<@UG5HTPZ54> Natural transformations are defined a...

# arrow

[pakoito]

@Paolo Gavočanov Natural transformations are defined as FunctionK in Arrow

[Paolo Gavočanov]

yes, got that, I implemented the first example

[Paolo Gavočanov]

but I guess the For and Of stuff gets me confused

[Paolo Gavočanov]

is just much more straight forward to figure-out the signatures in scala/haskell for me ATM then in Arrow

[Paolo Gavočanov]

toying around with something like this, but gets me nowhere near atm 😕

object ImmutableKV : FunctionK<ForKVStore, ForState> {
        override fun <A> invoke(fa: Kind<ForKVStore, A>): Kind<ForState, A> {
            val op = fa.fix()
            return when (op) {
                is Put<*> -> StateApi.modify { mapK: MapK<String, Any?> -> mapK.updated(op.key, op.value) }
                is Get -> StateApi.inspect { mapK: MapK<String, Any?> -> mapK[op.key] as A }
                is Delete -> StateApi.modify { mapK: MapK<String, Any?> -> (mapK - op.key).k() }
            } as State<MapK<String, Any?>, A>
        }

[pakoito]

ank is our canonical example: https://github.com/arrow-kt/ank/tree/master/ank-core/src/main/kotlin/arrow/ank

[pakoito]

see if you can find the way around there. I cannot be more useful right now, I'm in another office working 😄

[Paolo Gavočanov]

np, thnx a lot for the direction 😉

[raulraja]

ank no longer uses Free

[raulraja]

Here is an actual example that uses Free https://github.com/arrow-kt/arrow/blob/master/modules/free/arrow-free-data/src/test/kotlin/arrow/free/FreeTest.kt#L22

[Paolo Gavočanov]

hey @raulraja, thnx for the pointer, been there, did my Id and Eq, having trouble with State, and I guess later on (from the cats article) with Inject.

[Paolo Gavočanov]

https://typelevel.org/cats/datatypes/freemonad.html#composing-free-monads-adts is where it gets interesting IMO with free monads, and that’s not covered by tests or docs in Arrow ATM, I guess it would be nice to add some docs/samples to Arrow once I figure it out.

[raulraja]

We have never bothered to get free and inject working because it would require injections manually since there is no implicits in Kotlin but keep87 would solve this

[raulraja]

Also inject +free is not a good idea since it degrades in performance as the number of algebras increases and requires special runtime optimizations like the ones we do in Scala

[raulraja]

http://frees.io/docs/optimizations/

[raulraja]

I would not recommend Free for architecture in Kotlin, just as.inyernal stack safe machinery or very simple programs

[Paolo Gavočanov]

yes, agree, I saw there is no FlatMapped and co. in Arrow, so all in all not ready for prime time in Kotlin, better do exploration in Scala ro Haskell

thnx a lot for your time guys!

[raulraja]

@Paolo Gavočanov I wrote this a while back https://www.47deg.com/blog/fp-for-the-average-joe-part3-free-monads/

[raulraja]

You can find the code in Scala and Haskell here too https://gist.github.com/raulraja/13a8a8789f9b70a1535ea4d44dfb1777

[raulraja]

in case it is of any help in your exploration around Free