Re: No syntax checking in free-form RPG

On the other hand Verify is a nice addition. A pleasant piece of progress,
and a fair trade up for the loss of syntax checking. 
 
 
 
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Booth Martin http://www.MartinVT.com
Booth@xxxxxxxxxxxx
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-------Original Message-------
 
From: RPG programming on the AS400 / iSeries
Date: Monday, July 28, 2003 7:48:38 AM
To: rpg400-l@xxxxxxxxxxxx
Subject: Re: No syntax checking in free-form RPG
 
Jon Paris wrote:
> >> The explanation given is that free-form is too hard to parse.
>
> Where did you get this "explanation" Joe? The fact that the syntax checker
> wasn't working was quite a surprise to me - perhaps because I tend to
verify
> so frequently I just hadn't noticed. It strikes me as a (hopefully)
> temporary aberration caused by a resource shortage. Much like the horrible
> state of the V5R2 RPG documentation in CODE (haven't checked in jLPEX)
which
> omits a whole bunch of stuff like %KDS and has a number of simple errors
> like the bits on using a DS as a result field.
 
Jon: Where did Joe get that? Probably from one of my postings on
MCPressOnline. The URL is:
 
http://www.mcpressonline.com/mc?128%40%40.6ae739e2%21SearchMark=1%231
 
(MCPressOnline's URL's are a bit of a pain since they don't properly
encode the query string. urllib.quote() comes in handy in
situations like this.)
 
For those without web access, I'll repeat my answer here:
 
=================================================================
Syntax checking of free-form RPG?
 
Short answer: It doesn't.
 
Why not? The problem is that if the syntax checker were asked to
check a line in a free-form calc, it would have to scan backwards
through the source to find the beginning of the statement. Because
of the continuation rules for free-form statements, the rules for
end-of-line comments, and the rules for continuing literals, the
only way to properly find the beginning of the statement would be to
scan back all the way to the beginning of the /FREE block and then
scan forwards. The delay in this operation might well be quite
noticable if the current /FREE block was big.
 
On the other hand, since you don't have to worry about coding things
in particular columns, and since there's not much syntax checking
for expressions anyways, syntax checking for free-form statements
probably wouldn't give you much benefit anyways, even if we could
come up with a way to quickly identify the beginning of the statement.
 
Cheers! Hans
=================================================================
 
To summarize:
 
1) Doing a fast syntax check of a free-form statement may well be
impossible because of the syntax rules of the language. The delay in
checking would steadily increase as the size of your /free block grows.
 
The problem is to try to locate the beginning of a statement from
some arbitrary point in the source. Think about scanning backwards
to locate the previous semi-colon. If you find a semi-colon, how can
you tell that it's not within a comment or a character literal? Or,
if you find an apostrophe, how can you tell if it begins or ends a
literal? If you could come up with some algorithm, would it work for
syntactically invalid source as well as valid source? (There's no
point is syntax checking if you know your source is good already!)
 
2) Syntax checking would provide less benefit for free-form calcs
than for fixed-form calcs anyways simply because the syntax rules
are less restrictive.
 
3) As I'm sure you already know, in development, more emphasis is
being placed on improving the workstation based tools.
 
Cheers! Hans