Refactoring Semigroup/Monoid

[Simon Peyton-Jones]

| well, judging from SPJ's last comment I found on that topic, the
| proposal seems to have been stuck, and it seems we have to make our
| desire for that feature more apparent:

Correct.  There are several factors here.  

First, in the last several months I have been overwhelmed with non-GHC stuff so anything non-critical has gone on the back burner. Sorry about that.

Second, and more important, this default-superclass stuff is a pretty complex feature, with a number of non-obvious design choices. Some are articulated on the wiki page
	http://hackage.haskell.org/trac/ghc/wiki/DefaultSuperclassInstances
but I'm not certain that all are.  

Before moving forward with something as big as this, I think we would all want reassurance that 

(a) the need is widely felt, and fixing it important 
    enough to pay for the language complexity that comes with it.
(b) the design is well motivated, and well worked out, including awkward corners; 
(c) there is a consensus about the particular design choices;

All that said, I am still concerned that the design as described on the wiki page is just rather complicated.  Will nothing simpler do?  Perhaps not, but I think that its complexity has been a background inhibiting factor.

Simon

| -----Original Message-----
| From: libraries-bounces at haskell.org [mailto:libraries-
| bounces at haskell.org] On Behalf Of Herbert Valerio Riedel
| Sent: 17 November 2012 15:21
| To: Dan Burton
| Cc: Henning Thielemann; Jake McArthur; Haskell Libraries
| Subject: Re: Refactoring Semigroup/Monoid
| 
| Dan Burton <danburton.email at gmail.com> writes:
| 
| > http://hackage.haskell.org/trac/ghc/wiki/DefaultSuperclassInstances
| >
| > What is the status on this?
| 
| well, judging from SPJ's last comment I found on that topic, the
| proposal seems to have been stuck, and it seems we have to make our
| desire for that feature more apparent:
| 
| ,----
| | From:
| | <http://permalink.gmane.org/gmane.comp.lang.haskell.libraries/16212>
| |
| |  >  With regard to [1], default superclass instances, is there already
| | a plan to  > implement them? And if so, when is it expected to be
| finished?
| |  >
| |  >  [1]
| | http://hackage.haskell.org/trac/ghc/wiki/DefaultSuperclassInstances
| |
| |  It definitely won't be in 7.4 I'm afraid.
| |
| |  One thing that would be motivating would be a list of people who
| | actively want default superclass instances and why you want them.  My
| | own priorities for implementing stuff are much influenced by what
| | GHC's users seem to value.  I've added an "Applications" section to
| | [1]; do add yourself and sketch how you'd use the new feature.
| `----
| 
| 
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