Supertypes RE: Extensible Enumerated types

Supertypes RE: Extensible Enumerated types

[Robert C. Leif, Ph.D.]

From: Bob Leif
To: My fellow Ada users

This is suggestion includes the addition of a new keyword to Ada. I realize
that some would consider this rank heresy.

Since Ada has Subtypes to specify a subset of a type, it would be reasonable
to create a symmetrical operation to create a superset of a type.

-- from Package Prefix_Recs
type Prefix_Type is (None, Mr, Ms, Miss, Mrs, Dr, Prof, Rev,
    Other);

--From Package Prefix_Recs.Army
Supertype Army_Prefix_Type is (Prefix_Type, Private, Corporal, Sergeant,
Lieutenant, Captain, Major, Colonel, General);

Prefix_Type'range would also be a possibility.

Army_Prefix_Type would inherit all of the operations of Prefix_Type.

I believe that super is lexicography a better choice than supra. I must add
that supertypes are appropriate for a super language.

Re: Supertypes RE: Extensible Enumerated types

[Marin David Condic]

I could see that as interesting - sort of building onto type extension. There
may be issues with representation that need to be looked at, do you think? I
guess my only reservation would be that it needs to be asked how generally
useful is this? Would it enable some significant new technique that would get
used often enough to make it worth disturbing the reserved word list?

MDC

Robert C. Leif, Ph.D. wrote:

> From: Bob Leif
> To: My fellow Ada users
>
> This is suggestion includes the addition of a new keyword to Ada. I realize
> that some would consider this rank heresy.
>
> Since Ada has Subtypes to specify a subset of a type, it would be reasonable
> to create a symmetrical operation to create a superset of a type.
>
> -- from Package Prefix_Recs
> type Prefix_Type is (None, Mr, Ms, Miss, Mrs, Dr, Prof, Rev,
>     Other);
>
> --From Package Prefix_Recs.Army
> Supertype Army_Prefix_Type is (Prefix_Type, Private, Corporal, Sergeant,
> Lieutenant, Captain, Major, Colonel, General);
>
> Prefix_Type'range would also be a possibility.
>
> Army_Prefix_Type would inherit all of the operations of Prefix_Type.
>
> I believe that super is lexicography a better choice than supra. I must add
> that supertypes are appropriate for a super language.

--
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RE: Supertypes RE: Extensible Enumerated types

[Beard, Frank]

Bob,

I like Jeff Creem's idea of:

type Fruit_Type is (Apple, Orange);
type New_Fruit_Type is new Fruit_Type with (Pear, Kiwi);

So your example would be:

-- from Package Prefix_Recs
type Prefix_Type is (None, Mr, Ms, Miss, Mrs, Dr, Prof, Rev,
    Other);

--From Package Prefix_Recs.Army
type Army_Prefix_Type is new Prefix_Type with (Private, Corporal, Sergeant,
Lieutenant, Captain, Major, Colonel, General);

Wouldn't this serve your purposes without the need of adding a new
reserved word?

Frank


-----Original Message-----
From: Robert C. Leif, Ph.D. [mailto:rleif@rleif.com]
Sent: Wednesday, January 31, 2001 3:05 AM
To: comp.lang.ada@ada.eu.org
Subject: Supertypes RE: Extensible Enumerated types 

> This is suggestion includes the addition of a new keyword to Ada. I
realize
> that some would consider this rank heresy.
>
> Since Ada has Subtypes to specify a subset of a type, it would be
reasonable
> to create a symmetrical operation to create a superset of a type.

Re: Supertypes RE: Extensible Enumerated types

[Jeffrey Carter]

"Beard, Frank" wrote:
> I like Jeff Creem's idea of:
> 
> type Fruit_Type is (Apple, Orange);
> type New_Fruit_Type is new Fruit_Type with (Pear, Kiwi);

This seems like an excellent idea. The only difference between this and

type New_Fruit_Type is (Apple, Orange, Pear, Kiwi);

would be type conversions between the types:

F : Fruit_Type     := ...;
N : New_Fruit_Type := ...;

N := New_Fruit_Type (F); -- Always OK
F := Fruit_Type (N);     -- Raises Constraint_Error if N not in
                         -- Apple .. Orange

Are there any technical/implementation issues against this?

-- 
Jeff Carter
"We call your door-opening request a silly thing."
Monty Python & the Holy Grail

Re: Supertypes RE: Extensible Enumerated types

[Nick Roberts]

I've posted to this newsgroup elsewhere pretty much using Jeff Creem's
suggested syntax, also detailing the conversions and other issues.

--
Nick Roberts
http://www.AdaOS.org