Re: Ada Successor Language

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

On 2018-06-19 23:07, Dan'l Miller wrote:
> On Tuesday, June 19, 2018 at 2:39:30 PM UTC-5, Dmitry A. Kazakov wrote:
>> On 2018-06-19 21:19, Paul Rubin wrote:
>>> "Dmitry A. Kazakov" writes:
>>>> There are 50 shades of mess. Ada's generics try to introduce some
>>>> weakly-typed contracts on the formal generic parameters, where C++
>>>> templates go completely untyped, but mess is always mess. You cannot
>>>> make a decent language out of macro processor.
>>>
>>> I don't understand what you're getting at.  Are Ada generics implemented
>>> with a macro processor?  C++ templates amount to that, but there are
>>> other, better ways to implement generics.
>>
>> Generics and macros are same thing regardless implementation. The core
>> idea and all power lies in textual substitution as opposed to the
>> concept substitutability in a properly typed systems.
> 
> Clearly, Ada's generics are not performing textual substitution.  Ada's generics are performing constraint-matching on subtypes passed as formal arguments.  If the criteria of the constraints are satisfied, the previously-declared-long-ago subtype in the AST is what is passed in as the formal argument of an Ada generic.

There is no such thing in Ada. Formal generic types, e.g.

    type Foo (<>) is private;

match pretty much anything. The actual type is then substituted in all 
language constructs just like macros do. The only constraint here is the 
language syntax and a few sematic checks which make the language of 
generics (not to confuse with the core language) weakly typed, where C++ 
templates are completely untyped.

> I hope that you don't say for 25 would-be passings of different subtypes in as the formal argument of a single would-be generic package's type parameter that a human being should manually author the same or nearly the same differently-named packages 25 times (and get carpal-tunnel syndrome).

Certainly I do. Subtypes in Ada are directly substitutable. You need 
just one body:

    procedure Foo (X : Integer); -- You can use any Integer subtype here

I you meant rather *types*, then as I said earlier, polymorphism can be 
achieved by different means and ad-hoc polymorphism offered by generics 
the worst possible way. My point was to use dynamic polymorphism instead.

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