RE: FOR op-code

["Bob Cozzi \(RPGIV\)" <cozzi@xxxxxxxxx>]

Hans,

The DO operation is NOT upwardly compatible, is it?
I mean, if you say:

C        10      DO          1       Count
C..........
C                EndDO       -1

The loop does not work as expected. You can't count down from 10 to 1.
But the code does compile. So how do this port to FOR?
I don't see how upward compatibility for the DO operation should have
influenced the FOR? FYI, I too was surprised that "FOR X=10 downto 1 by
-1" did not work. So I solve my personal issue, by leaving off the "BY"
clause.
At least you didn't use colons to separate the values! Thank you!


Bob Cozzi
cozzi@rpgiv.com
Visit the new on-line iSeries Forums at: http://www.rpgiv.com/forum

> -----Original Message-----
> From: rpg400-l-admin@midrange.com [mailto:rpg400-l-admin@midrange.com]
On
> Behalf Of boldt@ca.ibm.com
> Sent: Wednesday, December 12, 2001 10:06 AM
> To: rpg400-l@midrange.com
> Subject: Re: FOR op-code
>
> Tom wrote:
> >I take your point about breaking existing FOR loops.  That would be
bad.
> >But as far as the syntax making it clear which direction to
iterate....
> The
> >problem is that I must know *beforehand* which direction to loop and
> commit
> >that to code.  Maybe it's that (reaching way back) BASIC showing.
The
> >increment variable should be evaluated once at the beginning of the
loop.
>
> Well, there are lot's of different ways to design a FOR loop.
> Why did we do it that way?  I believe we wanted to provide an
> upward compatible way to convert old-style iterative DO loops
> to an expression-style syntax.  With DO loops, you can change
> increment and limit values on the fly. You're right, probably
> the better design would have the limit and increment computed
> once at the beginning of the loop.
>
> (Actually, FOR is almost completely upward compatible with the
> DO opcode.  One remaining incompatibility should be eliminated
> in the next release of the compiler.)
>
> >An application for this that springs to mind is a READ/READP loop
where I
> >need to get, let's say, the next 10 records or the previous 10
records.
> Say
> >for a page-at-a-time SFL or something similar.
>
> Well, since you have distinct READ and READP operations, you
> still have to know the direction of the loop beforehand
> anyways, right?
>
> Cheers!  Hans
>
> Hans Boldt, ILE RPG Development, IBM Toronto Lab, boldt@ca.ibm.com
>
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