add scaladoc for Comonad / CoFlatMap

[stew]

core/src/main/scala/cats/Comonad.scala
core/src/main/scala/cats/CoFlatMap.scaal

[lukewyman]

@stew I'd like to work on this one (and have started already). Question on the scaladocs: do we want to make these comments nice and pretty complete with examples (like the comments in cats.Arrow)?

If the answer is yes, then it doesn't look like we have instances (or complete combinators on our instances) for Comonad and CoFlatMap. Should I go ahead and polish this up?

And if the answer to that is yes, how on earth does one extract `A

[lukewyman]

And if the answer to that is yes, how on earth does one extract A from None without knowing what `A

[lukewyman]

without knowing what A is?

[adelbertc]

We have a couple instances for Comonad, see Id and Eval. Id is defined as type Id[A] = A so extraction is identity. Eval is a data type that captures evaluation strategy of a value, extracting is equivalent to executing the strategy to compute the value.

re: Scaladoc w/ examples, that would be good. We use sbt-doctest to make sure the examples are compile-able and correct, so you may want to look into that.

[lukewyman]

Do there exist possible implementations for extract on things like 'NoneandList()`, as in is that solvable?

[adelbertc]

Nope, for the reason you stated previously
On Feb 16, 2016 17:45, "Luke Wyman" notifications@github.com wrote:

Do there exist possible implementations for extract on things like 'None
andList()`, as in is that solvable?

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#131 (comment).

[ceedubs]

NonEmptyList is probably a good item for a Comonad example. Other than the fact that it will show up as OneAnd in the toString representation, which could be a bit confusing...

[kailuowang]

fixed by #898