Fw: [Haskell-cafe] IO within parser
gregorypropf at yahoo.com
Sun Aug 12 01:32:04 EDT 2007
Well the docs ( http://legacy.cs.uu.nl/daan/download/parsec/parsec.html ) hint that setInput and getInput are good for this. I can certainly how they *would* be - if I knew how to pull in files within the parse. Actually I use those functions to do multiple recursive passes but of course you already have the output from the first pass in the parser there. runParser only *looks* like it takes input from a file. Actually it just parses the string you give it and uses the filename arg for error messages only. You still need a way to pull the data into the string from the file.
(Note: I accidentally sent this to Andrew instead of the list originally)
----- Original Message ----
From: Andrew Coppin <andrewcoppin at btinternet.com>
To: haskell-cafe at haskell.org
Sent: Saturday, August 11, 2007 1:25:16 PM
Subject: Re: [Haskell-cafe] IO within parser
Gregory Propf wrote:
> I've been struggling with writing a parser that needs to parse include
> files within source files. So far I cannot get this to work (in
> reality to get work done I wrote a kludge that returns a list of
> include filenames to be run later in a pure IO function. I realized
> that this just amounted to creating my own half-assed monad system so
> I really don't want to use this approach). I have read the tutorials
> I could find on monad transformers but I still don't see what's going
> on. I'm using the Parsec parser library. Here's an
simple example of
> what I've tried. I also tried using liftIO and got a message about
> needing to add an instance of MonadIO. This made more sense but the
> type of liftIO is baffling
The fun part is that Parsec already has a feature for include files...
(I can't remember where the heck it is or how you use it though.)
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