@benfleis The hidden Dragon is that the function is unsafe and nothing from it's type signature denotes that it's going to blow up if there are no elements. Safe versions of the same functions are:

import arrow.data.NonEmptyList

fun <A> NonEmptyList<A>.firstRest(): Pair<A, List<A>> =
  head to tail

fun <A> Iterable<A>.firstRest(): Pair<A?, List<A>> =
  firstOrNull() to drop(1)

a review of Clean Architecture: http://parametri.city/blog/2018-12-23-language-oriented-software-engineering/index.html

So a big question in my mind early on is how Kotlin will play with other languages in the FP world, firstly Clojure being JVM based, and Scala on up to Haskell and other native FP languages.

There is an entire conversation that is fairly recent about this same topic in #arrow

Any ideas?

how do I make a map like the following? it is the result of adding 2 maps together ....

mapA

is a

mapOf<String,AnsiColor>()

and

mapB<String,AnsiColor>

needs to be mapped from

set1<String>

in the way that

mapB

entries are constructed from

set1

String

element to

AnsiColor.GREEN

(this is a constant)

CompletableFuture.supplyAsync(Supplier<Boolean>{
                    true
                }, pool)

so if I want the

, pool

then I need to use

Supplier<>

? there is no way to get of it ? I'm asking because if you only supply one parameter then it is not necessary

you cannot have existentials in lambdas

you cannot have a lambda that’s generic for all <T>

Idle thought on Saturday: coming from Haskell, one thing that I'm missing in Kotlin is the let..in syntax Am I the only one that would like having something like this? (I've called it LETTING for clarity) A ideal constrain would be that the function should be pure, that is no access to external scope, like singletons, objects, public functions, java System. etc. etc.

A simplified example with Arrow Function1.contramap

Hey guys let me introduce myself and tell you why did I come in the first place: I'm 34, I have a small boy (15 months old!) and I've been developing software professionally for the last 4 years, mostly server side Java. I've been thinking what would be the best way to start learning FP since I started with Kotlin like a year ago. I'm always eager to learn and to improve my skills and knowledge. I couldn't find a trustworthy source to learn FP in Kotlin and given that Java is the language that I know the better and that Kotlin <- Java, I've bought the Functional Programming in Java book from Pierre Yves Saumont. Currently I've read half of the book. I've also been watching some videos from Kotlin, Arrow, 47 (I know some of you guys are here), category theory, etc. But it's a hard topic and I'm completely alone cause nobody knows what I'm talking about around me… Could you guys please shine a light on me? I mean, what do you think would be the best initial approach to learn FP effectively? What's in your opinion the best book/course to learn the fundamentals in Kotlin? I know about the red book of Scala but I would prefer to focus on Kotlin cause I really like it and I have real expectations of using it at work. So, where do you think is the best place to start practicing? Raul suggested me on Twitter that maybe I could contribute to some OSS so, how? Learn through pull requests? What do you tend to recommend to newcomers?

@Alex Welcome! There is https://arrow-kt.io/ in Kotlin for all your FP needs whther beginning data types like Option, Either etc or more complex abstraction like type classes and the Functor hierarchy all accompanied with a purely functional effects system where you can compose pure programs in Kotlin and learn about working with IO and dealing with side effects. https://arrow-kt.io/docs/effects/fx/ Swing by the #arrow-kt and #arrow-contributors channel and feel free to ask any questions or suggest how you’d like to get started. Most newcomers learn by pull request or simply ask question in those channels and people chime in helping out frequently with code snippets and links to materials for follow up. The arrow docs also include extensive tutorials such as : https://arrow-kt.io/docs/patterns/error_handling/ that teach you how to do error handling with FP all the way to building concurrent programs https://arrow-kt.io/docs/effects/fx/async/#parallelization--concurrency

Can you give a code snippet how you would do it?

but I'm not sure It is the best I can get

@thanh what is the goal you’re trying to achieve?

According to Kotlin coding conventions names of objects should start with an upper case letter and use the camel case (like classes), but you could also convert TVState to enum as it consists only of single-instance objects and then use uppercased letters.

is there a more functional way to write this code?

fun main(args : Array<String>) {
    val input = Scanner(System.`in`)
    while (true) {
    
      var currentMax =0;
      var iWithCurrentMax =0;
        for (i in 0 until 8) {
            val mountainH = input.nextInt()
            
            if(mountainH >currentMax){
               currentMax = mountainH;
               iWithCurrentMax = i;
            }
        }

        println(iWithCurrentMax) 
    }
}

Thanks, there's so many different ways to do the same thing. It can be a bit confusing actually

how to access Kotlin lambda in Java code?

For those interested in union types in Kotlin https://twitter.com/raulraja/status/1191142263273009152?s=19

Do you think that with the advent of arrow-meta Kotlin will become as good at functional programming as Scala? Or is there still something missing that Scala has but we don't? I'm trying to learn Scala and it's only now that I can fully appreciate the syntactic simplicity of Kotlin 😄

You are just specifying implicit conversions. They are proofs in the sense that any function is a proof by the curry-howard isomorphism, but such proofs aren't worth much in a language with bottom values since they are a proof of any type.

I want to handle exceptions in a

map

lambda by simply not mapping a value for when the exception happens? I"m currently adding

null

to the stream, then filtering out the nulls at the end. Is this the best and most idomatic way to handle this case?

fun parseList(strings: Collection<String>): List<Foo>
{
    return strings.stream().map { 
        try {
            parse(it)
        } catch (e: Exception) {
            null
        }
    }.toList().filterNotNull()
}

in Reactive Programming you should not store things out of the “chain”, if you want to sleep well on nights and avoid bizarre bugs related to dirty states

Hello, I am new to Kotlin and I would like to learn the concepts of functional and reactive programming, as well as Arrow. What books or resources do you recommend to learn? Thanks

Any chance to have something similar to an eta reduce in Kotlin?