I'm playing with functions. Here, the restriction...

# arrow

[julian]

I'm playing with functions.

Here, the restriction I've set for myself is that f2 depends on f1 and f1 depends on E, but E must be supplied late, after the program has already been constructed.

All that's fine, as far as it goes.

I'm particularly interested in the function f3 . It seems like there might be a named pattern for what it's doing. It kind of behaves like partially, except it defers the partial application till later. Then it partially applies to f2 the result of executing the deferred function (when that happens).

If such a pattern exists, what's its name? Do helper functions already exist in Arrow to do this for me? Basically, is there a better way?

Thanks much!

Untitled

[raulraja]

Looks like a version of function currying https://github.com/arrow-kt/arrow-core/blob/60c85c673e523e45b5b196458ef51abc5c3b6780/arrow-core-data/src/main/kotlin/arrow/core/predef.kt#L5

[julian]

@raulraja Kind of. But with the curry function in core one has to respect the order of the parameters of the function being curried.

[julian]

I also got a similar result this way:

val r1 = Reader { e: E -> Id(f1(p3 = e)) }
val r2 = r1.map { f -> Reader { a: A -> Id(f(p1 = a)) } }
val d = r2.runId(E()).runId(A())(F())

I don't know what I'm doing. 🤣 I'm just kinda pounding at the keyboard and seeing what happens.

[raulraja]

This is very similar to a technique in scala called PartiallyApplied which is used to only have to provide one type arg instead of two in functions that take two. You create a class that partially applies the first arg then the second

[julian]

@raulraja Yeah, that sounds right.

[raulraja]

Reader and Id are still there for the novelty but they are kind of pointless in Kotlin since the same can be expressed in direct style with the same semantics:

fun E.r1() = f1(...)
fun A.r2() = r1(...)
fun d() = E().r2(...

[julian]

That's really interesting! I'm going to try translating what I have to ^.