[Haskell-cafe] Restricted file reading monad

[Henning Thielemann]

On Thu, 2 Oct 2008, George Pollard wrote:

> Hello all,
>
> I'm currently working on a (toy) ID3 [1] tag reader, which made me think
> of a library which might be quite useful.
>
> The structure of an ID3 tag goes something like this:
>
> Header:
> - total size of tag
> - other header info
> A series of frames, each with:
> - total size of frame
> - other header info
> - frame data
>
> Since the ID3 tag as a whole has size information, I need to pass that
> into the frame-reading functions to ensure that I never read past the
> end of the total header. This exact same requirement is present within
> the frame-reading function itself; it must read the frame data without
> reading past the end of the frame.

I've done exactly this for a MIDI file parser. It uses a State monad 
transformer which handles the number of remaining bytes in the chunk.
    http://darcs.haskell.org/midi/src/Sound/MIDI/Parser/Restricted.hs