[Oberon] Numerical CASE Statements in Project Oberon

[Jan de Kruyf]

Yes,
The old man has been right most of the time, I agree. And I will have a
royal battle to reduce the compiler construction back down to Wirthian
elegance, that I also realize. But at the same time the code I produce is
very elegant and sweet. On the basis of that I would say you are wrong in
your statement that IF THEN can be made as efficient as a good case
construct. Besides, a Case statement allows ranges like A..Z, a..z and so
on, this has never been part of IF THEN, while in a properly constructed
bin-tree it resolves itself.

So since Wirth was first and foremost a teacher all his life, we could say
that there are 2 learning opportunities here
1. to produce fast code.
2. to construct an elegant way of doing so.

 I think that the master himself also realized the issues you and I are
bringing up, and did not see his way out of the predicament yet. And since
he is about 80 now and since he still got a few irons in the fire this was
left for a bit.

Lastly Dijkstra taught that you should never limit yourself because of
inefficient machines. But you should strive to generalize any language
design solution to as many cases as possible, even if that slows your
program execution down a bit. There were big arguments in the Algol design
meetings about that. Some people then felt that you had to live with the
equipment given and use it as efficiently as possible. Wirth no doubt knows
that whole history even better than I do. In the mean time of course, the
machine limitations of those days (it was the time of the vacuum tubes)
have been solved a hundred times over, but we still are trying to live with
the language limitations of some of the older languages.
Ergo the numerical case statement is in the O-7 language report, but is has
not been implemented yet.

So I feel fully justified implementing it. The way how to, we can talk
about. If the Oberon community is alive and well ten I am sure that the
last word has not been spoken yet.


Enjoy your day

j.




On Tue, Nov 10, 2015 at 3:23 PM, John Stout <JSS at kgv.ac.uk> wrote:

> I wonder what Professor Wirth’s views might be on this.
>
>
>
> From the book The School of Niklaus Wirth (>> The Art of Simplicity<<)
> ISBN 1-55860-723-4, the chapter by Michael Franz called Oberon – The
> Overlooked Jewel:
>
>
>
> “I still vividly remember the day that With decided to replace the elegant
> data structure used in the compiler’s symbol table handler by a mundane
> linear list. In the original compiler, the objects in the symbol table had
> been sorted in a tree data structure (in identifier lexical order) for fast
> access, with a separate linear list representing their declaration order.
> One day Wirth decided that there really weren’t enough objects in a typical
> scope to make the sorted tree cost-effective. All of us Ph.D. students were
> horrified: it had taken *time* to implement the sorted tree, the solution
> was *elegant*, and it worked *well* – so why would one want to throw it
> away  and replace it with something *simpler*, and even worse, something
> as prosaic as a linear list? But of course, Wirth was right, and the
> simplified compiler was both smaller and faster than its predecessor.”
>
>
>
> The implementation using IF … THEN chains is simple. If the most common
> cases are positioned first in the chain then the execution time for these
> cases is minimised. The compiler will be simpler, the implementation of the
> ELSE (or an error) is simple to implement and the compiler will be simple
> and fast.
>
>
>
> Looking through the body of Oberon code that we have what is the
> distribution of the number of cases? I realise we are talking about a new
> feature, but I still favour the simple solution, in keeping with the spirit
> of Oberon.
>
>
>
> John Stout
>
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