Hi guys, one question, the typeclass compiler plug...

# arrow-meta

[bloder]

Hi guys, one question, the typeclass compiler plugin extension in arrow meta allows me to implement typeclasses like Keep 87 proposes?

[simon.vergauwen]

Similarly to KEEP 87 yes.

There are a couple of small differences, for example the call-site syntax currently used in the typeclasses prototype plugin.

fun doSomething(TT: Traverse<ForIO> = `with`): IO<Unit> =
  listOf(1, 2, 3).traverse { i ->
    IO.effect { println("Hello $i") }
  }.unit()

[rcd27]

@simon.vergauwen will it change arrow-kt syntax? For example now all is wrapped in Kind<T,V> type. Will it "unwrap" to T<V>?

[simon.vergauwen]

It will allow you to write T<V> instead of Kind<ForT, V> but it doesn’t require you to do so 🙂

[simon.vergauwen]

The plugins are opt-in.

[simon.vergauwen]

What we do with the `Kind`s for example is co-operate with the TypeChecker so that Kind<ForT, V> == T<V> but the generated code is the same as it is now. We can hide it from the user using a compiler & IDE plugin.

So we basically put some syntactic sugar on top of the current impl.

[bloder]

@simon.vergauwen nice! thank you! Is there any example of an implementation of typeclass?

[raulraja]

They have the same shape as all typeclasses in arrow but you can check out the compiler plugin tests in meta for an example

[bloder]

Thank you!

[Bob Glamm]

It's too bad the syntax couldn't be implicit TT: Traverse<IO> 😄 🧌