On 22/12/10 19:17, John Smith wrote:
On 22/12/2010 19:03, Simon Marlow wrote:
On 14/12/2010 08:35, Isaac Dupree wrote:
On 12/14/10 03:13, John Smith wrote:
I would like to formally propose that Monad become a subclass of
Applicative, with a call for consensus by 1 February. The change is
described on the wiki at
http://haskell.org/haskellwiki/Functor-Applicative-Monad_Proposal,
That page isn't written as a proposal yet, it's written as a bunch of
ideas. I would be happy to see something along the lines of Bas van
Dijk's work
http://permalink.gmane.org/gmane.comp.lang.haskell.libraries/14740 .
This is a proposal with far-reaching consequences, and with several
alternative designs. I'm not sure I understand all
the tradeoffs. Some parts of the proposal are orthogonal to the rest
(e.g. changing fmap to map), and should probably be
considered separately.
Could someone please write a detailed proposal, enumerating all the
pros and cons, and the rationale for this design
compared to other designs?
Cheers,
Simon
The wiki page was admittedly too broad of scope when I first wrote it,
and it's getting broader with time.
The ticket at http://hackage.haskell.org/trac/ghc/ticket/4834 has
patches for only one change, making Monad a subclass of Applicative. (I
would update the description to make this clear, but I can't edit the
ticket description, so this has been relegated to a comment.)
Dealing with one issue at a time is great. But even with this single
change, we need to weight up the advantages and disadvantages - it's
difficult to make an assessment without trawling through long email
threads, and yet I don't want to let the proposal pass without comment.
So it would help a lot if someone could take the time to explain the
design space and the tradeoffs.
I know for example I have lots of code that defines a Monad instance and
doesn't need an Applicative instance, so this change will force me to
jump through hoops that I don't need to.
Cheers,
Simon
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