[raluk]

One thing that most languages are lacking is expressing lazy return values. -> await f1() + await f2() and to express this concurently requres manually handing of futures.

[jayd16]

you mean like?

   await Join(f1(), f2())

Although more realistically

   Promise1 = f1(); Promise2 = f2();
   await Join(Promise1, Promise2);

But also, futures are the expression of lazy values so I'm not sure what else you'd be asking for.

[raluk]

This is what i hand in mind whit "manually handing of futures". In this case you have to write

   Promise1 = f1(); Promise2 = f2();
   v1,v2 = await Join(Promise1, Promise2);
   return v1 + v2

I think this is just too much of synthactic noise.

On the other hand, it is necessary becase some of underlying async calls can be order dependend.

for example

    await sock.rec(1) == 'A' && await sock.rec(1) == 'B'

checks that first received socket byte is A and second is B. This is clearly order dependant that can't be executed concurrently out of order.

[jayd16]

I suppose you'd have to make

    SumAsync(F1(),f2());

Buy it's kind of intractable, isn't it? Your language has to assume order dependency or independency and specify the other. Most seem to stick with lexical ordering implies execution order.

I think some use curly brace scoping to break up dependency. I want to say kotlin does something like this.

This is why they say async is a viral pattern but IMO that's because you're adding specificity and function coloring is necessary and good.

[sedatk]

Which languages do have such a thing?

[steveklabnik]

Rust does this, if you don’t call await on them. You can then await on the join of both.

[sedatk]

Is the "join" syntax part of the language?

[deathanatos]

Why is having it be syntax necessary or beneficial?

One might say "Rust's existing feature set makes this possible already, why dedicate syntax where none is needed?"

(…and I think that's a reasonably pragmatic stance, too. Joins/selects are somewhat infrequent, the impediments that writing out a join puts on the program relatively light… what problem would be solved?

vs. `?`, which sugars a common thing that non-dedicated syntax can represent (a try! macro is sufficient to replace ?) but for which the burden on the coder is much higher, in terms of code readability & writability.)

[tcfhgj]

no

https://doc.rust-lang.org/std/future/macro.join.html

[sedatk]

Then it doesn’t apply in this case.

[tcfhgj]

why?

[Twey]

I suppose Haskell does, as `(+) <$> f1 <*> f2`.

[raluk]

In there is also ApplicativeDo that works nicely with this.

    do 
      x <- f1
      y <- f2
      return $ x + y

this is evaluated as applicative in same way.

[zmj]

That's because f2's result could depend on whether f1 has executed.