cats VS Ammonite-Ops

Compare cats vs Ammonite-Ops and see what are their differences.


Lightweight, modular, and extensible library for functional programming. (by typelevel)


Scala Scripting (by lihaoyi)
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cats Ammonite-Ops
43 15
5,086 2,575
0.5% 0.1%
9.1 7.4
1 day ago 8 days ago
Scala Scala
GNU General Public License v3.0 or later MIT License
The number of mentions indicates the total number of mentions that we've tracked plus the number of user suggested alternatives.
Stars - the number of stars that a project has on GitHub. Growth - month over month growth in stars.
Activity is a relative number indicating how actively a project is being developed. Recent commits have higher weight than older ones.
For example, an activity of 9.0 indicates that a project is amongst the top 10% of the most actively developed projects that we are tracking.


Posts with mentions or reviews of cats. We have used some of these posts to build our list of alternatives and similar projects. The last one was on 2023-07-05.
  • Beware of teammates who refactor code based on personal taste without proper documentation or completeness. Sounds familiar.
    2 projects | /r/programming | 5 Jul 2023
    A functional programming library:
  • Is Scala worth learning in 2023?
    5 projects | /r/scala | 29 Jun 2023
    Learn something that pays the bill first - nowadays it's Golang/Rust react/typescript. Then you can try some pure fp libs like fp-ts and, and look through existing scala cats docs. If you'll feel bad about it - that's totally fine and expectable, fp takes a paradigm shift and not that many dev able to shift their brains way of thought due to basic psychological rigidity) (inability to change habits and to modify concepts/attitudes once developed). And that's purely a staffing and management issue - folks hired randoms out of the blue, and called 'em a team.
  • Going into year 2 of Software Development Foundation Degree, have a particular liking for OOP and SQL, any tips, info or pointers on where to go from there?
    2 projects | /r/cscareerquestions | 29 May 2023
    I'm sorry, but have you ever done functional programming for a real company, like in a functional programming language like Haskell, Scala, or F#? Have you ever used Scala cats or scalaz? Have you ever learned category theory and how to apply its abstractions in software? Listen u/judethedude2106 this person hasn't gone as far down the functional programming rabbit hole as I have. Beyond learning the basics like the difference between pure and impure functions, what are closures, what higher order functions are and the most common ones like .map, .filter, and .flatmap, the immutable collections like immutable linked lists and trees, and what a Monad is and common monads like those used for futures/promises, async programming, and Option (Some or None, which is used instead of null checking), the more advanced functional programming stuff like category theory based abstractions are totally useless for real jobs and is just a giant time suck. Don't waste years on functional programming, spend at most a few months on it and no more.
  • rsmonad: Monads in stable Rust (+ Applicative, Alternative, Functor, Monoid, ...)
    2 projects | /r/rust | 24 May 2023
    As a former functional programmer in Scala, please do not go deep into the Category Theory programming. Scala has libraries like this one called "Cats", a cute shortened name for "Category Theory", but code that makes heavy use of these constructs is not understandable to other programmers. Other than using Monads as a design pattern for things like Options (which can be "Some" or "None"), Futures or Promises (which is used for asynchronous programming), and a few other things, please do not make heavy use of category theory constructs in real programming projects that will have other developers working on them. It is a rabbit hole that may be fun but is not super practical. Sure, write pure functions without side effects, but do not use the words "Bimonad", "Invariant Monoidal", and "Semigroup" in your code. The most common, practical application/use of functional programming is basic things like closures, .map, .filter, maybe chaining maps with like a .flatmap or whatever your programming language uses instead of chain or flatmap, and SQL that uses keywords like WHERE which can be represented in code by using a call to .filter. Like the place where these constructs are used most is in data processing like with SQL, ETL (Extract Transform, Load) jobs, Java's MapReduce on Hadoop, Scala's Apache Spark, and other data processing type things. Haskell is not a popular programming language in real world projects for a number of reasons and one of them is the heavy and sometimes impractical use of Category Theory.
  • Tmux, NeoVim, etc. to write pure Kotlin code?
    2 projects | /r/Kotlin | 30 Apr 2023
    At a previous job of mine we actually had an entirely pure Scala ecosystem using cats which instead uses typeclasses, referential transparency, and other FP concepts as the foundations for how to code. So a lot of flexibility to the language.
  • [E => *] Type
    2 projects | /r/scala | 9 Mar 2023
    Thanks! It's used heavily here
  • for comprehension and some questions
    3 projects | /r/scala | 22 Jan 2023
  • Ask HN: How has functional programming influenced your thinking?
    4 projects | | 16 Jan 2023
    I did work in Scala for a few years. We employed Cats[1], and even a bit of Matryoshka[2] though most of the work I do today is in Python.

    Nowadays I think about computational requirements in terms of relations among behavioral dependencies. Like, "I want to perform operation O on input A and return a B. To do this, I'll need a way to a -> b and a way to b -> b -> b." I often pass these behavioral dependencies in as arguments and it tends to make the inner core of my programs pretty abstract and built up as layers of specificity.

