Re: "functional" programming in Ada

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 08/03/2018 04:34, Randy Brukardt wrote:
> "Pascal Obry" <pascal@obry.net> wrote in message
> news:1520428274.2488.155.camel@obry.net...
> Le mercredi 07 mars 2018 à 02:52 -0800, Mehdi Saada a écrit :
>>> Why not writing everything in the specs then ? Maybe the original
>>> separation of specs and bodies is a mistake, in the light of recent
>>> tools requirements.
>>
>> The spec is what is exposed to other units.
>>
>> The body is implementation details.
>>
>> The separation is to me one of the most important point in Ada. I think
>> that all languages should have done that. It is an welcomed separation
>> for software engineer.
> 
> Right. And note that the specification has always contained elements which
> are determined at runtime (that is, executed). For instance, even in Ada 83
> you could have a subtype like:
> 
>        subtype Dyn is Natural range 1 .. Some_Function;
> 
> and to properly export Dyn, one has to execute code.

Determined at run-time /= determined in a specific way. Even if 
evaluation of an expression is static, when that expression is an 
implementation, that thing has *nothing* to seek in the specifications. 
Specifications must be only specifications regardless when and how 
evaluated.

> The various contracts (preconditions, postconditions, predicates, etc.) all
> contain some executable code, and it is necessary for callers to be able to
> understand those contracts. Expression functions help in this, while the
> bulk of the implementation should remain in the body.

These are not contracts if have any executable code, and more 
importantly, understanding cannot be achieved by exposing 
implementation/code.

P.S. Contracts exist prior the program (programs, actuall) and surely 
prior to any execution of (any implementation of any programs under the 
contract).

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de