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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: S-expression I/O in Ada
Date: Mon, 09 Aug 2010 17:34:34 -0400
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2010-08-09T17:34:34-04:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

>>> 2. No ranges
>>> 3. No loops
>> 
>> I don't know what you want ranges and loops for.
>
> A subset of flags. E.g. Critical_Errors, Warnings, Any_Error.

I don't understand this part.  If subrange of a modular type
used as a bit map is not a coherent subset of the flags.

> Yes, it is a type property that the domain is a set of identifiable values,
> in fact, some mapping to an enumeration.
>
> The language should provide means to implement this interface with any
> type. E.g. why I cannot specify this interface for String to be able to
> write:
>
>    case Get_Token is
>        when "type" => ...
>        when "package" => ...
>        when others => raise Syntax_Error;
>    end case;

It would be nice.

>> But no Ada compilers support this:
>> 
>>     type Bit_Map is mod 2**100;
>
> Why not? It is not that difficult to implement mod 2**100 or range
> -2**1_000_000..2**1_000_000+1. I think the standard should require it on
> any hardware.

I agree.  But you and I are in a small minority here!

The frustrating thing to me is that every Ada compiler must support
arbitrary-range integer arithmetic at compile time, but can't make
that available in a portable way at run time.

- Bob