Hello,
Bill Wragg wrote:
Setll (VMAPVN) Zaptr;
Reade (VMAPVN) Zaptr;
(Vmapvn) is a field NOT a key list. Am on V5R3.
Coding the parenthesis is equivalent to coding the KLIST op-code. It
doesn't mean that VMAVPN is a keylist, it means that an unnamed/hidden
keylist is build, under the covers, and it contains VMAPVN as a key field.
All of the free format opcodes work exactly the same way they did in RPG
III, the syntax is just different. For example, the CHAIN op-code could
always accept either an RRN, a field, or a keylist (including a
keylist with only one KFLD) in it's factor1. The only difference in
free format is that the factor1 comes after the op-code, and you can use
parenthesis to create a temporary keylist on-the-fly.
For example, chaining with an RRN in fixed format (and RPG III) worked
like this:
FMYFILE IF E DISK
C RRN CHAIN MYFILE
To do the same thing in free format, simply move the RRN after the op-code:
chain RRN MYFILE;
You could also chain by a field if the file is keyed.
FMYFILE IF E K DISK
C FIELD CHAIN MYFILE
You do the same thing in free format, just put the factor1 after the
op-code:
chain FIELD MYFILE;
Free format offers the ability to declare keylists on the fly, and this
is a really simple and easy to use feature -- you just have to get it
into your head that PARENTHESIS=KLIST. Don't add parenthesis in a
situation where you wouldn't have used a keylist.
So traditional RPG had this:
FMYFILE IF E K DISK
C KEYLIST KLIST
C KFLD KEY1
C KFLD KEY2
C KEYLIST CHAIN MYFILE
And in free format, we can skip creating the KEYLIST field (it's only
useful for the CHAIN anyway) and have the system create a keylist on the
fly:
chain (KEY1:KEY2) MYFILE;
The one that seems to really confuse people is when you have only one
field in a KLIST. It's not any different from the previous example,
other than that there's only one field. PArenthesis is still equivalent
to KLIST:
FMYFILE IF E K DISK
C KEYLIST KLIST
C KFLD KEY1
C KEYLIST CHAIN MYFILE
And in free format:
chain (KEY1) MYFILE;
For some reason, this single key in a keylist thing seems to absolutely
baffle RPG programmers. They just can't seem to wrap their heads around
the idea that the parenthesis actually means KLIST.
When you access a file by RRN, you'd never, ever try to do the
following, would you?
FMYFILE IF E DISK
C KEYLIST KLIST
C KFLD RRN
C KEYLIST CHAIN MYFILE
That wouldn't work for RRN access, would it? You can't use a keylist
for an RRN -- everyone knows that. Nobody would even try to do the
above code.
That being the case, then why would you try the following code which is
the free format equivalent?
chain (RRN) MYFILE;
Because I put parenthesis, I've told it that I want a keylist (with only
one field in it.) If we know that the fixed format code with the KLIST
op-code won't work, *why* would we assume that the one with the
parenthesis *will* work? The only reason I can come up with is that
people don't really understand that parenthesis=klist. If you remember
that, it's actually very easy to understand.
midrange.com
