[Info-vax] BASIC and AST routines

[Simon Clubley]

On 2021-11-24, Arne Vajhøj <arne at vajhoej.dk> wrote:
> On 11/24/2021 8:46 AM, Simon Clubley wrote:
>> On 2021-11-23, Arne Vajhøj <arne at vajhoej.dk> wrote:
>>>
>>> 2) Why are those arguments there?
>>>
>>> It is not obvious to me why Macro-32 code would want to use them
>>> any more than C or Basic code.
>>>
>> 
>> Nor to me. In an OS with the proper levels of abstraction, those
>> hardware-specific registers simply should not be needed (or even
>> visible) to a function used as the target of what is essentially
>> just another way of doing an asynchronous callback to a function
>> within an application.
>
> So why did you suggest that it was for Macro-32?
>

I suggested it was needed because clearly something needs to be manually
preserved by the programmer in Macro-32 code that simply would not be
an issue if VMS was based around an higher-level language instead.

>> Since they are visible, and since they are of no use to a normal
>> compiled language, there must be some cases where you have to
>> preserve these values manually in Macro-32, whereas a OS based
>> around a higher-level language would have its compilers generate
>> the correct code sequences for you without you having to worry
>> about any of this at all.
>
> So it is there for Macro-32 because VMS C could have had a feature
> but actually does not that does something that nobody seems to be doing?
>

No, it's there because the lowest supported application language on
VMS is Macro-32 instead of C or another language and hence that had
to be factored into the VMS API design.

> And are there really any difference between the non-existing C:
>
> int __damn_ast foobar()
>
> and the non-existing Macro-32:
>
> .entry  foobar
> .damn_ast
>

Yes. Code generation in a compiled language is totally abstracted
away from the source code the compiler is working with.

In Macro-32, the assembler is translating the source code, not
rewriting it, and hence there are only a small number of transformations
it can do on the source code.

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
Walking destinations on a map are further away than they appear.