From: "Timothy C. May" <tcmay@got.net>
Date: Thu, 7 Nov 1996 21:30:08 -0800 (PST)
To: cypherpunks@toad.com
Subject: Re: Sliderules, Logs, and Prodigies
In-Reply-To: <Pine.LNX.3.94.961107043646.339A-100000@random.sp.org>
Message-ID: <v03007803aea873ff3acc@[207.167.93.63]>
MIME-Version: 1.0
Content-Type: text/plain


At 10:33 AM -0800 11/7/96, Dale Thorn wrote:

>According to HP, the "Polish" part of the term comes from a Polish
>mathematician whose
>name (I can't spell it, and I don't have the .DOC) is pronounced phonetically:
>WOOCASHEVITZ.  The "reverse" part apparently means the inventor specified the
>operation before the parameters, instead of how HP implemented it.


Lucaciewicz, as I recall. His notation was originally that one would add
two numbers, a and b, as "+ a b." A modified form, adapted for stack
machines, was to add two numbers with "a b +." Hence, _reverse_ Polish
notation, but equally sound.

This involves entering a, then pushing it onto the stack with an ENTER,
then entering b, then hitting the "+" key to pop the stack and place the
sum in the main (X) register.

For people who claim that (6 + 7) * 5 is the "natural" way to do things, I
point out to them that the way one does it one's head is to take 6 and 7
and add them then to multiply by 5. Or I show them

   6
+  7
-----
   13
*   5
-----
   65

Then they see that RPN is actually the way we do things in our head. Or on
paper.

Computers do things with parentheses, we don't.

By the way, Polish notation is how LISP evaluates expressions. E.g.

(+ 6 7)

or, for the full problem above,

(* 5 (+ 6 7))

And for those of you are not LISP or Scheme fans, the language FORTH also
uses Polish notation. RPN, in fact.



--Tim May



"The government announcement is disastrous," said Jim Bidzos,.."We warned IBM
that the National Security Agency would try to twist their technology."
[NYT, 1996-10-02]
We got computers, we're tapping phone lines, I know that that ain't allowed.
---------:---------:---------:---------:---------:---------:---------:----
Timothy C. May              | Crypto Anarchy: encryption, digital money,
tcmay@got.net  408-728-0152 | anonymous networks, digital pseudonyms, zero
W.A.S.T.E.: Corralitos, CA  | knowledge, reputations, information markets,
Higher Power: 2^1,257,787-1 | black markets, collapse of governments.
"National borders aren't even speed bumps on the information superhighway."