Update Semigroup, Semiring and Monoid docs

[aballano]

Make Semigroup's maybeCombine to use nullables instead of Option

From #2313 to the right branch 😅 cc @rachelcarmena

[aballano]

Not sure exactly what's the problem:

error: unresolved reference: list
import arrow.core.list
                  ^
error: unresolved reference: list
Semigroup.list<Int>().run {

It works for numbers tho, and list is available in master, any thoughts?

[nomisRev]

👌

[rachelcarmena]

Not sure exactly what's the problem:

error: unresolved reference: list
import arrow.core.list
                  ^
error: unresolved reference: list
Semigroup.list<Int>().run {

It works for numbers tho, and list is available in master, any thoughts?

@aballano , some clues 🙌

Look at the content of the arrow-core-data.jar file:

arrow/core/ListMonoid.class
...
arrow/core/IntSemigroup.class
arrow/core/IntMonoid.class
...
arrow/core/OptionSemigroup.class
arrow/core/OptionMonoid.class

There isn't arrow/core/ListSemigroup.class (just arrow/core/NonEmptyListSemigroup.class).

Maybe the reason is the implementation of list for Semigroup:

fun <A> Semigroup.Companion.list(): Semigroup<List<A>> =
  Monoid.list()

fun <A> Monoid.Companion.list(): Monoid<List<A>> =
  ListMonoid as Monoid<List<A>>

It calls list for Monoid.

However, the implementation for Int and Option is different:

• Int
• Option

[danimontoya]

It was only missing removing some of the imports that are not needed anymore.. because some extensions are now part of the companion object itself.. this should fix it:
#2339

[danimontoya]

🙌

[rachelcarmena]

👏