World: r3wp

That would be just a little code, and it's obvious that you have 
to develop your programs to stay in sync with a language that's in 
alpha status

Yup. But it's also good to warn them of planned developments once 
they're definitely planned, and this one is pretty well established.

Exactly, so that's the reason to start using the handle! type now

No, that's a good reason to *add the handle! type to Red/System* 
now, as a preemptively reserved word. Not a reason to use the word 
handle! to refer to a completely different thing.

It still means that I start writing "handle!" in my code now

Perhaps it could be a name for a non-dereferenceable void pointer 
type, since that's the closest C equivalent.

Basically, Red's handle! type would be the same as R3's handle! type. 
Opaque value that is pointer sized, but can't be used as a pointer 
without typecasting, and no arithmetic possible. No conversions to 
other datatypes either in typesafe code.

That's in Red. Red/System is a different context

Yes, but Red/System's main purpose is to do things with Red data, 
so it needs to have access to Red's types, even if its own literal 
types are different. So Red/System needs to have a handle! type, 
even though Red/System code would need to typecast values of that 
type to something else in order to be able to do anything with them.

I don't see why it couldn't be the same type

Alias types are user-defined. The handle! type would be system-intrinsic.

Yes, a temporary difference in declaration, because as of now, there 
is no handle! type to declare

As long as the type is defined in the core runtime code, rather than 
in user code, there is no difference.

Exactly

And since it isn't defined in the runtime now, I have to write it 
myself until that time

The main thing is that it needs to be defined as *non-dereferenceable* 
and *no pointer arithmetic allowed*, so if Red/System's equivalent 
of the void pointer is so restricted, that will do. If dereferencing 
or pointer arithmetic is allowed on Red/System's void pointer type, 
that needs to be fixed asap.

Why? That would be the behaviour in Red. Red/System's task is to 
actually be able to do something with a pointer

Unless you want to make Red a true capabllities language, but you 
are opposed to that concept

In a strongly typed language, which even Red/System is, dereferencing 
a pointer means getting a value back that is of a known type; pointer 
arithmetic means adding in increments of the size of that type. A 
void pointer references nothing, and that nothing has no size. You 
must be required to typecast to another pointer type explicitly if 
you want to dereference the pointer, or to know how much to increment 
or decrement it.

The difference between Red and Red/System is that such typecasts 
are possible in Red/System.

If Red/System truely is to be strongly typed, there needs to be more 
than just pointer! [integer!]. The issue I'm currently having is 
exactly that there is no matching declaration for what I need

Right, there need to be pointers to other types. And support for 
more types, for that matter.

I'm not under a strong impression that this is planned. So currently, 
I need to treat Red/System as weakly typed

It is not currently planned *by Doc* to have Red/System be a complete 
language, since he only needs it to access a few system libraries 
and implement the Red runtime. He's said that others are welcome 
to contribute the necessary changes to make Red/System a more complete 
language.

If you want to use Red/System as-is to do more advanced stuff than 
that, then go ahead and break the rules. Or better yet, add the features 
you're missing.

I understand the burdens of future programs, but I've written a program 
right now that I have to keep working

In other words, the rules you're talking about don't exist

Still, I would welcome Red/System becoming strictly strongly typed

If and when that happens, I'll update my programs to be compliant, 
as I'm doing now

Well, it can't become strictly strongly typed, as a certain amount 
of type breakage is the whole point of its existence. You can't be 
strictly strongly typed if you have typecasting, pointer arithmetic, 
literal pointer values, or the ability to call C code. Red/System 
is supposed to be strongly typed with those rule breakers, in order 
to shield Red itself from those features.

Ehm, yes, that's what I've been saying all the time

Doc, defining handle! with alias doesn't work:

*** Compilation Error: invalid struct syntax: [handle!]

*** in: %/users/administrator/Red/Red-ZeroMQ-binding/examples/../ZeroMQ-binding.reds 
*** at:  [struct [
        content [handle!]

#define doesn't work, either:

** Script Error: Cannot use path on none! value
** Where: check-arguments-type
** Near: if all [
    not empty? spec: entry/2/4 
    block? spec/1
] [
    spec: next spec
] 
foreach

You wanted to know if the appointed error locations are correct. 
That seems to be alright, and the error for a struct is nicely descriptive, 
but an error for a function definition is rather unspecific:

*** Compilation Error: invalid definition for function send: [
    socket [pointer!] 
    data [pointer!] 
    size [integer!] 
    flags [integer!] 
    return: [logic!]
]

*** in: %/users/administrator/Red/Red-ZeroMQ-binding/examples/../ZeroMQ-binding.reds 
*** at:  [func [
        socket [pointer!]

Oh wait. I have to use a block for #define, and then it works. But 
not ALIAS

And the error output for a function starts at the offending parameter, 
so that's actually pretty good, but it's not obvious

Here's a message that's not very clear:

*** Compilation Error: type mismatch 
*** expected: [pointer!] , found: [integer!]

*** in: %/users/administrator/Red/Red-ZeroMQ-binding/examples/../ZeroMQ-binding.reds 
*** at:  [0 as-message message data]

I can't compare pointers to zero any more. Presumably, these are 
the arguments to the zero? function, but that information is lost

As a nitpick, there's an excess space in the message, before the 
comma

It seems that NULL is defined as integer! 0

So it seems that there is no way anymore to pass a null pointer to 
a function or to compare a pointer to null

null-p: as [pointer! [integer!]] 0

does that work?

I tried AS POINTER!

The only syntax I can get to compile is as pointer! [integer!] 0

null-ptr: pointer [integer!]
null-ptr/value: 0

should probably work as well