iteratee alternatives to MonadCatchIO

Gregory Collins greg at
Thu Feb 10 13:51:00 GMT 2011

This is something I've worried about a little bit also. I have a fuzzy
feeling like we're ok since we switched to using "enumerator" and
added a "catch" function for our early termination logic, but I'm not
100% satisfied I understand all of the issues and/or that my analysis
is correct. For now until someone demonstrates otherwise, I think
we're ok with MonadCatchIO, but...


On Thu, Feb 10, 2011 at 3:03 AM, John Lato <jwlato at> wrote:
> Hello,
> Recently many projects have been switching from MonadCatchIO, because that
> library often doesn't do what users want in short-circuiting monads such as
> Error.  I would like to know if there are any comments regarding iteratee
> switching to either monad-peel[0] or monad-control[1].  Currently it looks
> like monad-control is likely to supercede monad-peel in the near future as
> it is more performant, however it's very new and not as well understood.
> As I see it:
> Pro monad-control:
> 1.  exception handling Does The Right Thing[2] with short-circuiting monads
> 2.  faster?
> Contra:
> 1.  Library is less stable, and less well understood
> 2.  Client code may need to be re-written
> Thoughts?
> John
> [0]
> [1]
> [2] I've always expected the behavior provided by MonadCatchIO, and some
> client code may rely upon it, so I'm not convinced it's a universal good.
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Gregory Collins <greg at>

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