F#, FParsec, and Calling a Stream Parser Recursively

Question

I\'m developing a multi-part MIME parser using F# and FParsec. I\'m developing iteratively, and so this is highly unrefined, brittle code--it only solves my first immediate prob

Answer 1

This is a fragment that might get you going in the right direction.

Get your parsers to spit out something with the same base type. I prefer to use F#'s discriminated unions for this purpose. If you really do need to push values into a Post type, then walk the returned AST tree. That's just the way I'd approach it.

#if INTERACTIVE
#r"""..\..\FParsecCS.dll"""    // ... edit path as appropriate to bin/debug, etc.
#r"""..\..\FParsec.dll"""
#endif

let packet = @"content-type: Multipart/related; boundary=""RN-Http-Body-Boundary""; type=""multipart/related""

--RN-Http-Body-Boundary
Message-ID: <25845033.1160080657073.JavaMail.webmethods@exshaw>
Mime-Version: 1.0
Content-Type: multipart/related; type=""application/xml"";
  boundary=""----=_Part_235_11184805.1160080657052""

------=_Part_235_11184805.1160080657052
Content-Type: Application/XML
Content-Transfer-Encoding: binary
Content-Location: RN-Preamble
Content-ID: <1430586.1160080657050.JavaMail.webmethods@exshaw>"

//XML document begins here...

type AST =
| Document of AST list
| Header of AST list
/// ie. Content-Type is the tag, and it consists of a list of key value pairs
| Tag of string * AST list  
| KeyValue of string * string
| Body of string

The AST DU above could represent a first pass of the example data you posted in your other question. It could be finer grained than that, but simpler is normally better. I mean, the ultimate destination in your example is a Post type, and you could achieve that with some simple pattern matching.