If I want to fold with a curried suspend function, what's the right way to do it? Is it possible to ...

# arrow

[Emil Kantis]

If I want to fold with a curried suspend function, what's the right way to do it? Is it possible to inline it all the way?

[Emil Kantis]

This can't be used, for instance

fun curry(x: Int): suspend (Int) -> Unit = {
  suspendPrint(x + it)
}

[Emil Kantis]

image.png

[Youssef Shoaib [MOD]]

Just FYI it won't be inlined. I believe you can do { f(it) }

[Emil Kantis]

Thanks, yes that works but gets quite ugly when we need to do the currying at the callsite 😞

[Emil Kantis]

{ logAndNack(logger, message)(it) },

[Youssef Shoaib [MOD]]

That's why Kotlin isn't really intended to do currying. Returning a function type is rarely idiomatic in Kotlin. Instead, what you wanna do is just have logAndNack take all the needed arguments

[Emil Kantis]

Right, that's way more readable. 🙂 Thanks!

[Youssef Shoaib [MOD]]

If you want it to be nicer, then with context receivers (which are currently experimental, so not the best idea for production) you can turn the logger into a context receiver, so the call would just be logAndNack(message, it) which is even nicer.
In general, if you find yourself repeating a set of parameters pretty often, it's time to consider if they'd work as context receivers instead. This eliminates a good chunk of use-cases for currying.

[Emil Kantis]

we are using it, and have multiple receivers at this callsite even 😄

[Youssef Shoaib [MOD]]

Then yeah, experiment with turning logger into a context, and perhaps even message if it's repeated and makes sense

[Emil Kantis]

will consider adding the logger into the context 🙂

[simon.vergauwen]

That's why Kotlin isn't really intended to do currying.

100% this, although I've request several times to allow calling suspend lambdas where inline lambdas are allowed not sure if this ever made it into a YouTrack issue 🤔

[Emil Kantis]

If you end up creating an issue, feel free to link it so I can add a vote 😄