From: tec@netcom.com (Tim Cargile)
Message-Id: <tecC7q3q0.Aw3@netcom.com>
Subject: Re: #defines in 4gl
Date: Fri, 28 May 1993 06:08:24 GMT
Reply-To: tec@netcom.com (Tim Cargile)
Organization: NETCOM On-line Communication Services (408 241-9760 guest)
X-Informix-List-Id: <news.3477>

In article <1ttg96INNiat@emory.mathcs.emory.edu> archer!ciesla@stairs.att.com writes:
} For years, I've wished 4GL had a feature that would allow the
} use of #define, #ifdef, #else, #include, . . .
} 
} Has anyone figured out a way to do this in spite of Informix?  And you folks
} at Informix:  Why has this feature never been supported in the language?
}

I started pre-processing Informix languages in 1986 while installing
a modification to a 200 line "calc" section into 40 ACE reports
(I didn't desire to convert it to a C function for some reason?).
I went on to pre-process sperform and thought (still do) seriously about
applying pp to SQL scripts.

The pre-processor of choice was "cpp" because of my familiarity with C
and its capabilities (include directories, etc).  Pre-processing was
implemented via shell scripts and placed into makefile "rules" sections.
The scripts had names like "ppcace" (pre-process and compile ace).

When 4GL arrived, I wrote a 4GL pp script (cpp-based), but hesitated
to introduce pp'd 4GL with the client (at the time) because of fears that
it would be judged as heretical by employees.   I mothballed it.

Later, it was used successfully for a major project by that client when
I disclosed it.  The project leaders were C programmers, of course.

I've seen the intent to use "m4" once by a major software developer once
and tried it myself ONCE.  I personally found m4's syntax so alien and its
capabilities so limited in "header inclusion" it was dropped.
In Relational Application Group's (RAG) Informix development environment
model, header files are BASE directory referenced and I recall having to
apply some tricks with M4 in order to avoid hard-coding full-paths into
"include" statements.

    The trick I believe in using pp'd 4GL is to use it judiciously.

This subject is highly-religious, but I can tell you that there was nearly
a mutiny by the 4GL developers on the above project when people started
nesting "includes" too deep.  I saw several program "mains" on the project
with "ifdefs" nested 15 deep in order to get (probably over-maximized)
source code sharing.  I also saw a > 2000 line "include" file containing
dozens of "ifdefs" to get re-usable (shared) "after/before" field logic.
It was "slightly" unreadable - which is worse that "totally" unreadable
... one keeps trying.

Along with providing reasonable source code reusablity, centralization,
etc. and all the other GOOD things, I find pre-processing very useful for
providing literal constant declaration for enhanced documentation.

One can also do cute things like (if one has the nerve/power):

#include "i4gldefs.4gh"
#include "msgdefs.4gh"

#define BOOLEAN integer  (this would actually be in i4gldefs, of course)

main
        define l_is_it_or_not BOOLEAN

        if g_what is TRUE then
			let l_is_it_or_not = TRUE
		end if
end main

----------------------------------------------------------------------------
Anyway, I'm including a ppcc4gl script that has seen actual, recent service
(but under makefile rules - rarely from the command line and not very often
from the r4gl menu system, either.)

It supports DEBUG and XACTION environment variables for conditional
debug/transaction compilation.  The "cc -E" invocation to get "cpp" might
have to be adjusted according to platform.  Also, the pre-processed files
are retained for RDS debugger availability and error correction.
There is a similar script for RDS - "pprc4gl".



    - Good Luck

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   | Tim Cargile                   | INTERNET: tec@netcom4.netcom.com |
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   What this country needs is a good 5 cent Informix Survival Kit