Merge pull request #898 from lukewyman/topic/scaladoc-coflat-comonad

Topic/scaladoc coflat comonad #131

core/src/main/scala/cats/CoflatMap.scala

@@ -3,11 +3,47 @@ package cats
 import simulacrum.typeclass
 
 /**
- * Must obey the laws defined in cats.laws.CoflatMapLaws.
- */
+  * `CoflatMap` is the dual of `FlatMap`.
+  *
+  * Must obey the laws in cats.laws.CoflatMapLaws
+  */
 @typeclass trait CoflatMap[F[_]] extends Functor[F] {
+
+  /**
+    * `coflatMap` is the dual of `flatMap` on `FlatMap`. It applies
+    * a value in a Monadic context to a function that takes a value
+    * in a context and returns a normal value.
+    *
+    * Example:
+    * {{{
+    * scala> import cats.std.option._
+    * scala> import cats.Monad
+    * scala> import cats.CoflatMap
+    * scala> val fa = Monad[Option].pure(3)
+    * scala> def f(a: Option[Int]): Int = a match {
+    *      | case Some(x) => 2 * x
+    *      | case None => 0 }
+    * scala> CoflatMap[Option].coflatMap(fa)(f)
+    * res0: Option[Int] = Some(6)
+    * }}}
+    */
   def coflatMap[A, B](fa: F[A])(f: F[A] => B): F[B]
 
+  /**
+    * `coflatten` is the dual of `flatten` on `FlatMap`. Whereas flatten removes
+    * a layer of `F`, coflatten adds a layer of `F`
+    *
+    * Example:
+    * {{{
+    * scala> import cats.std.option._
+    * scala> import cats.Monad
+    * scala> import cats.CoflatMap
+    * scala> val fa = Monad[Option].pure(3)
+    * fa: Option[Int] = Some(3)
+    * scala> CoflatMap[Option].coflatten(fa)
+    * res0: Option[Option[Int]] = Some(Some(3))
+    * }}}
+    */
   def coflatten[A](fa: F[A]): F[F[A]] =
     coflatMap(fa)(fa => fa)
 }

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

@@ -2,9 +2,29 @@ package cats
 
 import simulacrum.typeclass
 
+
 /**
- * Must obey the laws defined in cats.laws.ComonadLaws.
- */
+  * Comonad
+  *
+  * Comonad is the dual of Monad. Whereas Monads allow for the composition of effectful functions,
+  * Comonads allow for composition of functions that extract the value from their context.
+  *
+  * Must obey the laws defined in cats.laws.ComonadLaws.
+  */
 @typeclass trait Comonad[F[_]] extends CoflatMap[F] {
+
+  /**
+    * `extract` is the dual of `pure` on Monad (via `Applicative`)
+    * and extracts the value from its context
+    *
+    * Example:
+    * {{{
+    * scala> import cats.Id
+    * scala> import cats.Comonad
+    * scala> val id: Id[Int] = 3
+    * scala> Comonad[Id].extract(id)
+    * res0: cats.Id[Int] = 3
+    * }}}
+    */
   def extract[A](x: F[A]): A
 }