Re: Is RPG dying

On 2/21/2012 9:54 AM, john e wrote:

For example, the main part of a (RPG) program handles user input, such as
command keys.
You could see these as "events" which cause a specific subroutine to
execute. If the main part simple checks to see what command key is pressed
and then simply calls a subroutine to handle it you already have an
event-driven program. You just have to see it that way.

So you could say that RPG was event-driven all along because there are some
pre-defined events (such as total-time happening) which exectutes some code
associated with it. But event-driven means that those "events" can happen
any time, in no specific order. Some events may happen never, and others
1000 times repeated. There is no pre-defined structure. And the RPG cycle
sure has a predefined structure in which these "events" happen in a well
defined order (and only once etc).

The idea of events is to decouple "the event" and "the code". This could be
applies in all sorts of situations.

You could say that RPG was state of the art in 1959 because it was (the
first?) "4GL" (declarative) language with which you specify on a high-level
what report to produce.

IBM has always led the way in language and operating system support. ILE RPG is as event driven as they come; persistent service programs provide everything you could need for a powerful event-driven back end. Note the emphasis: back end. The IBM midrange platform has never been about the GUI; they focused what were originally very limited CPU cycles on getting data in and out of the database. Even the green screen was a powerful client/sever architecture; the processing power in a 5250 terminal was comparable to a lot of other computers in its day.

Anyway, I've been designing and implementing a completely event-driven system using a service program as the "backing bean" and everything else being done in Rich UI using Dojo widgets to do JSON calls to Java web services on the host. The application has a large, multi-pane UI in which changes at one part of the UI flow through to the rest as soon as the user exits a field. It's fast, it's powerful, and I write all my business logic in RPG (well, except when it's simpler to just do it in SQL in the service).

Of course, I'm doing all of this through EGL so I don't have to do all that tedious plumbing, but the concept is there. ILE RPG and ILE in general is VERY well suited for event-driven programming; you just have to know how to design it.

Joe