[Info-vax] Access to _all_ VMS system services and library functions from DCL ?

[David Froble]

Simon Clubley wrote:
> On 2017-07-12, David Froble <davef at tsoft-inc.com> wrote:
>> Simon Clubley wrote:
>>> On 2017-07-11, David Froble <davef at tsoft-inc.com> wrote:
>>>> Simon Clubley wrote:
>>>>> A single block of data which is directly accessed is too limiting and
>>>>> will cause massive maintainence problems as structures are changed and
>>>>> field sizes changed in the future.
>>>> Why?
>>>>
>>> Because existing binaries will now be looking at the wrong locations
>>> for the data items they need.
>> Not if the system service rejects an improper data block.
>>
> 
> Erm, in your scheme, it's the _output_ from the system service which
> will have changed format, not the input.
> 
>>>>> This will lead to a different version of the data block for every
>>>>> change in the future and all these versions would have to be kept
>>>>> around in the future as well as the code to populate them.
>>>> Why?
>>>>
>>> Because it is expected that you are able to run existing user mode
>>> applications unchanged on the upcoming versions of an operating system.
>> Only if you worship at the 100% compatibility alter.  Which as Steve has 
>> mentioned, stifles new capabilities.  Face it, if you want to be able to 
>> improve, then sometimes there is a price to be paid.  If you don't want 
>> improvements, run your current version of the OS forever.
> 
> This scheme instead would be pretty close to 0% upwards compatibility.

Not true at all.  All the code you've written, with the exception of usage of 
"changed" system services, will still run.  No re-build required.

The alternative would be to stiffle improvements.  Which would you choose?

> Your scheme would break compatibility on every minor change to the
> data structure, not just the major changes.
> 
> $ set response/mode=good_natured
> 
> Since I refuse to believe you can't see that, I am going to assume
> instead that you are just trolling for responses. :-)

No, not at all.  What part of an application calls system service routines?  I'd 
suggest rarely.  Now, if something rarely used needs to break compatibility, 
that would have little effect on an application.