More ways to say 'program': why developers are exploiting C, Ada, Prolog and Lisp programming tools

Software Magazine, July, 1988 by Jerry Cashin

"Ada enforces structured design and implementation. Old-timers in the Fortran mode, for example, sometimes find it difficult to switch over to the new techniques. A good impetus for Ada in the defense environment is the Department of Defense Directive 3405.2, which dampened the trend toward seeking exemptions from its use," he said.

As with C, an important aspect of Ada is its acceptance as a formal standard. The language is trademarked by the Ada Joint Program Office (AJPO) within the DOD. Firms that produce a valid Ada compiler according to a vigorous set of testing procedures can use the Ada name in their product description.

NO ADA SUBSETS ALLOWED

No language subsets have been permitted to receive official sanctioning. Only the full complement of Ada constructs have been accepted by AJPO.

The Ada specification has been designated as both an Ansi and military standard. It is identified as Ansi/MILSTD 1815A (1983). Some of the subjects addressed in the documentation include:

* It defines the form of an Ada program unit, which is the basic entity in the language.

Each program unit in a procedure can be written, compiled, and debugged independent of other program units in the same procedures. The standard also directs how multiple program units come together to form one Ada program.

* The violations to the standard that must be detected, those that need not be detected, and the impact of executing an Ada program that contains standards deviations.

* Any permissible variations to the standard and the manner by which they will be documented are identified.

The standard does not address areas dealing with the conversion of an Ada program unit into executable code, the size of the executable module emanating from a source program, or the nature of error messages.

Basically, all implementation details are left to the compiler development process. This ensures that a modicum of innovation can be applied to individual compilers.

Some Ada users are dissatisfied with its performance in certain situations. They say it is inherently inappropriate for the very applications for which it is targeted, i.e. embedded systems, due to its cumbersome size. It has also lacked certain "necessities" such as interrupt handling and bit manipulation. Of course, whether the latter features are actually necessary depends on the application.

Despite this, DG's Doyle foresees a bright future for the language. "There will be more commercial use in the U.S. as evidenced by the formation of a commercial user group. Mission critical areas such as process control will lead the way in this arena," he asserts.

ADA DRAWBACK: FEW PROGRAMMERS

Perhaps the largest drawback in using Ada is a shortage of skilled programmers who can really use the language and its support environment in an effective manner. This situation is slowly being rectified, however, by universities and other training organizations that are increasing the emphasis to software engineering in general, and Ada in particular.