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@Daenyth
Daenyth / MonadAndFs2Ops.md
Last active June 25, 2024 13:04
Cheat sheet for common cats monad and fs2 operation shapes
Operation Input Result Notes
map F[A] , A => B F[B] Functor
apply F[A] , F[A => B] F[B] Applicative
(fa, fb, ...).mapN (F[A], F[B], ...) , (A, B, ...) => C F[C] Applicative
(fa, fb, ...).tupled (F[A], F[B], ...) F[(A, B, ...)] Applicative
flatMap F[A] , A => F[B] F[B] Monad
traverse F[A] , A => G[B] G[F[A]] Traversable; fa.traverse(f) == fa.map(f).sequence; "foreach with effects"
sequence F[G[A]] G[F[A]] Same as fga.traverse(identity)
attempt F[A] F[Either[E, A]] Given ApplicativeError[F, E]
@kiambogo
kiambogo / groupBy.scala
Last active September 22, 2020 00:01
FS2 1.0.0 groupBy
import fs2.concurrent.Queue
import cats.implicits._
import cats.effect.Concurrent
import cats.effect.concurrent.Ref
def groupBy[F[_], A, K](selector: A => F[K])(implicit F: Concurrent[F]): Pipe[F, A, (K, Stream[F, A])] = {
in =>
Stream.eval(Ref.of[F, Map[K, Queue[F, Option[A]]]](Map.empty)).flatMap { st =>
val cleanup = {
import alleycats.std.all._