Hi,

I'm looking for an efficient IO library geared towards support for  
things like lexers. The essential features are:
* Support for easily backing up in the IO stream. That is, it should  
have an API for saving one's place and then later discarding that save  
(i.e. committing to current position) or restoring the IO stream to  
the saved location.
* Support for extracting and/or accessing sections of the stream  
(particularly, those between the last save point and the current  
position).

It looks like the Lexing module has these features baked in, but it  
doesn't seem to expose them to the user.  Does anyone have any other  
suggestions?

Thanks,
Yitzhak
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Yitzhak Mandelbaum