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 10.107.147.136 with SMTP id v130mr7294945iod.28.1472322363061;
        Sat, 27 Aug 2016 11:26:03 -0700 (PDT)
X-Received: by 10.157.6.44 with SMTP id 41mr704269otn.10.1472322363038; Sat,
 27 Aug 2016 11:26:03 -0700 (PDT)
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!feeder.eternal-september.org!news.glorb.com!x131no468162ite.0!news-out.google.com!d68ni40892ith.0!nntp.google.com!j128no468897ith.0!postnews.google.com!glegroupsg2000goo.googlegroups.com!not-for-mail
Newsgroups: comp.lang.ada
Date: Sat, 27 Aug 2016 11:26:02 -0700 (PDT)
Complaints-To: groups-abuse@google.com
Injection-Info: glegroupsg2000goo.googlegroups.com;
 posting-host=50.250.26.106;
 posting-account=3pYsyQoAAACcI-ym7XtMOI2PDU8gRZS5
NNTP-Posting-Host: 50.250.26.106
User-Agent: G2/1.0
MIME-Version: 1.0
Message-ID: <60637c3a-c699-4e4c-9fd3-1a081cb6152c@googlegroups.com>
Subject: Select + Accept syntax question
From: Andrew Shvets <andrew.shvets@gmail.com>
Injection-Date: Sat, 27 Aug 2016 18:26:03 +0000
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Xref: news.eternal-september.org comp.lang.ada:31605
Date: 2016-08-27T11:26:02-07:00
List-Id: <comp.lang.ada>

Hello,

When working with tasks, you can use a selective wait in order to have your=
 task quickly check its queue of messages and see if there any waiting for =
it (i.e. a selective wait.)  Now, in order to further build on this, guards=
 can be used to ensure that certain conditions are met before processing so=
me messages.

After messing around with both concepts, I created the following example:
while Go_Loop LOOP
  select
    when Internal_Value =3D 0 =3D>
      accept Input(Value : in Integer) do
        Internal_Value :=3D Value;
      end Input;
  or
    when Internal_Value /=3D 0 =3D>
      accept Retrieve(Value : out Integer) do
        Value :=3D Internal_Value;
      end Retrieve;

The one thing that threw me for a loop was when I put any type of code righ=
t before the above two accept keywords, like so:
while Go_Loop LOOP
  select
    when Internal_Value =3D 0 =3D>
      Ada.Text_IO.Put_Line("hello world");
      accept Input(Value : in Integer) do
        Internal_Value :=3D Value;
      end Input;
  or
    when Internal_Value /=3D 0 =3D>
      Ada.Text_IO.Put_Line("hello world");
      accept Retrieve(Value : out Integer) do
        Value :=3D Internal_Value;
      end Retrieve;

And I get the following output from the compiler:

> gnatmake -g .\task_demo_11.adb
gcc -c -I.\ -g -I- .\task_demo_11.adb
task_demo_11.adb:25:16: missing "END SELECT;" for "SELECT" at line 18
task_demo_11.adb:25:17: select alternative ("ACCEPT", "ABORT", "DELAY") exp=
ected
task_demo_11.adb:38:07: "OR" not allowed here
task_demo_11.adb:42:07: no "SELECT" for this "END SELECT"
gnatmake: ".\task_demo_11.adb" compilation error

Why does this happen?  Why can't I have code right before the accept?  I ca=
n see a compilation error if there is no accept...