[Haskell-cafe] Re: Improving MTL instances (was: Overlapping/Incoherent instances)

Iavor Diatchki iavor.diatchki at gmail.com
Mon Oct 13 18:12:09 EDT 2008

The currently released version of monadLib does not use overlapping
instances, indeed.
However, in the monadLib  repo (http://github.com/yav/monadlib) there
is a file called "MonadLib4.hs" which contains a version of the
library that is implemented with overlapping instances, so you can
play around with it.  I'd be interested to get feedback on this
version of moandLib.

On Mon, Oct 13, 2008 at 12:44 AM, J. Garrett Morris
<jgmorris at cecs.pdx.edu> wrote:
> On Mon, Oct 13, 2008 at 12:29 AM, Ryan Ingram <ryani.spam at gmail.com> wrote:
>> Of course, the point of this message isn't just to complain.  The
>> overlap implementation was abhorrent and it *is* better now than it
>> was before.
> I'm curious what you find abhorrent about the overlap implementation
> that was there before - in particular, it seems like it was designed
> to handle both the combinatorial explosion and the corner cases you
> mentioned.  Did you find writing the MonadTrans instances unpleasant?
> Was it the presence of overlapping instances at all?
> On Mon, Oct 13, 2008 at 12:35 AM, Don Stewart <dons at galois.com> wrote:
>> I just want to make one small point here encouraging people to try out
>> new 'mtl' libraries. There are lots of *new* monad libraries,
> Without knowing better myself: do any of these libraries address the
> issue Ryan's brought up?  I know that monadLib takes the same approach
> the MTL does to this, and so is likely to have the same difficulties.
>  /g
> --
> I am in here
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