Re: Suggested Technique -- RPG400-L

While I understand the idea of DO *hival coupled with a leave, why not just
say it in the first place, and have a DOU F3 and avoid the extra lines of
coding?  DOU F3 is pretty clear, too, isn't it? 
 
---------------------------------
Booth Martin
http://www.martinvt.com
---------------------------------
-------Original Message-------
 
From: RPG programming on the AS400 / iSeries
Date: 01/31/05 15:03:41
To: rpg400-l@xxxxxxxxxxxx
Subject: Re: Suggested Technique
 
Hi Alan,
 
<snip>
There are some brilliant programmers here, however, who advocate avoiding
use of the "iter" and "leave" op-codes. I find it hard to avoid using them
myself, but am still open on that issue.
</snip>
 
Now there's a statement! :-)
 
I would be VERY interested to hear the reasons why LEAVE and ITER have
entered the "Hall of Shame" along with CABxx and GOTO.
 
Personally, I find them very useful and would need a very, very hard sell to
convince me to stop using them. They do not preclude well structured code,
they have definite branching end-points, and they do not make code less
readable to a developer: All long-standing accusations levelled at CABxx and
GOTO.
 
For example - a classic screen loop:
 
// Display screen...
do *hival
 
exfmt screen
 
// If user presses F3, leave screen loop...
if F3_pressed
leave
endif
 
// Validate user input...
validateInput()
 
// If user enters invalid data, re-display screen, displaying error
message...
if userEntersInvalidData
iter
endif
 
// If user elects to update current valid data, update and leave screen...
if F8_update
updateData()
leave
endif
 
enddo
 
 
For me this code is simple - you can only leave the screen if you press F3
or update valid data. How do I know??? There's only two ways to leave the
screen - via the two LEAVE op-codes. If the code goes beyond the enddo then
F3 or F8 MUST have been pressed. In the case of F8, valid data MUST have
been entered. If the user enters invalid data then I force a re-display of
the screen (ITER) before any update code is reached - this forms a nice code
buffer, beyond which I am assured that the input data is valid.
 
I also prefer using "do *hival" because I do not want any "implicit" exits
of the loop. I want to see the exit strategy EXPLICITLY coded within the
screen loop. My time is more precious than the CPU cycle time. If I can
read/modify the code faster because there are large marker flags in front of
me then my company saves money. It's the old adage - KISS!
 
Just my preference.
 
Cheers
 
Larry Ducie
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