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

Hello, 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. -Iavor On Mon, Oct 13, 2008 at 12:44 AM, J. Garrett Morris wrote:

On Mon, Oct 13, 2008 at 12:29 AM, Ryan Ingram 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 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

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