Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!decwrl!decvax!ima!haddock!karl
From: karl@haddock.ima.isc.com (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: When is a cast not a cast?
Message-ID: <13189@haddock.ima.isc.com>
Date: 19 May 89 03:01:30 GMT
References: <2747@buengc.BU.EDU> <10191@smoke.BRL.MIL> <406@skye.ed.ac.uk> <10276@smoke.BRL.MIL> <2890@buengc.BU.EDU> <546@TSfR.UUCP> <2908@buengc.BU.EDU>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 20

(This is not a flame.  If this continues to the point where I feel compelled
to flame, you'll recognize it as such.)

This is a lot like talking to the platygaeanists in talk.origins.  It's hard
to refute you without knowing what you already accept.

Blair, do you understand that, even though one commonly represents both points
and vectors as n-tuples of numbers, that they are conceptually different?  Do
you accept the (common and useful) laws of arithmetic for points and vectors?

(A point has a position; a vector has a magnitude and direction.  Adding or
subtracting vectors gives you another vector.  Adding a vector to a point
gives you another point.  Subtracting two points gives you a vector.)

Does it bother you that when you multiply two lengths, you get an area rather
than another length?  Or that the ratio of two lengths is dimensionless?
Pointers are additive rather than multiplicative, but the principle is the
same.

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint