢！），我做了以下调整，收到注释的错误：
let rec pContent (stream:CharStream<UserState>) =
match stream.UserState.Boundary with
| "" -> // Content is text.
let nl = System.Environment.NewLine
let unlines (ss:string list) = System.String.Join (nl,ss)
let line = restOfLine false
let lines = manyTill line $ attempt (preturn () .>> blankField)
in pipe2 pHeaders lines
$ fun h c -> { headers=h
; content=Content $ unlines c }
| _ -> // Content contains boundaries.
let b = "--" + stream.UserState.Boundary
// The following complaint is about `pContent stream`:
// This expression was expected to have type
// Reply<'a>
// but here has type
// Parser<Post,UserState>
let p = pipe2 pHeaders (fun stream -> pContent stream) $ fun h c -> { headers=h; content=c }
in skipString b
>>. manyTill p (attempt (preturn () .>> blankField))
// VS complains about the line above:
// Type mismatch. Expecting a
// Parser<Post,UserState>
// but given a
// Parser<'a list,UserState>
// The type 'Post' does not match the type ''a list'
// See above complaint about `pContent stream`. Same complaint here.
let pStream = runP (pipe2 pHeaders (fun stream -> pContent stream) $ fun h c -> { headers=h; content=c })
我尝试加入Reply ()s，但它们只是返回解析器，意思是c上面变成了 aParser<...>而不是Content. 这似乎是一种倒退，或者至少是在错误的方向上。不过我承认我的无知，欢迎指正！