    Zooming out nearly all the way, it makes me feel tethered in a qualitatively unique way to certain deep truths of the universe. In a Platonic sense, invoking certain ideas like a monad make me feel like I'm approaching the divine or at least one instantiation of a timeless universal that operates outside of material existence.

    I'd imagine some mathematicians might see the universe in a similar way - one where immortal relations between ontological forms exist beyond time and space and at the same time can be threaded through the material world by intellectual observation and when those two meet a beautiful collision occurs.



  • yet another post about type classes in Scala
    2 projects | | 2 Jan 2023
    Our second type class example attempted to illustrate one last perk: type safety at compile time. It did so with a simplified example of the cats core library for type safety equality comparison between objects. If you're not familiar with cats, go ahead and give it go.
  • Which functional programming language should I learn?
    5 projects | /r/functionalprogramming | 28 Oct 2022
    3) Finally, Scala 3 + cats is a great middle ground. It's a great language to teach and learn FP, even if you learn by yourself, without support from other people. There are lots of materials and even if you get stuck with a concept, you can still implement it using what you knew before.


Posts with mentions or reviews of Ammonite-Ops. We have used some of these posts to build our list of alternatives and similar projects. The last one was on 2022-09-13.
  • Scala Isn't Fun Anymore
    9 projects | | 13 Sep 2022
    That's funny, because this is what I really like about Scala; how quick and easy it is to get a project started.

    > sbt new scala/scala3.g8

    will just create an empty project. If you don't even want to bother with a project, use use scala-cli or ammonite ( to just start banging out code.

    Even the upgrading of a project from Scala2 to Scala3 is a breeze, thanks to very good backwards compatibility of new library releases.

  • A Python-compatible statically typed language erg-lang/erg
    27 projects | | 13 Aug 2022
  • Scala 3 Reflection
    5 projects | /r/scala | 1 Feb 2022
    Scripting API is quite limited, so the third option. - reuse the ammonite scripts or look how this is implemented (using internal compiler API),
  • Audacity Fork Without Any Sentry Telemetry or Crash Reporting
    9 projects | | 5 Jul 2021
    Here's an example of a smaller project that added telemetry without suffering a fork:

  • Scripting with Java – Improving Approachability
    2 projects | /r/java | 12 May 2021
    Or ammonite - I've ran Gatling performance test from a simple script based on this gist it fetches all the dependencies, compiles and runs the test, producing nice html report..
  • 25 years of OCaml
    3 projects | /r/programming | 10 May 2021
    Scala with the Typelevel ecosystem. Stay on the jVM, but have a much more pleasant and robust experience, including a great REPL.
  • The Scala ecosystem and circular dependencies?
    3 projects | /r/scala | 10 Apr 2021
    If you are installing, and you are learning, I would also recommend ammonite as an easier REPL.
  • IPython as a System Shell
    3 projects | | 6 Apr 2021
    I've been using amm on and off

    pretty nice if you know scala, still have to use regular shell(s) so I do not forget them

  • A Lisp REPL as my main shell
    5 projects | | 8 Feb 2021
    I've never tested Ammonite, only read the, so I'm only guessing here.

    From what I understand, Ammonite was designed as a "readline shell" as I wrote in the article. It perpetuates this approach that everything is a command.

    The thesis of my article suggests we do the opposite: I'm suggesting to rethink shells by starting from the interface (here the SLY REPL) and then implement the shell features.

    In particular, it seems that Ammonite does not support back-references and I'm not sure it has an interactive inspector.

    While Ammonite seems to be a definite improvement over the _syntax_ of Bash, etc., I'm not sure it brings much novelty in terms of user interface. But again, I know very little about it so I may have missed some features :)

    5 projects | | 8 Feb 2021
    I wonder what people think about Ammonite (

    It's not Lisp but Scala so may not be the authors language of choice however it can be used as a Shell:

    I am personally using it and compared to a classical shell like Bash it's really nice for more structured data related tasks (exploring some API, checking some data, creating a bunch of PRs at once, ...).

    It also makes use of Scala's adjustable syntax and functional concepts so you basically get shell piping but in a strongly typed fashion (e.g.

What are some alternatives?

When comparing cats and Ammonite-Ops you can also consider the following projects:

Scalaz - Principled Functional Programming in Scala

Shapeless - Generic programming for Scala

ZIO - ZIO — A type-safe, composable library for async and concurrent programming in Scala

ScalaTest - A testing tool for Scala and Java developers

Monocle - Optics library for Scala

better-files - Simple, safe and intuitive Scala I/O

Scala Async - An asynchronous programming facility for Scala

Quicklens - Modify deeply nested case class fields

calculator - Windows Calculator: A simple yet powerful calculator that ships with Windows

Scala Graph - Graph for Scala is intended to provide basic graph functionality seamlessly fitting into the Scala Collection Library. Like the well known members of scala.collection, Graph for Scala is an in-memory graph library aiming at editing and traversing graphs, finding cycles etc. in a user-friendly way.