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Subject: Re: Quality systems (Was: Using Ada for device drivers? (Was: the
       Ada mandate, and why it collapsed and died))
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Date: Wed, 28 May 2003 18:56:03 +1200
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Xref: archiver1.google.com comp.lang.ada:37875
Date: 2003-05-28T18:56:03+12:00
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"Marin David Condic" <nobody@noplace.com> wrote in message
news:3ED353BE.40605@noplace.com...
> Pretty simple stuff. Suppose you had a type like:
>
> type Saturated_Integer is range -10..10 ;
>
> and an object of that type such as:
>
> X : Saturated_Integer := 9 ;
>
> and then:
>
> X := X + 4 ;
>
> would mean:
>
> (X = 10)
>
> and later you might do:
>
> X := X - 25 ;
>
> and you get
>
> (X = -10)

But that means that something somewhere
must have an actual counter which keeps
the actual value of what you pretend is
a saturated integer. After all, you, as
the user of the saturated type, don't
(or shouldn't) know if one saturated
number is equal to another - they are
all equal in a sense. But whatever
implements them obviously must. So,
what about this (assuming X is already
saturated and Y is the largest unsaturated
number):

if Y = X - 1 then

Should that tell me I've got the smallest
saturated number? Can I then count them?
(I've got the smallest number and I have
"+", "-", "<", ">" etc) - looks like an ordinary
integer now. Almost.

Can I do something like

for I in X..Y  ? What would that do if
there are several saturated values in that
range?

It looks like what you describe is just
a simple matter of having a much wider
actual range but providing some sort
of a checked conversion/mapping
which just does the range checking
on the number and overrides it with
a limit if needed..

It's not hard to implement either
as a custom code or some utility
library. However, pushing it onto
the compiler seems to open all
kinds of semantic cans of worms.

Unless I misunderstood your
point of course.