"Strong typing vs. strong testing"
Tim Bradshaw
tfb at tfeb.org
Tue Sep 28 16:55:26 CEST 2010
On 2010-09-28 14:39:27 +0100, Malcolm McLean said:
> he problem is that if you allow expressions rather than terms then
> the experssions can get arbitrarily complex. sqrt(1 inch + 1 Second),
> for instance.
I can't imagine a context where 1 inch + 1 second would not be an
error, so this is a slightly odd example. Indeed I think that in
dimensional analysis summing (or comparing) things with different
dimensions is always an error.
>
> On the other hand sqrt(4 inches^2) is quite well defined. The question
> is whether to allow sqrt(1 inch). It means using rationals rather than
> integers for unit superscripts.
There's a large existing body of knowledge on dimensional analysis
(it's a very important tool for physics, for instance), and obviously
the answer is to do whatever it does. Raising to any power is fine, I
think (but transcendental functions, for instance, are never fine,
because they are equivalent to summing things with different
dimensions, which is obvious if you think about the Taylor expansion of
a transcendental function).
--tim
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