RE: Benefits of Sub-procedures

[Brian Parkins <PARKIB@xxxxxxxxxx>]

I get asked this question all the time by students on my ILE courses.

My take on this is that (static) procedure calls do _not_ replace (dynamic)
program calls - they _complement_ them.

The Dynamic Call (CALL and CALLP/EXTPGM) we've used since the S/38 is in
fact a WONDERFUL facility.  The late bind provides simplicity and
flexibility - with a relatively small performance overhead.  So, program
calls are A Good Thing - just as valuable as they ever have been.

On the other hand, Subprocedures provide a much better alternative to
Subroutines.  Many of the advantages have already been highlighted, (local
variables, parameter passing, automatic storage allocation + recursion,
more rigorous call interface, expression call, etc.).

To my mind, the big advantage of Subprocedures is the ability to "share"
code, (through a Service Program).

A Subroutine can be shared (proliferated) through the use of /COPY - but
results in a significant maintenance burden.  In contrast, a Subprocedure
can be packaged into Service Programs and shared in a similar manner to a
program object.  Service Programs act as a "function repository" - a means
of building and sharing your own built-in functions without the
proliferation problems of /COPY.

Now, if Subroutines (and /COPY) are _not_ used in an organisation, the
argument for the modularity/reuse which ILE supports becomes a little more
difficult.

Hope this helps.

Brian Parkins