Comment by uecker

13 hours ago

At the moment we can not call nested functions or other things from other language from C, which is a pretty big hole in our interoperability story. I do not see why we need to make any design decision to specify object layout, we simply need a code pointer and static chain pair, which would then be sufficient to call arbitrary entities from other languages.

2 comments

uecker

klodolph 7 hours ago

> I do not see why we need to make any design decision to specify object layout

> we simply need a code pointer and static chain pair

The code pointer and chain pair needs an object layout. You would have to pick a specific layout, and it would not be compatible with other languages that have a different layout.

Right now I can do this:

    struct a {
      void (*fun)(void *ctx);
      int data1;
      int data2;
    };
    struct b {
      void (*fun)(void *ctx);
      void *ctx;
    };

And I could call them:

     struct a *aptr;
     a->fun(aptr);

     struct b *bptr;
     b->fun(bptr->ctx);

There is only one neutral, maximally compatible option here—which is to have the function pointer separate from the arguments you want to pass in, and pass them in explicitly.

If you add closures to C you are making compatibility worse, not better.

uecker 4 hours ago

Except doing this manually does not allow me to directly call a C++ lambda, a Go closure, an Ada closure etc which I can not even express in C. So compatibility can not become worse, it is already maximally bad. And even where you can build a compatible solution in C, there are now different choices. Your examples already directly shows this contradicting your claim that here is only one option.
Adding such a type as a vocabulary type would fix all this. You can argue that we fix an object layout for a pointer pair, but this seems an acceptable trade-off to me. This seems far from your previous claim that this "requires design decisions that are equivalent to choosing a specific layout for objects in an object-oriented language." Note also that such a type can always adapt to different calling conventions of other languages by using the address of a static thunk as code pointer so it is very generic.