Re: Papers saying Ada as an overly complex language and hard to implement

[Markus Kuhn <Markus.Kuhn@cl.cam.ac.uk>]

Yongxiang Gao wrote:
> Actually, Ada is described as a complex language in a lot of places. However, most
> of them just address one or two words, so that they are worthless for me.

The notion that Ada is a "too complex" language is -- although
unfortunately still widely believed among people who never
used the language -- based on a few historic misconceptions:

- Ada was the first modern language for which a formal ANSI/ISO
  standard (the reference model) was widely published before
  good tutorials and free compilers where available. We now know
  that reading a language reference manual is a very bad way of
  getting a first impression of a language (just try to learn
  Java or C++ from the RM!). But in the early days, people
  compared the readability of the very formally written Ada83
  specification with the very informally written and incomplete
  tutorials by Wirth and K&R about their languages (Pascal and
  C). Of course Ada seemed to be much more complex. Once you
  have read both the Ada95 standard and the C++ draft standard,
  I am sure you will agree that Ada95 is in no way more difficult
  to learn and implement than C++.

- Ada has some features that look complicated at first when
  you learn the language, but you have to realize that these
  features add a lot to the safety of the language.

  For instance, Ada has the following more complex mechanism
  that are much simpler in C/C++ but are much safer in Ada:

    - Much more sophisticated pointers that make dangling
      references and memory leaks much more unlikely.

    - Sophisticated arrays (slices, aggregates) make the
      dangerous memcpy/memfil/memcmp mechanisms of C
      unnecessary that escape proper type checking.

    - Ada has many features that make it easier to write code
      for which certain properties can quickly be proofen
      formally. For instance the simple fact that "for" loop
      variables are inside the block constants guarantees that
      Ada "for" loops always terminate (unless you do messy
      "unchecked" things which can easily be spotted and are
      extremely rarely necessary).

Writing verifyably correct C/C++ code is a many orders of magnitutes
more complex task than writing verifyably correct Ada code.
Therefore Ada won rather quickly the markets of safety and
security critical applications where code inspection costs much
more than code development.

Most of the negative press that Ada got before 1995 (before
Ada was revised into the modern 1995 version and before GNAT
was available) should be considered completely out-of-date
today!

Ada95 is is a modern state-of-the-art language for large
scale universal application software engineering. With some
restrictions, the same applies for Java. The Java vs. Ada
view of the industry is strongly biased by the enormous marketing
hype that has been created for Java in the context of being a
Web language. C is becoming a rather old language and seems
to slowly join Fortran and Cobol as old-fashioned but
never dieing languages. C++ suffers fundamentally from all the
problems of C and is only interesting because Microsoft supports
it well. If you look at a high-quality production language in 1998,
Java and Ada95 are the ones you should consider. The advantage
of Ada over Java is that Ada is not designed for the byte code
interpretation model. Ada software therefore executes more
efficiently and Ada in contrast to Java has excellent facilities
for low-level system programming (e.g., for writing device drivers)
and for interfacing with other programming languages (especially
C, which is important because of all the excellent C libraries
and the many C APIs out there).

I've been using C intensively for over eight years now and I
have had some experience with both C++ and Java. I am now moving
to Ada95, and so far it has been a lot of fun and a good
experience. I love C, but I am well aware of its problems, which
can be a real pain in large or safety critical applications.
I am uncomfortable with C++ and I think it is fair to describe
it more as a object-oriented luxury assembler and not as a modern
high-level programming language. Java is a neat modern
state-of-the-art language, as is Ada95. Ada95 is in some ways
less restricted than Java and certainly better suited for
low-level and system programming as well as for safety critical
systems.

Just my private experience, feel free to forward it to your boss ...

Markus

-- 
Markus G. Kuhn, Security Group, Computer Lab, Cambridge University, UK
email: mkuhn at acm.org,  home page: <http://www.cl.cam.ac.uk/~mgk25/>