add setMonoid

[drostron]

gitter discussion

[codecov-io]

Current coverage is 63.82%

Merging #497 into master will increase coverage by +0.92% as of d74e9fc

@@            master    #497   diff @@
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  Files          154     155     +1
  Stmts         2359    2366     +7
  Branches        66      66       
  Methods          0       0       
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+ Hit           1484    1510    +26
  Partial          0       0       
+ Missed         875     856    -19

Review entire Coverage Diff as of d74e9fc

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[non]

👍 Thanks!

[ceedubs]

It will probably require adding a questionable Eq instance for sets, but could we test this against the monoid laws?

[drostron]

Sure. I need to familiarize with law checking a bit more first (been itching to do so for awhile so this is a welcomed opportunity). The next few days are filled, but should have some time after that.

[drostron]

Pushed a commit adding law checking for setMonoidInstance. @ceedubs, I'm curious if this PR introduces a questionable Eq instance for sets. If so I'm interested to learn more.

[ceedubs]

👍 looks good to me.

I was surprised to see that Eq instance for sets was in scope. It looks like algebra has provided one for quite a while (not introduced with this PR). I suppose it makes sense to have it if you are working with Set, since it's based on universal equality anyway.

[ceedubs]

The only thing added since @non gave a 👍 is law-checking which I can't imagine he would be opposed to :). I'm going to merge this. Thanks!