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Date:	Thu, 7 Aug 2003 00:24:58 PDT7
From:	Peter Skye <pskye@peterskye.com >
Reply-To:	scoug-programming@scoug.com
To:	scoug-programming@scoug.com
Subject:	SCOUG-Programming: Re: Warpstock 2003 Presentation

Content Type: text/plain

Lynn H. Maxson wrote:
>
> "...But I don't understand what you've said in the above
> paragraph."
>
> RPN allows you to write parenthesis-free expressions. It
> does so in a manner which minimizes register usage (load
> and store). Thus it produces an optimal code sequence.

Okay, I follow you now. I wrote a PL/I routine many years ago to
convert parenthesized mathematical expressions to RPN, and just a few
years ago I used a similar idea to write a Pascal routine which
evaluated parenthesized Boolean search expressions.

I don't recall ever seeing a proof that the code was optimal, though I
take for granted that it is.

> as one IBM engineer noted the entire stack architecture
> of the Burroughs machine required all of three 7090
> instructions, two of which were "load register" and
> "store register". The third eludes me.

Probably the actual operator, yes?

> Perhaps the best overall description exists in W. H.
> Burge's "Recursive Programming Techniques" in describing
> a SECD machine (Stack, Environment, Control, and Dump).

15-20 years ago I studied up on one manufacturer's RISC offering. (The
processor might have been called a 2700 or 2900.) It had 96 registers
so you wouldn't have to access memory very often.

Then there are the coprocessors that just crunch numbers.

> I might hold out for use of English as a specification
> language. Until then my general reaction is no, no, no
> ... and no. Blair talks about ambiguity. Ambiguity
> itself represents an extension to operator overload.

Aha! Then I _finally_ understand why our elected politicians accomplish
less than a GWBASIC program. After all, they talk an awful lot. In
English.

I still see a benefit in using English, however. Suppose I'm building a
computerized lawnmower and I want to specify the desired grass height:

DCL GrassHeight float
min("crunchy feel")
max( min("water ration","fertilizer burn") );

Betcha had to read that twice! In English it's so simple: Let the
grass grow until it feels crunchy in your bare feet, don't let it get so
long that I exceed the county-imposed water rationing, and don't let it
get so long that the required fertilizer results in burn spots.

- Peter

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