I would just like some language options on where to start my learning of Functional Programming.
I've been developing since the Commodore 64 days with a focus on C, C++, Java, and C#.
Thanks!
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Keep in mind while learning FP, that (according to me at least) the most important guideline is to use pure functions as much as possible. That's how you get the maintainability benefits out of FP. Most of the rest of the functional programming patterns are just to support using pure functions. I have a more detailed post about that here. If you just use the patterns without pure functions its not going to get you much over other paradigms. Language suggestions:
Elm will force you to write pure functions. But it is a language/platform focused solely on (web) UI. If you have a project in mind targeting the web, this would be the route to go IMO. Download a high rated starter project so you don't have to get lost in the weeds setting up the build/dev environment. I also highly recommend Semantic UI (just the CSS) for GUI elements.
F# is my favorite. But since it has no distinction between pure and impure functions, it doesn't condition you as heavily into using pure functions. You can always fall back to imperative if a pure solution is elusive. I started with F#, and I feel like this led me to miss the point of FP for a while. (I was focusing on using functional patterns instead of writing pure functions.) But I think it is a great general-purpose FP language, because you can choose to go imperative in performance-critical parts. F# can call C# code and vice versa with no FFI.
OCaml is another option, and F# is based on it.
Haskell will also force you to use pure functions, but is much harder to break into (IMO) due to its complex type system and lots of operator symbols to learn. I'll mention Eta here too, as it is basically Haskell for the JVM.
Clojure is an interesting one. It's a Lisp dialect and dynamically typed so its FP flavoring is a bit different in general. I've heard it said that in Clojure (like Lisp) you write the code that writes the code to solve the problem.
Aside: I hate couching things in terms of purity and impurity... both types of functions are needed for any useful program. But historically those are the terms used in this context. A pure function is really just another name for a deterministic function.
Great rundown, if you're interested in something new and interesting, check out Reason, and slightly more mature, Elixir language. Elixir is built on the Erlang VM, but has a lot of inspiration ideological inspiration from Ruby.
Thanks. I knew I would forget some. :)
Note that Reason is just a Javascript-like syntax on top of OCaml. My pref would be to use the OCaml syntax, but dealer's choice.
Another +1 for Elixir here. It's fantastic!
What's a "pure function"?
It's a function that computes the same value, every time you call it with the same arguments, and depends only on those. The value can not depend on time or any mutable state outside of it.
It also can not have any side effects, like throwing exceptions or printing to the console.
This has a lot of benefits for reasonability, testability and compiler/runtime optimization, but can sometimes lead to code that's painfully explicit.
Especially if coming from Java, I can recommend Scala.
There is a great course on coursera.org/learn/progfun1, taught by the creator of Scala, Martin Odersky.
I recommend Functional Programming in Scala
I read Japanese version of It and did many of exercises.
You can learn "Recursive function","Pure function","Algebraic data type","Monad", and many other concepts of functional programming by this book.
Some of exercises are difficult to solve. But many of them are very good exercises like puzzle.
After reading this book, I think you will be able to understand many of topics of functional programming.
If you're looking for practical experience that you can use in your current projects, then look towards the functional aspects of your current language. Functional programming is a paradigm, it does not define a language.
You are looking to using the high-level constructs like pure functions and high-order functoins. You want to learn about immutable data structures, recursion and things like lambdas and closures.
JavaScript, Python, and NodeJS, among those I know, all offer a good assortment of functional programming constructs. C++ does as well, but it's syntax can be a bit daunting. I'd likely start with Python since I've seen people use it's functional aspects to wonderful effect while coding (during interviews I've done).
For me, it seems Python is an odd choice to learn functional programmming. I've recently picked it up for a project, and I do my best to use it in a functional way, but it keeps throwing obstacles. For example, the 2 primary data structures, lists and dictionaries are mutable.
There is a package called toolz that helps quite a lot, but compared to something like ramda for Javascript, it feels very shallow and without a clear concept.
It's main mode of failure also seems to be exceptions, which kind of makes it harder.
Why do you think it's a good starting point?
I said for practical experience. If you're already using Python on a project you can start learning functional constructs in your actual code.
Paradigms are only useful in combination with other paradigms as well, so it's good to learn how to use them together. In this case it's also helpful to learn the concepts when presented with a language that isn't strict about its constructs.
Exceptions are totally fine in the functional paradigm. Some languages choose to use Monads instead, but nothing about exceptions breaks the functional model. In my experience monads are more confusing, and less helpful than an implicit error model.
I think we're talking about different things here. To be clear, I absolutely agree that functional programming concepts can be applied to any other language that does not feature it as one of their strongest paradigms. An generally, it's a good idea to do that to some degree, highly dependent on general language idioms.
In order to learn those concepts though I would recommend going for a language where those concepts are somewhere between important and fundamental. And that includes fundamental concepts like Monads, ADTs and referential transparency.
Whether exceptions are fine or not within FP really depends on the definition of both. I've seen monads being overused and annoying, but I've also seen them restoring maintainability for large codebases. For asynchronous code, they are very valuable.
I recommend Elixir for you. I started to learny it a few weeks ago and it's been a lot of fun.
The best book about this: amazon.com/Programming-Elixir-1-3-...
There are lots of functional programming languages to choose from. The "best" one depends on your interests.
Since you have used C#, you have familiarity with .NET. I presume you have Visual Studio or Xamarin IDE on hand.
F# ought to be a good choice.
I've read a lot of F# books. The one I recommend to get your bearings with F# is The Book of F# by Dave Fancher.
In my opinion, it is a really good book for F# as a tutorial and hand-holding book. Different people learn in different ways, and this book fit very well with my learning style.
When I learned F#, I used Xamarin and Mono, on Macintosh. But I have experience with Visual Studio as well, and F# is definitely a first-class language in the .NET ecosystem.
You might want to give Perl6 a try. Although it's not purely functional, it does have the full range of functional structures. Plus you can do things procedurally if you want to. It's a great language, anyway.
This could be a guided start (in Scala):
scala-exercises.org/fp_in_scala/ge...
There, the FP concepts are explained through Scala, so you can take the specific Scala syntax related too, if you need to.
I dived heads first (no prior FP experience) into Haskell and I love it. "Learn you a Haskell" and "Real world Haskell" are great online resources to get you started.
The point I like the most about Haskell, is that it has a small core. It is not some syntax sugar abomination like C++ and more recently Javascript.
Every new extension added is still desugared to this small core. Plus, type classes are just amazing.
I was going to suggest a Haskell MOOC, so I'll start by saying think Haskell is suitable for learning the core concepts :)
I would recommend Introduction to functional programming. The course is loosely based around Graham Hutton's book Programming in Haskell.
Once you've learned the core concepts it should be easy to switch to another language that may be applicable in your field of development.
I think FP is a broad field and like OOP every language has its own idea how to do it right.
Haskell and PureScript for example feel to theoretical to me, with co-monads, lenses, pro-functors and what not...
OCaml on the other hand feels more approachable, but I don't really know why. All I can say that I don't feel bombarded with theoretical concepts when reading about it...
I would definitely recommend Elixir, as it is getting very popular. It's probably already the most popular functional language.
Take a peek at Elixir, it's a fantastic language with a great community behind it willing to answer any and all questions!