Symbolic Stream Generator (SSG) Resource Page

SSG is my favorite 1100/2200 programming environment. Executive Control Language (ECL) lacks a proc or macro facility. Instead, we have SSG, a small, powerful, procedurally-oriented language that does just what its name says--it allows you to generate symbolic streams (and optionally to @ADD them). In effect, it takes symbolic input and generates symbolic output based on a program called a skeleton. The language that the SSG processor implements is called Symstream.

Programming Tips and Techniques

Useful *COPY Procedures

The Future of SSG

Programming Tips and Techniques

I have seen a lot of bad SSG code. Here I present suggestions for writing good skeletons (as opposed to skeletons that merely work). I stress maintainability, ease of understanding, and code reuse.

Skeleton Design Guidelines

Use *DEFINE packets in long skeletons

Symstream Coding Guidelines

Stream Generation Statement (SGS) Design Guidelines

Use symbolic SGS references
Restrict your SGS labels to 32 characters (coming soon)
Avoid subfields except in special situations (coming soon)
Use an explicit null when a field is unknown or not applicable (coming soon)
Make your SGSs serve many skeletons (coming soon)
Think of your SGSs as third-normal form relations (coming soon)
Capture as much meaning as possible in your SGSs (coming soon)

Idioms and Tricks

Advanced Topics

Using @ZIP to create SGSs (coming soon)
Using MASM programs to create SGSs (coming soon)
How to write a processor in SSG ("the generic processor") (coming soon)
Using SSG to generate Web pages

Useful *COPY Procedures

The *COPY procs described here are ones I've found useful. Many of them help me follow the tips and techniques I recommend. Feel free to click on the proc name and save the proc to your hard disk.

CHECK-ERRCNT
This proc *ABORTs if system-defined global variable ERRCNT$ is set and it's a non-demand run. This is meant to be *COPY'd as the very last line of critical skeletons. By design, SSG does not perform ER ERR$ when it encounters certain syntax errors, even in batch mode. The SSG manual does not document which syntax errors cause ERR$ and which do not. Here's one that does not:
```
    *DISPLAY 'This message lacks a closing quote
```
In cases like this, a job with a syntactically incorrect skeleton (for which SSG will not @ADD any generated ECL) can FIN normally. Sometimes the syntax error won't be apparent because it'll be buried in a rarely-used path within the code. SSG does increment ERRCNT$, however, on any syntax error. Thus, *COPYing this proc at the end of important skeletons guarantees that syntactically incorrect skeletons never complete normally.

DAY-OF-WEEK
The Unisys-supplied DAY-OF-WEEK routine given in Appendix C of the SSG Programmer Reference Manual fails in the year 2000. See PLE # 16918521. I also wanted a more flexible routine that would accept input dates in either YYYYMMDD or YYMMDD format and would work irrespective of the setting of NEW_PROCESS$. So I wrote this version.

DEMAND-ONLY
This proc checks that the user is in demand. If not, it *ABORTs. This is useful if you wish to write skeletons that are to be used in demand only.

GET-EXT-DATE
Given an ISO 8601 date in internal format (YYYYMMDD), this proc returns the site-standard externally formatted date. This site-standard date format is specified by the SITE_DATE_FORMAT and SITE_DATE_SEP_CHAR SGSs. If these SGSs are not found, the date format defaults to ISO 8601 external format (YYYY-MM-DD). This proc allows you to format dates to each site's preference just be changing two SGSs.

GET-TS
If you need to generate a current timestamp, you may be tempted to use the built-in DATE$, and TIME$ SGSs. But SSG retrieves the date and time with differnent Executive Requests. If the clock just happens to cross midnight between ERs, you'll wind up with a timestamp that's off by 24 hours! This proc avoids that risk.

SET-DEST
Many skeletons need to direct *ACCEPT and *DISPLAY statements to the operator console in batch and to the terminal in demand. This proc sets a global variable, DEST, with the appropriate option for *ACCEPT and *DISPLAY. If you invoke this near the beginning of your skeleton, you can code '*ACCEPT,[*DEST]' or '*DISPLAY,[*DEST]' and thereby avoid the need for *IF logic.

SETUP-FIELDS
This proc creates global numeric variable for each RELATION SGS. This provides a symbolic field name so that skeleton writers can avoid coding numeric SGS field references.

The Future of SSG

In recent years Unisys has continued to enhance SSG, although new features tend to be minor ones. I believe that the dwindling 2200 customer base will not allow Unisys to fund much future development of SSG (and many other 2200 software products). But they recently implemented NFS #80469039 (allow SSG to accept console input), so perhaps I'm wrong.

Here is a list of what I think are the most needed new featues in SSG:

Improve the performance of *SORT. See closed UCF #19200027 for a good explanation of the problem.
Add the SSG release level to the built-in SOURCE$ SGS.
Provide an option to require that variables be explicitly declared before use. See rejected NFS #49634510.
Provide better control over variable scope. See rejected NFS #49634510.
Allow generated output to be up to 2047 characters (the SDF limit) rather than 132 characters (print file limit). See rejected NFS #49508917.

Revised 2010-02-12

Symbolic Stream Generator (SSG) Resource Page

Table of Contents

Programming Tips and Techniques

Useful *COPY Procedures

The Future of SSG