lambdaN() in typescript

[dakom]

Is it possible to provide more details on where one must use the lambdaN() functions?

Nothing in the examples/ folder uses it as far as I can tell, yet closures are a big part of JS/TS in general and one might think they need to use lambdaN() everywhere, since the Readme says:

You must declare any Sodium objects held inside closures using wrapper functions lambda1, [...]

The API docs speak of it in terms of sample...

There is something in the test suite, but it's not entirely clear to me why it's necessary in the map_track test since t isn't actually used in the lambda. Lower down, in switchC, at a glance it makes more sense to me since ca and cb are only referenced in that lambda and not used elsewhere... but I'm still not 100% clear on where I need to use lambdaN() and where I don't.

[the-real-blackh]

Hi David,

You need it when your closure references a Sodium object. Here's a test case where it's used

const csw = csw_str.map(lambda1(s => s == "ca" ? ca : cb, [ca, cb]))

You are informing Sodium that the map operation has a dependency on the ca and cb objects, because it has no other way of knowing. In practice, lambdaN will only ever be needed when you are using Cell.switchC() or Cell.switchS().

Steve

[the-real-blackh]

Hi David,

This line in your code from Switch best practices needs a lambda1 declaration!

let choices: Stream<Cell<ChannelInfo>> = remote.map(n => channels[n]);

should be

let choices: Stream<Cell<ChannelInfo>> = remote.map(lambda1(n => channels[n], channels));

(I added a comment to that thread too.)

Steve

[dakom]

Thanks for the explanation, and it helps to see it in my own code

However, this is still a bit confusing for me because the channels are given listeners here:

channels.forEach(c => c.listen(() => { }));

Is that not enough for sodium to track the dependencies?

Alternatively, would there be a way for sodium to give runtime warnings/errors if lambda wasn't used where it needed to be?

[the-real-blackh]

Hi David,

Registering a listener on each cell that is used inside a closure will (probably) result in working code, but it makes one bit of the code dependent on another bit of the code. And, memory management won't be automatic. If you just follow the rule, which is that any Sodium objects used inside a closure must be declared using lambda1(), then everything is guaranteed to works and have correct memory management.

I have done some work to give warnings/errors if the lambda isn't used where it's needed to be - an exception saying send() shouldn't be called when there are no listeners. Some work would be needed to get this to be correct in all cases. I have not thought through whether this is possible or not.

Steve

[dakom]

Warnings in all cases would be immensely helpful if it doesn't drain performance