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Re: prefix notation question

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From	Jussi Piitulainen <jpiitula@ling.helsinki.fi>
Newsgroups	comp.lang.java.programmer
Subject	Re: prefix notation question
Date	17 Oct 2011 10:06:25 +0300
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Chad <cdalten@gmail.com> writes:

> On Oct 16, 8:46 pm, Peter Duniho <NpOeStPe...@NnOwSlPiAnMk.com> wrote:
> > On 10/16/11 8:15 PM, Chad wrote:
> >
> > > I'm supposed to write a program that calculates arithmetic expressions
> > > using prefix notation. The one example our professor gave us is
> >
> > > (+ (- 6) (* 2 3 4) (/ (+ 3) (* 1) (- 2 3 1)))
> >
> > > Which evaluated sucessively becomes..
> >
> > > (+ (- 6) (* 2 3 4) (/ 3 1 -2)) //<----I don't see how he arrives at
> > > this expression
> > > (+ -6 24 -1.5)
> > > 16.5
> >
> > > I don't see how he gets (+ (- 6) (* 2 3 4) (/ 3 1 -2)) from (+ (- 6)
> > > (* 2 3 4) (/ (+ 3) (* 1) (- 2 3 1)))
> >
> > Ask your professor.
> 
> I did. He told me to come by during his office hours. I told him I
> couldn't because of work. He hasn't responded back.
> 
> Chad

In (/ 3 1 -2), divided 3 by 1 and -2. Similarly in (- 2 3 1), subtract
3 and 1 from 2. This is the rule for two or more arguments to / and -.

With one argument, like in (- 6), the rule is different and the
notation means the appropriate inverse: additive inverse in case of -,
multiplicative in case of /.

The languages that use this notation tend to like -3/2 (an exact
rational computed from exact rationals) more than -1.5 (typically an
approximation).

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prefix notation question Chad <cdalten@gmail.com> - 2011-10-16 20:15 -0700
  Re: prefix notation question Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-10-16 20:46 -0700
    Re: prefix notation question Chad <cdalten@gmail.com> - 2011-10-16 20:58 -0700
      Re: prefix notation question Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-10-16 23:38 -0700
      Re: prefix notation question Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-10-17 10:06 +0300
        Re: prefix notation question Chad <cdalten@gmail.com> - 2011-10-17 07:39 -0700
          Re: prefix notation question Chad <cdalten@gmail.com> - 2011-10-17 07:45 -0700
            Re: prefix notation question Chad <cdalten@gmail.com> - 2011-10-17 07:50 -0700
              Re: prefix notation question Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-10-17 18:10 +0300
                Re: prefix notation question Chad <cdalten@gmail.com> - 2011-10-18 15:30 -0700
                Re: prefix notation question Roedy Green <see_website@mindprod.com.invalid> - 2011-10-18 19:40 -0700
  Re: prefix notation question Roedy Green <see_website@mindprod.com.invalid> - 2011-10-18 19:36 -0700

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