Re: PROPOSAL: Add Map/IntMap newtypes for different Monoid to containers

If you have to choose between the two use Ben's code, reducers is in hospice on life-support, and is unlikely to see anything more than a maintenance release in the foreseeable future. -Edward On Fri, Mar 24, 2017 at 1:34 PM, Ben Gamari wrote:

Merijn Verstraaten writes:

...

I would like to propose adding a newtype wrapper (with all relevant instances) for Map and IntMap (if I missed any other applicable type in containers, let me know).

This newtype should differ in Monoid/Semigroup instance from Map/IntMap by switching:

Ord k => Semigroup (Map k v) Ord k => Monoid (Map k v)

to:

(Ord k, Semigroup v) => Semigroup (Map k v) (Ord k, Monoid v) => Monoid (Map k v) or (Ord k, Semigroup v) => Monoid (Map k v)

Any opinions on the overall idea? Opinions on which Monoid instance? Bikeshed for the newtype names?

For what it's worth, I provide precisely this in my monoidal-containers package [1]. Also, Edward Kmett provides a similar idea in his reducers package [2].

Cheers,

- Ben

[1] https://hackage.haskell.org/package/monoidal-containers [2] https://hackage.haskell.org/package/reducers-3.12.1/docs/ Data-Semigroup-Union.html

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