Re: Extending discriminant types

[Martin <martin.dowie@btopenworld.com>]

On Nov 20, 10:59 pm, a...@anon.org (anon) wrote:
[snip]
> Now to the RM.
>
> From the RM 95, Annex N:
>
> 38   Subtype.  A subtype is a type together with a constraint, which
> constrains the values of the subtype to satisfy a certain condition.  The
> values of a subtype are a subset of the values of its type.
>
> With that in mind. The definition of the "Base attribute" in Annex K:
>
> 18   S'Base denotes an unconstrained subtype of the type of S. This
>      unconstrained subtype is called the base subtype of the type.
>      See 3.5.
>
> and from RM 3.5
>
> S'Base:  denotes an unconstrained subtype of the type of S. This
>          unconstrained subtype is called the base subtype of
>          the type.
>
> Also Annex K says "For every scalar subtype S:" it does not say for
> "For every scalar subtypes S only:".

But the section heading for 3.5 kind of gives it away doesn't
it..."Scalar Types"! If it applied to other kinds of type then it
would be mentioned in those sections.

And why would K(17) have to include the word "only" when it already
includes "scalar"?

None of the other entries in Annex K use "only" to limit their
applicability - they just state what they are applicable to. Would you
really then read on from K(17) and think K(19) "S'Bit_Order For every
specific record subtype S:" means that 'Bit_Order could apply to
something other than a record subtype??? Or K(181) 'Pred applies to
something other than scalars??? etc

Cheers
-- Martin