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CommutativeSemigroup[A] => CommutativeMonoid[Option[A]] #2725

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ceedubs opened this issue Feb 4, 2019 · 4 comments
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CommutativeSemigroup[A] => CommutativeMonoid[Option[A]] #2725

ceedubs opened this issue Feb 4, 2019 · 4 comments

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@ceedubs
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ceedubs commented Feb 4, 2019

It looks like having a CommutativeSemigroup[A] currently doesn't get you CommutativeMonoid[Option[A]]. I think that's something that we should be able to provide. Does anyone have a reason not to include this instance?
@ctongfei
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ctongfei commented Feb 8, 2019

Can we get a Monoid[Option[A]] from a Semigroup[A] in cats now?

@LukaJCB
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LukaJCB commented Feb 8, 2019

@ctongfei It's in fact the standard instance :)
See here: https://github.com/typelevel/cats/blob/master/kernel/src/main/scala/cats/kernel/instances/option.scala#L9

@ctongfei
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ctongfei commented Feb 8, 2019

@LukaJCB Ahh thanks!

@kailuowang
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kailuowang commented Feb 8, 2019 •
edited

to fix this we need to move the current Monoid instance to OptionInstances0, so that we can add the commutative one on top.
This change will be binary breaking on scala 2.11 though. There might be convoluted ways to do it in scala2.11 but it's not obvious to me. If it's not urgent, shall we schedule it to 2.1?

valydia pushed a commit to valydia/cats that referenced this issue May 8, 2019
Add CommutativeMonoid[Option[A]] instance (typelevel#2725)
6697f83
valydia pushed a commit to valydia/cats that referenced this issue May 8, 2019
Add CommutativeMonoid[Option[A]] instance (typelevel#2725)
4ebc19c
valydia pushed a commit to valydia/cats that referenced this issue May 8, 2019
Add CommutativeMonoid[Option[A]] instance (typelevel#2725)
5e555d6
valydia pushed a commit to valydia/cats that referenced this issue May 28, 2019
Add CommutativeMonoid[Option[A]] instance (typelevel#2725)
8791efa
kailuowang pushed a commit that referenced this issue Nov 6, 2019
@valydia @kailuowang
CommutativeMonoid[Option[A]] from CommutativeSemigroup (#2834)
1a6d2c3 
* Add FreeT.inject helper function (#1534)

* Rename FreeT.inject to FreeT.liftInject (#1534)

* Add Free.liftInject helper function (#1534)

* Add CommutativeMonoid[Option[A]] instance (#2725)

* Update laws

* Format the codebase

* Remove unnecessary change

* Make instance helper class private
@kubukoz kubukoz mentioned this issue Dec 21, 2019
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@LukaJCB LukaJCB closed this as completed Dec 21, 2019
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4 participants
@kailuowang @ceedubs @ctongfei @LukaJCB