From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,FREEMAIL_FROM
	autolearn=unavailable autolearn_force=no version=3.4.4
X-Received: by 2002:a05:620a:1366:: with SMTP id
 d6mr28349065qkl.114.1590437758395;
        Mon, 25 May 2020 13:15:58 -0700 (PDT)
X-Received: by 2002:aca:88c:: with SMTP id 134mr7493114oii.99.1590437758049;
 Mon, 25 May 2020 13:15:58 -0700 (PDT)
Path: 
 eternal-september.org!reader01.eternal-september.org!feeder.eternal-september.org!news.gegeweb.eu!gegeweb.org!usenet-fr.net!proxad.net!feeder1-2.proxad.net!209.85.160.216.MISMATCH!news-out.google.com!nntp.google.com!postnews.google.com!google-groups.googlegroups.com!not-for-mail
Newsgroups: comp.lang.ada
Date: Mon, 25 May 2020 13:15:57 -0700 (PDT)
In-Reply-To: <871rnk97ew.fsf@nightsong.com>
Complaints-To: groups-abuse@google.com
Injection-Info: google-groups.googlegroups.com; posting-host=76.121.70.69;
 posting-account=pQzPUgkAAAAOiiJHd16-n1B6leDCaI3_
NNTP-Posting-Host: 76.121.70.69
References: <d4cc5c66-b82a-4ef7-8e69-2fa9b7bd99a6@googlegroups.com>
 <r9mp29$6nd$1@dont-email.me>
 <3c545096-d000-4d09-b3fe-ad8530632457@googlegroups.com>
 <871rnk97ew.fsf@nightsong.com>
User-Agent: G2/1.0
MIME-Version: 1.0
Message-ID: <14afb70d-cb70-4ca2-bd24-f9d9664ee103@googlegroups.com>
Subject: Re: Implicit actions & program correctness
From: deadhacker <gstover@gmail.com>
Injection-Date: Mon, 25 May 2020 20:15:58 +0000
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Xref: reader01.eternal-september.org comp.lang.ada:58787
Date: 2020-05-25T13:15:57-07:00
List-Id: <comp.lang.ada>

On Friday, May 15, 2020 at 3:10:02 PM UTC-7, Paul Rubin wrote:
> You might like this article (not Ada specific):
>=20
> http://blog.tmorris.net/posts/understanding-practical-api-design-static-t=
yping-and-functional-programming/

Paul, thank you so much for the link.  It's good reading.

To me, seems that his third requirement is the tough one.  (Quoting it here=
: "If I call move on a tic-tac-toe board, but the game has finished, I shou=
ld get a compile-time type-error. In other words, calling move on inappropr=
iate game states (i.e. move doesn=E2=80=99t make sense) is disallowed by th=
e types.")

It seems that if I have a Move subprogram that operates on a Game, it & pro=
duces another Game, I don't see how it could sometimes return a FinishedGam=
e that can be detected at compile-time.  (It could return a Game that could=
 be checked for Finished at run-time.)

Sadly, his Java API is no longer available, so I can't see how he solved it=
.

Do you (or anyone else here) know how it could be solved with Ada?