Path: utzoo!utgpu!watserv1!watmath!att!ima!haddock!karl
From: karl@haddock.ima.isc.com (Karl Heuer)
Newsgroups: comp.lang.misc
Subject: Re: Typing on units
Message-ID: <16248@haddock.ima.isc.com>
Date: 21 Mar 90 21:41:05 GMT
References: <39941@ism780c.isc.com> <883@enea.se> <40346@ism780c.isc.com> <907@enea.se>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Cambridge, MA 02138-5302
Lines: 23

In article <907@enea.se> sommar@enea.se (Erland Sommarskog) writes:
>Marvin Rubenstein (marv@ism780.UUCP) writes:
>>[about having dimensional analysis built into a language]
>
>I was fully aware of what I proposed was not really what you wanted,
>on the other hand, I don't see any important conceptual difference
>in your out-line. Your notation is far more compact that the Ada
>package you would have to write, but once you would had it done,
>you could go ahead and program your computation. And the package
>would still be there the next time.

The problem is that there are a *lot* of distinct types: a true dimensional
analysis language would accept "meter^3/(kilogram*second^2)" automatically; in
Ada it works only if the package author had the foresight to include it.

>[One pitfall in Ada is that you] have to rely on a conversion routine:
>   Real_world_distance := Feet_to_meter(US_distance);

Or just use a predefined constant of the appropriate type:
    Real_world_distance := METERS_PER_FOOT * US_distance;
since the dimensional analysis will keep you from doing it backwards.

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