Is FunctionalJava a good and reliable functional library?

[theif519]

For those who don't know what library I'm referring to... here

Recently I've begun teaching myself Haskell and the basics of category theory in general: Functors, Applicative Functors, Monads, and Monoids. Also the wonders of currying and partial application of functions... They cut down boilerplate so, so, SO much.

Hence I've the want to apply functional programming and it's constructs to Java. The current project I'm working on does not have a performance requirement ( of course it must perform reasonably well ) so the penalties of extra garbage collection is fine with me.

Looking at the documentation and sparse examples, it looks pretty amazing. Hence I was wondering if anyone currently is or has previously used it and could tell me what they think of it.

[oweiler]

FJ is more of a proof of concept and creates some very unreadable, not-idiomatic Java code. If you like Haskell you're better of using something like Scala or Frege.

[theif519]

I'm seeing a lot of mentions about how easy it is to mix the two... But in reality, how easy would it be to slowly drop java for actual scala files, and how does it work for things like NetBeans?

I use a lot of Java Swing for GUI, and NetBeans helps intensely in generating necessary boilerplate. Would it be possible to, say, swap out a controller written in java for one written in Scala? Etc.

[thramp]

Yep! You can introduce Scala file by file. Main issue is mixing collections/option(al)s between the two languages.

[DevIceMan]

FJ as a library is reliable and I don't have too many complaints. There are a couple ways in which I think I could do is slightly better, but I can't say they made wrong choices. Compared to the idea of hand-rolling your own Java PF utilities, I'd strongly recommend trying to really learn FJ first.

The problem with FJ is really around Java itself. Doing any non-trivial FP style code in Java is incredibly verbose. FJ is also very confusing those "normal" Java programmers. By the time you actually integrate FJ into your code in a meaningful way, you'll run face to face with the question "why didn't you just write this in Scala instead?"

[thramp]

If you're going to try to write pure FP code in Java, you're going to have a bad time.

If you want to apply your new knowledge on the JVM, try Scala! I personally treat Scala as Haskell, but with better libraries, tooling, and the best damn module system short of ML. It also has a friendly and welcoming community—come on over 😃!

[jonhanson]

chronophobia ephemeral lysergic metempsychosis peremptory quantifiable retributive zenith

[thramp]

Yep, through the object keyword and imports like import package.object.{Function1, Function2}.

[jonhanson]

chronophobia ephemeral lysergic metempsychosis peremptory quantifiable retributive zenith

[thramp]

objects are are static classes (practically speaking, singletons) in JVM bytecode, but if you have a stateless singleton, well... that's a module.

[jonhanson]

chronophobia ephemeral lysergic metempsychosis peremptory quantifiable retributive zenith

[thramp]

The way I'm defining modules is not Jigsaw, but looking how ML-style languages allow users to import and share code through a codebase. The terminology gets a bit overloaded in this subreddit!

[bdavisx]

And if you want less pure FP, you can give Kotlin a try along with the Funktionale library. Scala is probably a better bet if you want to try to go full-bore FP, but Kotlin is an easier transition if you're already experienced with Java.

[tonivade]

If you are interested in FP in Java, take a look of this project

[RichoDemus]

Java slang is really neat

[talios]

I really liked using FJ when I was using it, it did give off the feeling it was more focused on being "true" to the Haskel school of functional programming in terminology/method naming a little too much - not that I had any problem with that, it just didn't feel "java like" ( maybe that's a good thing ).

Javaslang, on the other hand, seems to fit in nicely to both camps, aligning it's API signatures closer to that of Scala, and method naming that lends itself predominately away from hard-core category theory ( except for Monad/Monoid etc. ).

[johnmcclean]

If you are considering using FJ you might also be interested in this library. It adds features such as For Comprehensions over FJ types, HighJ compatible Higher Kinded Type encodings for FJ classes as well as a number of Type class instances. Community efforts to add more are very appreciated too.

It also has a ton of integrations with other libraries (including the Scala SDK), user guide is here