Re: Beginning Ada Programming, by Andrew T. Shvets (2020)

[Shark8 <onewingedshark@gmail.com>]

On Tuesday, December 3, 2019 at 9:50:40 AM UTC-7, Lucretia wrote:
> 
> I said to introduce them to typing concepts after getting them used to the very basics, i.e. first few simple programs adding numbers and printing them out, how the build using the compiler, then handle types and explaining how they're different to something like typedef in C.

Perhaps the easiest way to do this is by doing something that's (e.g.) much more complex in C, but relatively straightforward in Ada -- perhaps modeling a Password in the software:

Type Digit      is Character Range '0'..'9';
Type Upper_Case is Character Range 'A'..'Z';
Type Lower_Case is Character Range 'a'..'z';
Type Symbol is Character
  with Static_Predicate => Symbol in '!'|'@'|'#'|'$'|'%'|'^'|'&'|'*';

Minimum_Length : Constant :=  8;
Maximum_Length : Constant := 32;

Type Password is new String
  with Dynamic_Predicate => Password'Length in Minimum_Length..Maximum_Length 
    and (For all C of Password => C in Digit|Upper_Case|Lower_Case|Symbol);

You can then explain what each of these are ans how they compose the type Password that is guaranteed by the type-system to have the modeled properties.