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From: tmoran@acm.org
Newsgroups: comp.lang.ada
Subject: Re: Expressing physical units (Was: Reprise: 'in out' parameters for
 functions)
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>example. When you divide a type by the same type, you get a
>dimensionless number. Multiplication of like types is prohibited
   A "dimensionless number" still has a specific type so that
  alpha : degrees;
  x,y   : feet;
  beta  : radians := x/y+alpha;
is illegal.  So the type system does more than simply keep track of
a set of exponents.

>You then define operators for all the likely operations among these
>types. Each type can be added to or subtracted from its own type, for
  See, for instance, chapter 2 of "Ada in Action" by Do-While Jones,
ISBN 0-471-6078-8, Wiley, 1989 (also available on the internet but I don't
have the URL).