In optics, is there a way to "tap" on foci? I want...

# arrow

[Luke]

In optics, is there a way to "tap" on foci? I want to log stuff for debugging purposes. I'm searching for something like:

MyClass.a.b.c.tap { println(it) }.d.e.f.set(state, newValue)

[simon.vergauwen]

Hey @Luke,

Something like that is not possible,
you could however split this up a bit.

val pathC = MyClass.a.b.c
val pathF = pathC.d.e.f

pathC.get(state).also(::println)
pathF.set(state, newValue)

[pakoito]

puts on golf cap

MyClass.a.b.c.also { println(get(state)) }.d.e.f.set(state, newValue)

[Luke]

That would work nicely thank you @pakoito. I didn't think of that.

@simon.vergauwen, I'm curious about why it would be impossible though... Do you mean it's impossible right now because there is no function implemented in the library for it? Because I wrote this that seems to work fine:

inline fun <T, U> Every<T, U>.tap(crossinline block: (U) -> Unit): Every<T, U> = plus(
    Iso(
        get = { it.also(block) },
        reverseGet = ::identity
    )
)

But for my debugging, yes, it's overkill