Re: Ada's ranking of popularity at IEEE Spectrum

[Shark8 <OneWingedShark@gmail.com>]

On 08-Jul-14 17:03, sbelmont700@gmail.com wrote:
> So we, as a community, cannot easily divide up the work in a component like manner,
> and are usually forced to start all way down at the O/S interface level *for every
> single project*.

Why would we need to start at the OS level for TLS? Yes, I realize we'll 
need to depend on X.509 and ASN.1, but I don't see why we cannot write 
[at least those] in a generally platform-independent manner.

In fact, given Ada's reputation as being highly-portable, wouldn't 
writing theses basic [fundamental, not simple] components be a /good/ thing?

> And again, even if you do manage to create an elegant Ada interface to OpenSSL,
> it's not going to be OpenSSL, because OpenSSL is an untyped C API that is anathema
> to everything Ada.  The better you make it, the further away from the standard you
> get, and the less people are going to want to use it.

I said TLS, not OpenSSL.
But even so, what's stopping someone from taking a formally-verified TLS 
component and wrapping/exporting it for C [and OpenSSL] compatibility? 
How would that be buying into C's type-system?

e.g. what is stopping us from exporting to C-interface if we have a 
string-date package? Sure values and such won't be protected on the 
C-side, but we know about out Ada side, no?

Package Date_String is

     -- Date-String format: ####-##-##
     Subtype Date_String is String(1..10)
     with Dynamic_Predicate =>
       (for all Index in Date_String'Range =>
          (case Index is
             when 5|8  => Date_String(Index) = '-',
           when others => Date_String(Index) in '0'..'9'
          )
       ) and then -- short-circut boolean, ensures the above first
       (case Month(Date_String) is
          when 1 | 3 | 5 | 7 | 8 | 10 | 12 => Day(Date_String)'Valid,
          when 4 | 6 | 9 | 11              => Day(Date_String) in 1..30,
          when 2 => (if Is_Leap_Year(Date_String) then Day(Date_String) 
in 1..30
                     else Day(Date_String) in 1..29)
       );

     SUBTYPE C_Date_String is Interfaces.C.Strings.char_array_access with
       Dynamic_Predicate =>
           Interfaces.C.To_Ada(C_Date_String.All) in Date_String;

     -- Whatever procedures we need to export.

Private

        Subtype Month_Type is Natural range 1..12;
        subtype Day_Type   is Natural range 1..31;

     Function Year ( Input : String ) Return Natural is
       ( Natural'Value(Input(Input'First..Input'First+3)) );
     Function Month( Input : String ) Return Month_Type is
       ( Natural'Value(Input(Input'First+5..Input'First+6)) );
     Function Day  ( Input : String ) Return Day_Type is
       ( Natural'Value(Input(Input'Last-1..Input'Last)) );

     -- METHOD FOR DETERMINING LEAP-YEAR:
     -- (1) If the year is evenly divisible by 4, go to step 2.
     --     Otherwise, go to step 5.
     -- (2) If the year is evenly divisible by 100, go to step 3.
     --     Otherwise, go to step 4.
     -- (3) If the year is evenly divisible by 400, go to step 4.
     --     Otherwise, go to step 5.
     -- (4) The year is a leap year (it has 366 days).
     -- (5) The year is not a leap year (it has 365 days).
     --
     -- CONCISELY:
     --     Year Mod 400 = 0 or (Year Mod 4 = 0 and Year Mod 100 /= 0)
     Function Is_Leap_Year( Year : Natural ) Return Boolean is
       (Year Mod 400 = 0 or (Year Mod 4 = 0 and Year Mod 100 /= 0));
     Function Is_Leap_Year( Input : String  ) Return Boolean is
       ( Is_Leap_Year(Year(Input)) );

End Date_String;