[Haskell-cafe] Parsec and network data

[Derek Elkins]

On Fri, 2008-08-29 at 20:01 +0200, Johannes Waldmann wrote:
> Donn Cave wrote:
> 
> > ...  I would implement the network service
> > input data stream myself, with timeouts, encryption, whatever as required,
> > and then apply the parser to available data as a simple, pure function
> > that returns NNTP results and whatever data remains.  So the parser would
> > never see any streams or handles or anything, it would just get strings
> > to parse.
> 
> A likely problem with that is that your implementation  of the "input
> data stream" will still need to parse some information from it.
> So you're going to replicate code from the parser.
> 
> I think the following is analoguous.
> 
> Imagine you're writing a parser for a simple programming language.
> A program is a sequence of statements.
> Fine, you do "readFile" (once) and then apply a pure Parsec parser.
> 
> Then you decide to include "import" statements in your  language.
> Suddenly the parser needs to do IO. Assume the import statements
> need not be the first statements  of the program
> (there may be headers, comments etc. before).
> Then you really have to interweave the parsing and the IO.
> 
> If anyone has a nice solution to this, please tell. - J.W.

Using parsec3 you can just do exactly what you said.