From: Ben Laurie <ben@gonzo.ben.algroup.co.uk>
Date: Fri, 8 Nov 1996 04:24:34 -0800 (PST)
To: "Timothy C. May" <tcmay@got.net>
Subject: Re: Sliderules, Logs, and Prodigies
In-Reply-To: <v03007803aea873ff3acc@[207.167.93.63]>
Message-ID: <9611081117.aa20234@gonzo.ben.algroup.co.uk>
MIME-Version: 1.0
Content-Type: text/plain


Timothy C. May wrote:
> 
> 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.

I think claiming RPN for Forth is pushing it a little far. Admittedly it is
stack-based (well, two-stack-based), and everything an operator can operate on
is to the left, but the provision of arbitrary stack manipulation, "compile"
mode (triggered by the '[' operator, if my memory serves) and so on make it
rather a different beast.

Incidentally, PostScript is Forth in disguise.

Cheers,

Ben.

-- 
Ben Laurie                Phone: +44 (181) 994 6435  Email: ben@algroup.co.uk
Freelance Consultant and  Fax:   +44 (181) 994 6472
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