kotlinlang #functional

The associated repo demonstrate how a stack safe DSL can be built a top Free Applicatives completely decoupling the DSL declaration from it's interpretation and opening the door for users to provide new interpreters and extend the DSL

Jorge Castillo

11/11/2017, 12:38 PM

About Monad Transformers as a way to make your monad stack simpler when working on Functional Programing architectures using Kategory. All the feedback is more than welcome 😉. Thanks in advance! https://medium.com/@JorgeCastilloPr/kotlin-functional-programming-ii-monad-transformers-b1f020f14dd8

🤖 2

👏 5

pakoito

11/16/2017, 10:31 AM

It is ooout: Intro to Kategory

pakoito

11/16/2017, 10:31 AM

https://www.youtube.com/watch?v=IL5XzaCMKpQ▾

👏 6

👍 5

🎉 5

🎬 2

raulraja

11/21/2017, 1:38 AM

http://chrispenner.ca/posts/free-forgetful-functors

raulraja

12/08/2017, 3:07 AM

I have free tickets for scala exchange in London if anyone is in the area and interested to attend. A lot of FP will be discussed and interesting ideas we can bring to FP in Kotlin.

raulraja

12/08/2017, 3:09 AM

Looking forward to meeting more people in the Kotlin FP community

dh44t

12/22/2017, 9:47 AM

Hi guys, a little bit of spam today

dh44t

12/22/2017, 9:47 AM

https://www.packtpub.com/application-development/functional-kotlin

raulraja

01/13/2018, 2:01 AM

https://www.microsoft.com/en-us/research/blog/functional-programming-languages-pursuit-laziness-dr-simon-peyton-jones/

raulraja

01/15/2018, 3:19 PM

https://twitter.com/raulraja/status/952919513875603456

K 7

arrow 7

helpermethod

01/17/2018, 10:05 AM

Hi, I have some question regarding FP in Kotlin

helpermethod

01/17/2018, 10:05 AM

Most of my functions are top-level funs which only rely on their input params

helpermethod

01/17/2018, 10:06 AM

For dependencies, I pass in function parameters

helpermethod

01/17/2018, 10:06 AM

So this seems to work pretty well

helpermethod

01/17/2018, 10:07 AM

But now I have a bunch of functions which all need to use a Java object for retrieving stuff via reflections. I've put them into their own file and the functions are all using the same instance. It doesn't look very FPish but I have no idea how to best solve that problem 😞.

helpermethod

01/17/2018, 10:09 AM

Copy code

private val reflections = Reflections()

fun getRouterName() =
	reflections
		.getTypesAnnotatedWith(MCMain::class.java, false)
		.first()
		.simpleName

fun getElements() =
	reflections
		.getTypesAnnotatedWith(MCElement::class.java)

fun getChildElements(type: Class<*>) =
	getAllMethods(type, withAnnotation(MCChildElement::class.java))

fun getSubTypes(type: Class<*>) =
	reflections
		.getSubTypesOf(type)
		.filter { it.isAnnotationPresent(MCElement::class.java) }

raulraja

01/17/2018, 10:29 AM

@helpermethod if your model is reflection I think that is a fine API except for one thing: -

first()

is an unsafe api and it may blow up, you should probably use

firstOrNull

which is safe:

Copy code

data class RouterName(val name: String)

fun getRouterName(): Option<RouterName> =
    Option.fromNullable(
      reflections
        .getTypesAnnotatedWith(MCMain::class.java, false)
        .firstOrNull()
    ).map { RouterName(it.simpleName) }

I would add explicit return types since they seem to be public functions. Normally you can call it functional if: - Given an input it always produces the same output (functions are pure) - Does not use global mutable state - Does not modify the outer state - Side Effects are encapsulated in functions or data types that allow deferring their execution

👍 1

helpermethod

01/17/2018, 12:22 PM

@raulraja Thanks for your help, I will consider your improvements

👍 1

helpermethod

01/18/2018, 10:24 AM

Hi, regarding functional error handling. Say if an error occurs I want the program to stop. With exceptions I just don't catch the exception and let it propagate. But how do this with Either<Left, Right>?

lupajz

01/18/2018, 11:02 AM

.fold({ throw some exception }, { .. continue with right })

could work ?

simon.vergauwen

01/18/2018, 11:13 AM

If you are chaining operations with

flatMap

or monad bindings then it short circuits on failure.

👍🏽 1

simon.vergauwen

01/18/2018, 11:15 AM

So you could indeed re throw the exception with

fold

or handle in any other way you desire like showing user a message.

raulraja

01/18/2018, 11:56 AM

@helpermethod we also have http://arrow-kt.io/docs/patterns/error_handling/ in case you have not come across it yet.

raulraja

01/18/2018, 11:56 AM

It shows different approaches to FP error handling with

Option

Try

Either

and

MonadError

and comparing them to throwing exceptions.

helpermethod

01/18/2018, 1:02 PM

Does rethrowing not break referential transparency?

simon.vergauwen

01/18/2018, 1:54 PM

I meant if you reach the edge of your system you need to deal with the result. For an annotation processor or gradle task throwing an exception could be a valid way to give feedback to the user that something went wrong.

simon.vergauwen

01/18/2018, 2:05 PM

@simon.vergauwen uploaded a file: Untitled

-.kt