DOW & DOU

["Denis Robitaille" <DRobitaille@xxxxxxxxxxxx>]

I have seen a lot of discussion regarding the merit of dou and dow. I dont want 
to start that discussion again but i want to share with you someting i saw when 
i was in university. There i studied the LISP language. I do not recommand this 
 language but it had an original way to treat looping.

Basicaly, a loop process is made up of the folowing:

{Loop initialisation processing}
{loop begin}
{Before loop test processing}
{loop test}
{After loop test processing}
{loop end}

With this kind of construct, a DOW is when {Before loop test processing} is 
empty and DOU is when {After loop test processing} is empty. This gives us also 
the possibility to define loop where some processing is done before and after 
the test.

In RPG, it could look like this

C      CLEAR            x         {loop init}
C  Key SETLL   File                 "     "

C      DOL                       (new op code Do  Loop) {loop begin}

C      READ    File         55    {before loop test proc.}

C      DOTST    *in55 = *off     (new op code Loop test) {loop test}

C      EVAL    x = x + 1          {after loop test proc.}

C      ENDDO                      {loop end}

As you can see, this construct can replace both DOW and DOU. You can avoid the 
repetion of code (read before the loop and before the enddo in a dow).

I know that we will never see this on the AS/400 but I wanted to show that 
there is (in my mind) a better way.

Denis Robitaille
Cascades inc.
Tel: 819-363-5187
DRobitaille@cascades.com

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