Re: Consider her way -- Re: Dimensionality Checking

["Alexandre E. Kopilovitch" <aek@vib.usr.pu.ru>]

"Mark Lundquist" <no.spam@getalife.com> wrote:
>you have to hand-code all needed conversions for base
>and derived units (vs. defining them for a handful of base units).  Nor are
>they reversible, i.e. for interoperability between m and km I would have to
>write the conversion going each way rather than simply defining the
>relationship between them.

So you are going to introduce the explicit relationships between the types,
and some reduction rules for the statements such as
  Variable := Expression;
- right? Hmm, that will be a great job, substantial innovation, and will produce
a visible impact on the whole Ada core language. The applications of that new
feature surely will not be restricted to the unit conversions.

>> > in this regard (unit abstraction for numeric types).
>> By the way, I still don't see an abstraction here. How will you describe the
>> notion of unit as an abstraction? For example "a type is the set of possible
>> values and the set of operations" - and what is a unit?
>
>Well, what is a "value"? :-)

No problem. Let us be slightly more formal: "a type is an ordered pair of the
sets; the elements of the first set are called the values of this type; the
elements of the second set are subroutines, and they are called the operations
of this type".

>The concept of
>unit, like that of value, is not "definable" in the language, but that is
>not necessary.  You're getting all philosophical about it and making it
>harder than it really is :-).  But I certainly do see an abstraction in units...

In such a case, perhaps you are able to describe - more or less formally -
that abstraction, which you see here?


Alexander Kopilovitch                      aek@vib.usr.pu.ru
Saint-Petersburg
Russia