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Date: Thu, 29 Oct 2015 21:53:20 -0700 (PDT)
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Subject: Help with constructing an Ada Shell
From: annihilan@gmail.com
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Xref: news.eternal-september.org comp.lang.ada:28120
Date: 2015-10-29T21:53:20-07:00
List-Id: <comp.lang.ada>

Okay. So I've been trying to learn Ada recently, which unfortunately means =
that my question isn't going to be very sophisticated. I have the following=
 code:

with Ada.Text_IO; use Ada.Text_IO;

with GNAT.OS_Lib; use GNAT.OS_Lib;
with GNAT.Strings;

package body Ada_Shell is
   Input : aliased String :=3D (1 .. 255 =3D> ' ');
   Last : Integer;
   procedure Main is
      package IO renames Ada.Text_IO;
   begin
      IO.Put_Line("Welcome to ash! This is an extreme work in progress.");
  Main_Loop:
      loop
	 Input :=3D (others=3D> ' ');
	 IO.Put("ash> ");
	 IO.Get_Line(Input, Last);
	 if Input(Input'First..Last) =3D "quit" then
	    exit Main_Loop;
	 else
	    Execute_System;
	 end if;
      end loop Main_Loop;
   end Main;
  =20
   procedure Execute_System is
      Result : Integer;
      Arguments : Argument_List :=3D
	(1 =3D> Input'Access);
   begin
      Spawn (Program_Name =3D> Input, -- truncate strings or Input(Input'Fi=
rst..Last)??
	     Args =3D> Arguments,
	     Output_File_Descriptor =3D> Standout,
	     Return_Code =3D> Result);
      --  for Index in Arguments'Range loop
      --  	 Free(Arguments(Index));
      --  end loop;
      Put_Line(Integer'Image(Result));
   end Execute_System;
end Ada_Shell;

This code is executed by a simple procedure that calls the Main loop of the=
 package. I don't know if there's a "better" way to make a repeating main l=
oop like this, but I couldn't contrive a better solution.=20
Besides, this code does not work. It compiles, sure, but it doesn't work. N=
o matter what command is passed at the prompt, a return value of 1 is given=
.=20

Things I have tried that work:
hardcoding the program at Spawn(Program_Name=3D>"/bin/ls") or similar

Things I have tried that have not worked:
Having Execute_System be in a separate file, and having its signature as Ex=
ecute_System(Command:access String) (this worked especially poorly, bringin=
g in aliasing problems that I couldn't solve.

I really don't know why this doesn't work. The reason that the result code =
and command line are global was to eliminate "non-local pointer references =
local object" and "implicit conversion of anonymous access formal" errors. =
I haven't tried uncommenting the Free block since I fixed everything, thoug=
h.

I would massively appreciate any help that could be given to me. I don't re=
ally have any clue at all what's going on.