Re: 'ILE RPG' or 'RPG IV' . What's the difference!!!

You can use the old call mechanism and for things that are not calling each
other more than a few times it probably makes the most sense to do this.

However look at procedures this way.
A problem is best solved by breaking it up into sub problems and then
examining each sub problem and breaking it down etc... This is called
functional decomposition. What is the benefit to this? Well by breaking a
problem into smaller chunks it is much easier to test in all possible ways.
Once you have a given chunk of code that works (even handling rotten
input/output) you should not have to examine this code again. The only thing
that is important then is the interface to the function, it's name and
purpose. The internal workings should be a black box (you should not need to
know how it does it's work only that it does).

Sub procedures are the only way you can have local variables in RPG. Local
variables are invisible to the rest of the program at large and therefore
can not be violated by any normal means ( the AS/400 makes it even harder to
trash local variables than most other systems and even on other systems it
is usually not a trivial matter to figure out how to corrupt locals).

IMHO
Sub procedures should do ONE thing and do it VERY WELL.
They should have a well defined interface, that meaning they rely totally on
their parameters and not on Global variables or their uglier cousins *IMPORT
variables. (At least most of the time :-)
They should be well documented in the /COPY member.
Ideally they should be available in both Service Program (Generally
preferred) and Module form.

So if you have a batch program that needs to perform a certain function for
each record you surely do not want to do an external call for this due to
the overhead. The only solution prior to ILE RPG was to copy the code to do
that work into your program and then you have multiple versions of the same
code spread all over the place... Very bad!!! For example how many ways have
you seen in home brew and vendor apps of working with dates??? How many
times have you seen the same code or similar code copied over and over in a
multitude of programs?

How many times have you accidentally changed a variable that "shouldn't have
mattered" and found out that the earth came to a screeching halt? Sub
procedures and their local variables can help to dramatically reduce this
problem!!!

Oh and for everyone who is reading this if you can find a good academic
definition of Structured Programming Methodology I would love to have a
source other than my own memory to quote from... For some reason people do
not think I am the be all, end all as far as answers go :-)

I hope this helps
Eric

______________________________________________
Eric N. Wilson
President
Doulos Software & Computer Services
2913 N Alder St.
Tacoma WA 98407


----- Original Message -----
From: <rbrightman@amclog.com>
To: <RPG400-L@midrange.com>
Sent: Friday, April 07, 2000 11:37 AM
Subject: Re: 'ILE RPG' or 'RPG IV' . What's the difference!!!


>
>
> If its true that ILE was meant to reuse specific code in multiple
programs, then
> is reminds me of why IBM gave us printer files (prtf). These were intended
to be
> used in multiple programs also. But I have never used the same printer
file in
> two or more programs because each program requires a different report.
Only a
> few routines would need to be modularized usually. So whats the benefit of
ILE?
> Why can't we still use the old 'call' ?
>
>
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