Re: Quantified Expressions: "some"

["Peter C. Chapin" <pcc482719@gmail.com>]

On 2010-11-18 08:24, Niklas Holsti wrote:

>> Use a colon or double colon:
>>
>> ( for all X in 1 | 3..5 | F'Range :: P(X) )
> 
> I like that. The double-colon is visually more apparent than '|' and
> there is no risk of confusion with the earlier and other meanings of
> "=>". A single colon could also work, if we don't want to add new lexemes.

I spent some time this morning reading the email discussions associated
with AI05-0176 here

http://www.ada-auth.org/cgi-bin/cvsweb.cgi/ai05s/ai05-0176-1.txt?rev=1.17

The ARG has clearly (and not surprisingly) already considered many
issues. I'd encourage anyone interested in this subject to review the
extensive discussion before speculating on alternative syntax, etc.

For example on February 24, 2010 Edmond Schonberg says,

"Slight preference for colon in this context, but that would conflict
with the new iterator syntax, where we could say:

    for all X : T of C : P (X)

which is definitely confusing.  So right arrow may be the obvious choice."

I don't know if the "new iterator syntax" is still valid but I can
certainly see how the ':' might be a less than ideal choice in the
example above.

John Barnes outlines his objection to the vertical bar in a message
dated September 15, 2010. Two of his objections would also apply to ':'
as well ("too weak a symbol" and "=> is better because SPARK uses the
same symbol for the same purpose.")

Peter