Ada for Software Engineers

Errata for Ada for Software Engineers

I would like to thank the readers who noted the errors.

Page 184 program lines 26-28. The words within the strings should not be boldface.
(Jeanne Murtagh.)
Page 207 line 8. f(x) should be f(y). See:
James M. Ortega. An Introduction to Fortran 90 for Scientific Computing.
Saunders College Publishing, 1994, p. 72-74.
Page 286. Add
```
delay 0.0;
```
after line 25 of the program to ensure that there is a dispatching point that will allow task Periodic to be executed.
(Kris Hermans.)

Section 16.5. The example program dist.ada is not correct. The designated type of a remote access type must be limited private by E.2.2(9). If you make it limited private, then the RCI packages are not correct because they may not define a limited type by E.2.3(11). You need an extra level of indirection as shown in the following program.
This problem was not caught on version 3.10p of GNAT that I used.
(Jack Flynn.)

--
-- Distributed dispatching.
--
package Root_Event is
  pragma Remote_Types;
  type Event is abstract tagged limited private;
  type Event_Ptr is access all Event'Class;
  procedure Simulate(E: in Event) is abstract;
private
  type Event is abstract tagged limited null record;
end Root_Event;

with Root_Event;
package Simulation_Server is
  pragma Remote_Call_Interface;
  procedure Go_Simulate(E_Ptr: Root_Event.Event_Ptr);
end Simulation_Server;

package body Simulation_Server is
  procedure Go_Simulate(E_Ptr: Root_Event.Event_Ptr) is
  begin
    Root_Event.Simulate(E_Ptr.all);
  end Go_Simulate;
end Simulation_Server;

package Root_Event.Engine is
  type Engine_Event is new Event with private;
  function Create(F, O: Natural) return Event_Ptr;
  procedure Simulate(E: in Engine_Event);
private
  type Engine_Ptr is access all Engine_Event;
  type Engine_Event is new Event with
    record
      Fuel, Oxygen: Natural;
    end record;
end Root_Event.Engine;

with Ada.Text_IO; use Ada.Text_IO;
package body Root_Event.Engine is
  function Create(F, O: Natural) return Event_Ptr is
    E: Engine_Ptr := new Engine_Event;
  begin
    E.Fuel := F; E.Oxygen := O;
    return Event_Ptr(E);
  end Create;
  procedure Simulate(E: in Engine_Event) is
  begin
    Put_Line("Engine fuel " & Integer'Image(E.Fuel) &
             " L, oxygen " & Integer'Image(E.Oxygen) & " L");
  end Simulate;
end Root_Event.Engine;

package Root_Event.Telemetry is
  type Telemetry_Event is new Event with private;
  type Subsystems is (Engines, Guidance, Communications);
  type States is (OK, Failed);
  function Create(Sub: Subsystems; St: States) return Event_Ptr;
  procedure Simulate(E: in Telemetry_Event);
private
  type Telemetry_Ptr is access all Telemetry_Event;
  type Telemetry_Event is new Event with
    record
      ID:     Subsystems;
      Status: States;
    end record;
end Root_Event.Telemetry;

with Ada.Text_IO; use Ada.Text_IO;
package body Root_Event.Telemetry is
  function Create(Sub: Subsystems; St: States) return Event_Ptr is
    E: Telemetry_Ptr := new Telemetry_Event;
  begin
    E.ID := Sub; E.Status := St;
    return Event_Ptr(E);
  end Create;
  procedure Simulate(E: in Telemetry_Event) is
  begin 
    Put_Line("Telemetry message " & 
             Subsystems'Image(E.ID) & " " &
             States'Image(E.Status));
  end Simulate;
end Root_Event.Telemetry;

with Root_Event;
with Simulation_Server;
with Root_Event.Telemetry; with Root_Event.Engine;
with Ada.Text_IO; use Ada.Text_IO;
procedure Dist is
  function Get_Event return Root_Event.Event_Ptr is
    C: Character;
  begin
    Put(" Choose system "); Get(C);
    if C = 'e' then
      return Root_Event.Engine.Create(500, 600);
    else
      return Root_Event.Telemetry.Create(
               Root_Event.Telemetry.Engines,
               Root_Event.Telemetry.Failed);
    end if;
  end Get_Event;

begin
  Simulation_Server.Go_Simulate(Get_Event);
end Dist;