Re: First-class continuations in Kawa

[Per Bothner <per@bothner.com>]

On 8/8/21 7:29 AM, Arvydas Silanskas wrote:
> I merged and got the original code mostly working (leaving optimization refactoring for later),

Cool.

> var foo = (FooInterface) Class.forName("Foo").newInstance();
> foo.bar();
> ```
> 
> where FooInterface is an interface written in java, and Foo is a class created by `define-simple-class` on kawa side which specifies said interface as one of its supers.
> 
> * Am I using the recommended approach for java -> kawa interaction?

For the simple case. But clearly it might not work in general.

Does what you're trying to work when Foo is compiled with --full-tailcalls ?
The latter also makes use of a top-level handling loop, but there are automatic
"bridges" between the two styles of functions (see CallContext.runUntilDone).

Based on a trivial test, a bar method in a Foo class under --full-tailcall just becomes
a plain Java method (without tail-call support).

> * If yes to the first question, do we strongly care that this type of calling gets broken as a compromise? After all the (optionally enabled, by default disabled) full continuations will weaken interop anyway, so maybe this is not worth trying to save. I'm not certain what a fix would be, maybe some sort of custom equivalent to Class.forName, which would return a proxied class with the handling loop attached to the methods.

I think its ok to require people to write wrapper code in Scheme
when generating "simple" classes.

> * The points about using CPStyle / CALL_WITH_TAILCALLS from what I can understand are purely regarding optimizations, right? Or do you think that refactored code using those approaches would also solve the problem above?

Implementing CPStyle / CALL_WITH_CONTINUATIONS is mostly performance.
However, since CALL_WITH_CONTINUATIONS is sort of an extension of CALL_WITH_TAILCALLS,
I think the whole system would be better integrated.  Specifically having a single
CallContext.runUntilDone with that handles both continuations and tail-calls
would be preferable.   (I think I haven't looked much at this code in a while.)
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/