Scala Cats

Open-source Scala projects categorized as Cats | Edit details

Top 21 Scala Cat Projects

  • GitHub repo Scala Exercises

    The easy way to learn Scala.

    Project mention: What should I avoid coming from Java to Scala? | | 2021-08-19

    Hahaha, I know when people ask for advice everyone throws in a book. But honestly, this one is the main "learn scala" book, and it's got a lot of examples so it's not as dry as the rest. Also there's a website where the examples can be done and validated in the browser:

  • GitHub repo Http4s

    A minimal, idiomatic Scala interface for HTTP

    Project mention: Akka became the de-facto solution for Scala web development? | | 2021-09-18


  • Scout APM

    Scout APM: A developer's best friend. Try free for 14-days. Scout APM uses tracing logic that ties bottlenecks to source code so you know the exact line of code causing performance issues and can get back to building a great product faster.

  • GitHub repo Monix

    Asynchronous, Reactive Programming for Scala and Scala.js.

    Project mention: Alternative to RxJava/RxScala | | 2021-02-08

    The Observer is a bit different, it returns Future[Ack] for built-in back-pressure. We can Continue / Stop synchronously or asynchronously.

  • GitHub repo Monocle

    Optics library for Scala

    Project mention: Monocle 3 release candidate - a super useful and simple library for optics with poetic api | | 2021-06-01

    See example

  • GitHub repo sttp

    The Scala HTTP client you always wanted!

    Project mention: Scala newbie hoping to understand sttp with tapir testing. | | 2021-08-04

    Assuming stub here is an SttpBackendStub, I can't see any machinery that would result in a NotFound when the whenRequestMatches isn't satisfied. So as /u/DrGrimmWall says, I think we need more information in order to be able to help.

  • GitHub repo scala-pet-store

    An implementation of the java pet store using FP techniques in scala

    Project mention: Do you have someone experienced with Flutter and Scala? What is your stack, and what do you think about this? | | 2021-09-20
  • GitHub repo pfps-shopping-cart

    :shopping_cart: The Shopping Cart application developed in the book "Practical FP in Scala: A hands-on approach"

    Project mention: Functional Programming in Scala book suggestions | | 2021-10-12
  • Nanos

    Run Linux Software Faster and Safer than Linux with Unikernels.

  • GitHub repo Mockito Scala

    Mockito for Scala language

  • GitHub repo monadless

    Syntactic sugar for monad composition in Scala

    Project mention: Kind: A Modern Proof Language | | 2021-08-11

    Well `RecordWildcards` has been around for 14 years... but even without it instead of `{..}` you'd just have `_`s. The main thing that is different is that your Kind example had nested case statements while your Haskell example tried to match everything on one shot, which makes for a non-equivalent comparison.

    > Not sure how that could work, though. Idris had an interesting syntax, but IIRC it wasn't general.

    I assume you're talking about idiom brackets for applicatives? The general syntax is given in something like The idea is to basically take async-await syntax and generalize it to any monad.

    So e.g. your `Maybe` example (using `!` for the equivalent of `await` for concision) would look like

      Maybe {

  • GitHub repo natchez

    functional tracing for cats

    Project mention: Question on implementing open tracing with Scala Futures | | 2021-07-01

    It's never going to work with a ThreadLocal-based implementation because Future (and other Scala async stuff like cats.effect.IO) hop from thread to thread in an unpredictable way. The only way to do it is to jettison the magical "current span" thing and pass the span explicitly. You can hide this in the plumbing if you program with abstract effects (this is what Natchez Trace does) but with Future I think you're going to have to pass everything around in the open.

  • GitHub repo Iteratee

    Iteratees for Cats

  • GitHub repo Pulsar4s

    Idiomatic, typesafe, and reactive Scala client for Apache Pulsar

  • GitHub repo Octopus

    Scala library for boilerplate-free validation (by krzemin)

  • GitHub repo pfps-examples

    :izakaya_lantern: Standalone examples shown in the book "Practical FP in Scala: A hands-on approach"

    Project mention: Scala FP code samples | | 2021-01-22

    You may want to check pfps-shopping-cart as well as the book that covers the step by step of how to build such application (the github repo contains a link). Also, that book also has a couple of examples that you can find here.

  • GitHub repo Scala Test-State

    Scala Test-State.

    Project mention: What's the maturity level of ScalaJS? | | 2021-08-27

    It actually been rock-solid for many, many years now! I've built quite a few things with it and introduced it to teams who picked it up very quickly and with no major problems. I've never had any production problems with it EVER and I've been living and breathing it pretty much every day for ages now. It's very, very unit testable (oh! check out Scala Test State if you're interested in really powerful and concise Scala.JS testing) so it's nearly trivial to have to very well tested webapp, including mouse clicks, key presses, whatever you want. Awesome awesome stuff and the Scala.JS team deserve some kind of tech Nobel prize imo. It's been a game changer for me.

  • GitHub repo cats-effect-testing

    Integration between cats-effect and test frameworks

    Project mention: Are there really 'testing benefits' to programming with effects? | | 2021-01-19

    cats-effect-testing covers Specs2, ScalaTest, uTest, and minitest.

  • GitHub repo fs2-data

    streaming data parsers and manipulation library

    Project mention: How do I process gigabytes size file? | | 2021-08-01

    If it's a CSV file look at fs2-data.

  • GitHub repo xs4s

    XML Streaming for Scala including FS2/cats support

  • GitHub repo pencil

    Simple smtp client (by minosiants)

    Project mention: Pencil is a scala smtp client | | 2021-01-19
  • GitHub repo free-arrow

    Implementation of the Free Arrow in Scala and other helpful tools for working with Arrows

    Project mention: Pure Functional Stream processing in Scala: Cats and Akka – Part 1 | | 2021-02-07

    Interesting post, although the use of `cats.IO` feels a little shoehorned. I've found some nice cats/akka synergy by abstracting over flows using a `cats.arrow.Arrow` instance for ``. That might be just as shoehorned though, since I haven't yet worked out whether akkas `Flow` forms a lawful Arrow

  • GitHub repo iron-cats-example

    An example project using Iron & Cats

    Project mention: Building a REST API in Scala 3 using Iron and Cats | | 2021-07-27

    We've seen in this tutorial the extreme readability of our small API offered by Iron and Cats can consult the code and test instructions of the finished example on

NOTE: The open source projects on this list are ordered by number of github stars. The number of mentions indicates repo mentiontions in the last 12 Months or since we started tracking (Dec 2020). The latest post mention was on 2021-10-12.


What are some of the best open-source Cat projects in Scala? This list will help you:

Project Stars
1 Scala Exercises 2,406
2 Http4s 2,110
3 Monix 1,807
4 Monocle 1,420
5 sttp 1,156
6 scala-pet-store 882
7 pfps-shopping-cart 328
8 Mockito Scala 266
9 monadless 235
10 natchez 234
11 Iteratee 188
12 Pulsar4s 181
13 Octopus 142
14 pfps-examples 136
15 Scala Test-State 127
16 cats-effect-testing 110
17 fs2-data 64
18 xs4s 49
19 pencil 33
20 free-arrow 14
21 iron-cats-example 3
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