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Date: Tue, 3 Dec 2019 09:02:46 -0800 (PST)
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Subject: Re: Beginning Ada Programming, by Andrew T. Shvets (2020)
From: Shark8 <onewingedshark@gmail.com>
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Xref: reader01.eternal-september.org comp.lang.ada:57641
Date: 2019-12-03T09:02:46-08:00
List-Id: <comp.lang.ada>

On Tuesday, December 3, 2019 at 9:50:40 AM UTC-7, Lucretia wrote:
>=20
> I said to introduce them to typing concepts after getting them used to th=
e very basics, i.e. first few simple programs adding numbers and printing t=
hem 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 modeli=
ng 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 =3D> Symbol in '!'|'@'|'#'|'$'|'%'|'^'|'&'|'*';

Minimum_Length : Constant :=3D  8;
Maximum_Length : Constant :=3D 32;

Type Password is new String
  with Dynamic_Predicate =3D> Password'Length in Minimum_Length..Maximum_Le=
ngth=20
    and (For all C of Password =3D> C in Digit|Upper_Case|Lower_Case|Symbol=
);

You can then explain what each of these are ans how they compose the type P=
assword that is guaranteed by the type-system to have the modeled propertie=
s.