transformers: remove instance MonadFix ExceptT and ErrorT

[Henning Thielemann]

Am 12.08.2014 um 21:17 schrieb Edward Kmett:

> so it seems the logical extension of your request would be to strip all
> such instances,

one by one, please :-)


Can someone provide me examples of useful applications of mfix on Maybe, 
ExceptT etc.?

I mean, all those mfix instances contain an "error" - wouldn't it be 
better if the user would do such dirty things and insert a more specific 
error message?

Admittedly, I have used mfix only once so far, at all, namely on an RWS 
monad, as far as I remember. Eventually I chose another design, because 
the mfix way was too fragile.