Re: [Haskell-cafe] Alternative versus Monoid

Sorry, I meant Sum and Product for the monoid equivalents of a Num instance. 2011/12/16 Yves Parès

"1) What about the First type? Do we {-# DEPRECATE #-} it?"

Personnaly, I'm in favor of following the same logic than Int: Int itself is *not *a monoid. You have to be specific: it's either Sum or Mult.

It should be the same for Maybe: we remove its instance of Monoid, and we only use First and Last.

2011/12/16 Bas van Dijk

...

On 16 December 2011 05:26, Brent Yorgey wrote:

...

I, for one, would be quite in favor of changing the current Monoid (Maybe a) instance to correspond to the failure-and-prioritized-choice semantics

So lets do this. Some questions:

1) What about the First type? Do we {-# DEPRECATE #-} it?

2) What about the Last type? It could be deprecated in favor of Dual.

3) Do we need a new type (like the current Maybe) for lifting semigroups into a Monoid? IMHO we don't since the semigroup package does a better job with the Option type (like Brent mentioned).

4) How much code will break from this change?

5) Anyone up for proposing this to libraries@haskell.org?

Regards,

Bas

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe