Is there any way to combine two functions to make ...

# announcements

[Rob Murdock]

Is there any way to combine two functions to make a third function such as this?

val function1: (Int, String, Byte) -> String = { i: Int, s: String, byte: Byte -> "example" }

val function2: (String) -> Int = { -1 }

//to get something like 
val function3: (Int, String, Byte) -> Int = function1.then(function2)

obviously the “then” function is fictional otherwise i wouldn’t ask. I’d love to be able to do this without actually having to know function1's arguments explicitly… just that it returns a type that matches the arguments of function2

[Ray Eldath]

infix fun <A, B, C, D, E>((A, B, C) -> D).compose(after: (D) -> E) = after(this()) ?

purely hand-written, no guarantee compileable.

[Ray Eldath]

and i think arrow may have the hole composition of these signatures, for different functions.
https://arrow-kt.io

[Rob Murdock]

yeah I figured it’d be something arrow would want. I’m trying to stay multiplatform compatible and last i checked arrow isn’t there yet 🤔

Good lead, thanks

[Robert Jaros]

infix fun <A, B, C, D, E>((A, B, C) -> D).compose(after: (D) -> E) = { a: A, b: B, c: C -> after(this(a,b,c)) }

this is compiling and working

[Robert Jaros]

https://pl.kotl.in/Bn4i6RwUc

[Rob Murdock]

so I’ll have to have versions of that function for every number of parameters eh

[Rob Murdock]

the secret sauce I want is to be able to convert a data class constructor function to a function that returns something else, and capitalize on the autogenerated data class stuff

[Robert Jaros]

That's what Arrow is doing for you 😉
https://github.com/arrow-kt/arrow/blob/master/modules/core/arrow-syntax/src/main/kotlin/arrow/syntax/function/complement.kt

[Rob Murdock]

wtb multiplatform arrow! 🙂