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From: Richard D Riehle <laoXhai@ix.netcom.com>
Subject: Re: Expressive Case Statements (was: Software landmines)
Date: 1998/09/02
Message-ID: <6si98q$fbo@sjx-ixn4.ix.netcom.com>#1/1
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 <EACHUS.98Sep1193718@spectre.mitre.org>
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X-NETCOM-Date: Tue Sep 01  7:07:22 PM PDT 1998
Newsgroups: comp.lang.ada
Date: 1998-09-01T19:07:22-07:00
List-Id: <comp.lang.ada>

In article <EACHUS.98Sep1193718@spectre.mitre.org>,
	eachus@spectre.mitre.org (Robert I. Eachus) wrote:

  as a solution to the problem I posed about truth tables,

>     type Truth_Table_3 is (False_False_False, False_False_True,...
>                                 True_True_True); 
>     function To_TT3(Cond_1,Cond_2,Cond_3 : Boolean := False)
>                                            return Truth_Table_3;
>
>     case To_TT3(Condition_1, Condition_2, Condition_3) is
>       when True_True_False  => some_action_stub_statements;
>       when True_False_False => some_action_stub statements2;
>       when False_False_True => some_action_stub statements3;
>       when others => null;
>     end case;

  This comes close to what I am seeking.  Now I need to read it over
  and see it I can make it more general.  

  Thanks for your ideas, Robert.  

>     Obviously you want the various truth table types in a package,
>and you have several ways of writing the bodies of the conversion
>functions.  I prefer:
>
>     function To_TT3(Cond_1,Cond_2,Cond_3 : Boolean := False) 
>                                        return Truth_Table_3 is
>     begin
>       return Truth_Table_3'Val(Cond_1'Pos * 4 + Cond_2'Pos * 2 + Cond_3);
>     end To_TT3;
>
> I think I'd write a program to crank out the type declarations
> though.

  I need to code this as a compilable example and see if I can 
  generalize it.  As it is, it appears to satisfy the special 
  case of a three-valued table. 
 
  The example coded in a functional language looked very good, but
  that is not Ada.  

  Thanks again.

  Richard