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From: dewar@cs.nyu.edu (Robert Dewar)
Subject: Re: Please help a beginner! (second try)
Date: 1996/02/18
Message-ID: <dewar.824648920@schonberg>#1/1
X-Deja-AN: 139903316
references: <4g517q$438@helios.herts.ac.uk> <4g675n$dm4@news.pacifier.com>
organization: Courant Institute of Mathematical Sciences
newsgroups: comp.lang.ada
Date: 1996-02-18T00:00:00+00:00
List-Id: <comp.lang.ada>

Steve said

"Well, in Ada the main program is a procedure:

 PROCEDURE Main IS
 
 BEGIN
 END Main;
 
Careful Steve, this is wrong, you cannot have compiled it, you meant

 procedure Main is
 begin
    null;
 end Main;
Also, Steve's final solution for the procedure:

  with TEXT_IO;
  
  procedure main is
  
  package INT_IO is new TEXT_IO.INTEGER_IO(INTEGER);
  
  procedure proc1 is
  begin
    TEXT_IO.PUT("Hello");
    INT_IO.PUT(2);
  end proc1;
  
  begin
    TEXT_IO.PUT("Hello");
    INT_IO.PUT(2);
  end main;

is very confused, it seems to be the result of random code rearrangement
until something "works". In the above, which is not properly indented,
no doubt adding to the confusion, you have an internal procedure proc1
which is never called. A corrected version of the above is:

  with Ada.Text_IO;
  procedure Main is
  
    package Int_IO is new Ada.Text_IO.Integer_IO (Integer);
  
  begin
    Ada.Text_IO.Put ("Hello");
    Int_IO.Put (2);
  end Main;

However, I prefer not to teach generic instantiation so early (I would
bet for example that Steve does not 100% understand what he wrote there :-)
Instead in Ada 95, I would teach:

  with Ada.Text_IO;
  with Ada.Integer_Text_IO;
  
  procedure Main is
  begin
    Ada.Text_IO.Put ("Hello");
    Ada.Integer_Text_IO.Put (2);
  end Main;

Of course this only works with the built-in type Integer, but one of the
few legitimate uses of the built-in types is in teaching right at the
beginning. I also changed the casing to be more "standard". The use of
all upper case identifiers is now largely out of favor, so you might as
well teach the above casing style from the start.

Another approach is to introduce the attribute functions early on:

  with Ada.Text_IO;
  procedure Main is
  begin
    Ada.Text_IO.Put ("Hello");
    Ada.Text_IO.Put (Integer'Image (2));
  end Main;

One general comment is that if you are trying to understand Ada, or any
other language, at an elementary level like this, get a book and read it!
Using a newsgroup to try to learn at this level is a dicey proposition,
because sure there are people who can answer correctly, but the information
you get posted on any newsgroup is quite unreliable. On CLA for instance,
while it is better than some other newsgroups, people routinely through
accident or ignorance post as gospel statements about Ada that are
completely wrong, and if you don't know a fair amount to start with,
you can easily get confused.

To those who post suggested solutions to anything, a plea: PLEASE be sure
to compile and test your solution. Even if you know Ada well, it is good
insurance against a simple slip-up which can cause great confusion. For
example, I compiled and ran all three examples above, they are very simple,
and did indeed run error-free with no surprises, but no one can be 100%
sure of not making silly mistakes :-)