johnhungerford

sealed trait Bool
object Bool:
    sealed trait True extends Bool
    sealed trait False extends Bool
    
sealed trait Nat
object Nat:
    sealed trait _0 extends Nat
    sealed trait Succ[N <: Nat] extends Nat

djspiewak

Understanding Comparative Benchmarks

I'm going to do something that I don't normally do, which is to say I'm going to talk about comparative benchmarks. In general, I try to confine performance discussion to absolute metrics as much as possible, or comparisons to other well-defined neutral reference points. This is precisely why Cats Effect's readme mentions a comparison to a fixed thread pool, rather doing comparisons with other asynchronous runtimes like Akka or ZIO. Comparisons in general devolve very quickly into emotional marketing.

But, just once, today we're going to talk about the emotional marketing. In particular, we're going to look at Cats Effect 3 and ZIO 2. Now, for context, as of this writing ZIO 2 has released their first milestone; they have not released a final 2.0 version. This implies straight off the bat that we're comparing apples to oranges a bit, since Cats Effect 3 has been out and in production for months. However, there has been a post going around which cites various compar

ChrisPenner

Optics By Example Cheat Sheets

The following are appendices from Optics By Example, a comprehensive guide to optics from beginner to advanced! If you like the content below, there's plenty more where that came from; pick up the book!

• Operators
• Composition Guide
• Substitution Guide
• Optical Constarints and Types

Operator Cheat Sheet

ChristopherDavenport

object RaceN {
  import cats.implicits._
  import cats.effect._
  import cats.effect.concurrent._
  import cats.data.NonEmptyList

  // Use with atleast 3, otherwise you should prefer Concurrent.race
  def raceN[F[_]: Concurrent, A](x1: F[A], x2: F[A], x3: F[A], xs: F[A]*): F[Either[NonEmptyList[Throwable], A]] = {
    for {
      deferred <- Deferred[F, A]

johnynek

package org.bykn.refmap

import cats.data.State
import cats.effect.Sync
import cats.effect.concurrent.Ref
import java.util.concurrent.ConcurrentHashMap

import cats.implicits._

/**

sellout

-- This illustrates (most of) a new(?) encoding of ad-hoc polymorphism using
-- dependent types and implicits.
--
-- Benefits of this approach:
-- • can have multiple “ambiguous” instances without requiring things like
--   Haskell’s newtypes to distinguish them;
-- • can disambiguate instances with minimal information, rather than having to
--   know some arbitrary instance name as you would with a system like Scala’s
--   implicits;
-- • implementers don’t need to know/provide the full family of instances – they

Daenyth

Concurrent resource caching for cats

Motivation

cats-effect Resource is extremely handy for managing the lifecycle of stateful resources, for example database or queue connections. It gives a main interface of:

trait Resource[F[_], A] {
  /** - Acquire resource
    * - Run f
 * - guarantee that if acquire ran, release will run, even if `use` is cancelled or `f` fails

notxcain

import cats.data.Kleisli
import cats.effect.{ Concurrent, Sync }
import cats.effect.concurrent.MVar
import cats.implicits._
import cats.{ Applicative, Functor, Monad }

// Let's start with our dsl

// First we need to interact with a console
trait Console[F[_]] {

SystemFw

// This is the traditional encoding, using abstract type members
// to encode existentials
object AbstractExistentials {
  trait E {
    type X
    val x: X
    def f(p: X): String
  }
   

neko-kai

package quantified

import cats.Monad

import scala.language.implicitConversions

/**
  * C[_] constraint applied to type F[_, _] quantified in first parameter, i.e.
  *
  * {{{