On Fri, 2008-11-28 at 23:27 +0000, Roly Perera wrote:

Hi,

I've spent some time writing a parser using the Parsec library and was looking forward to being able to plug in some side-behaviour once I'd got the parser working.

Now it seems I can't actually do that in a nice way because Parsec appears to be "fixed" to a simple State monad.

I found this mentioned in the Cafe archives, but not much discussion. Is there a reason Parsec wasn't implemented using the monad transformer approach? Are there any plans to open it up? It's a nice powerful library and a natural thing to want to do for example would be to plug in something like a Reader to track a variable context. I guess one could abuse the State monad to achieve the goal but that feels like the wrong tool for the job.

Any insights appreciated.

Parsec3 is implemented as a monad transformer.