Addition derived combinators for Monad, Appliicative

[lukewyman]

Do we want to have any/all of the following derived combinators for cats structures such as Monad and Applicative?

def compose[A,B,C](f: A => F[B], g: B => F[C]): A => F[C]

def replicateM[A](n: Int, fa: F[A]): F[List[A]]

def filterM[A](as: List[A])(f: A => F[Boolean]): F[List[A]]

[adelbertc]

compose I think is handled by the Kleisli data type

filterM we have via MonadCombine

replicateA would be useful to have, i'm guessing on Applicative (maybe Traverse)

def replicateA[F[_] : Applicative, A](n: Int, fa: F[A]): F[List[A]] =
  List.fill(n)(fa).sequence

[lukewyman]

I took a shot at adding replicateA, as noted above, and immediately ran into the following compiler error:

/cats/Applicative.scala:35: could not find implicit value for evidence parameter of type cats.Traverse[List]

Since sequence is dependent on what type of collection the Traverse instance is for, it won't work on a concrete type like List

Is there another way I should try and implement this, or am I being naive in wanting to add this combinator?

[ceedubs]

@lukewyman I think import cats.std.list._ should make that compiler error go away.

[lukewyman]

...and indeed, it did. Thanks, @ceedubs.

[mikejcurry]

Should this one be closed now that #830 has been merged - or am I wrong and is there something left on it?

[ceedubs]

It sounds like all of these are taken care of except for filterM, which is being tracked by #1054, so I'm going to go ahead and close this out. Feel free to reopen if I've missed something.