Re: Anybody in US using ADA ? One silly idea..

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

Hyman Rosen wrote:

> Dmitry A. Kazakov wrote:
>> I think I explained why. But to avoid that discussion again, just take
>> the unit solution for C++ you mentioned and try to implement a calculator
>> for dimensioned values using it.
> 
> No, I don't want to do that. If I did want to do that,
> my solution would be inappropriate, but so what?

It is not a universal solution. That's the point. A floating-point type is 
one for real logarithmic values. Are you sure that dimensioned values have 
no universal solution at all?

> Part
> of designing a program is deciding what is fixed at
> compile-time and what is decided at run-time.

Yes, but sometimes it is the language that forces you to decide. The 
question is again, is that a cruelty of the Universe or just an arbitrary 
defect of a particular language.

> Ada has ranged types where the ranges are fixed at compile-time,

They are not, up to some limit. But the problem is whether the language 
gives you an opportunity to define new numeric types without the 
restrictions you do not need and close enough to the theoretical 
performance limit for the remaining restrictions. Ada almost can this. 
[Almost, because one cannot make a private type "numeric" for the 
compiler.]

> and records whose field names are fixed at compile-time,
> and procedures whose parameters are fixed at compile-time.

It is not very useful, I mean untyped containers if you point at that. What 
can you do with the elements of an "unknown" type? Only put them into 
another container. Ada is not Lisp.

> Similarly, it has generics whose parameters are fixed at
> compile-time. When I know what I need at compile-time,
> why should I be required to funnel it through a mechanism
> which is designed for run-time variation?

No, this is wrong. This mechanism and generics are both designed *just* for 
variation. The nature of generics excludes run-time variation. This is a 
restriction. If you are trying to defend this restriction, then well, I 
admit that there are useful restrictions, but I see no advantages in this 
case. It is same as to claim that:

generic
   Size : Natural;
package ... is
   type My_String is record
      Text : String (1..Size);
   end record;

is better than

   type My_String (Size : Natural) is record
      Text : String (1..Size);
   end record;

Dispatching, discriminants, array bounds have no such restiriction. Moreover 
subtyping/subclassing enrich the structure of types, while generics just 
ignore types and relations between them. What's the use of a variation over 
a type set if you are unable to specify an element of the set?

-- 
Regards,
Dmitry A. Kazakov
www.dmitry-kazakov.de