On Wed, Jul 21, 2010 at 11:05:02AM -0700, Iavor Diatchki wrote:
PS: About (+ e) being used in papers on monads: the instance we are adding is actually "Either e" which would be confusing enough for someone who is just learning about these things. It would be even more confusing when---having finally figured out the correspondence---they tried to define the instance from the paper and got an "overlapping instance" error.
Yes, Either is the Prelude version of +. As for the overlap, the same thing will happen if they read in those papers about (->) r and try to declare that -- it's already there.
PPS: I don't mean to sound too negative here (I am told I have some skill for it though :-). Examples of the utility of this instance would be most welcome though.
Those papers have a few.