Pure functional programming on android

Question

Are there any advancements in this area? I want to be able to write purely functional code on Android in Haskell or similar languages. I've tried some examples with Scala but it seems to be a pain to get started. Are there any other functional JVM languages which I can use to write Android applications?

Edit: functional languages that write native android applications. My mistake about the JVM.

Answer 1

I've never tried it personally, but you can do F# programming using Xamarin.Android (and, I believe, with Xamarin Forms too). You can see the guide here. (It also includes sample code).

As some background, F# is the .NET Framework's functional language. It is derived from ML; in fact, many ML scripts can be compiled almost "directly" as F# (with the caveat that you may have to do some renaming because F# has some additional keywords that ML doesn't have in order to support several .NET-specific extensions).

Xamarin allows for native development for Android, iOS, and Windows phone. Xamarin Forms allows for a single code-base for all three platforms (it's a competitor to Ionic).

One more quick point: Android does not use the JVM, even if you're writing apps in Java. (In fact, Android does not even support all Java 8 features yet). Through Android 4.4 it used Dalvik; after that, it started using Android Runtime.

You could also try using a JVM language like Scala to create a JAR file and create a bindings library for it.

Please also note that you'll end up using at least somewhat of a mixed paradigm - for example, things like Activities are objects, and the XML files used to define an Android screen is, for all practical purposes, declarative. Edit: This last point is slightly debatable - see the comments.

One final possibility: I haven't checked this out too closely, but try also this link for a site claiming you can do Scala in Android.

Answer 2

I you want a painless solution in terms of Gradle builds etc., you have only two options: Java and Kotlin, of which of course you should choose Kotlin ;)

Kotlin has most of the things you need to write in functional style:

• functions as first class citizen
• higher-order functions
• immutable collections
• var and val like in Scala
• if-else as a statement
• elements of pattern matching (where statement)
• tail recursion
• and more...

If you also include funKTionale and kotlinx.collections.immutable, you'll have all the functional goodies like: Option, Try, currying, memoization, persistent data structures and so on...

To start with Kotlin just install the latest Android Studio 3 Preview, which already has built-in Kotlin support.

BTW, don't be so polarized into "pure" functional ;) After all, being 100% "pure" means no side-effects, which means your app can't interact with the user ;)

Hope this helps :)

Answer 3

I doubt that you can find anything mature for writing Haskell-like code for Android. You do need to implement Java abstractions which are required by Android API (implement activity, etc.).

But if you really want to write for Android in a purely functional style you can try to implement your business logic in a pure functional language that compiles to JVM and call it from your Java classes. That approach would be much simpler than trying to implement it entirely in pure functional style.

As your language choice, you can try

• Frege, it even has a library for android - froid

• Eta lang, it is very new and probably nobody has tried to use it for Android yet