Re: Suggestion for multivalue boolean case for 9X

[dale.cts.com!jhb@nosc.mil (John Bollenbacher)]

Mark Dunbar (dunbar@saifr00.cfsat.honeywell.com) wrote:
: In article <dnsurber.724028252@node_26400> dnsurber@lescsse.jsc.nasa.gov (Dou
glas N. Surber) writes:
: >How many times have you seen code like the following:
: >
: >    if cond_1 then
: >        if cond_2
: >	    if cond_3 then
: >		s_t_t_t;
: >	    else
: >		s_t_t_f;
: >	    end if;
: >	else
: >	    if cond_3 then
: >		s_t_f_t;
: >	    else
: >		s_t_f_f;
: >	    end if;
: >	end if;
: 
:       [etc]...
: 
: >I find this hard to read and even harder to maintain.  Cond_3 appears
: >four times.  That's a maintenance nightmare.  A case statement that
: >worked on arrays of booleans would be a big improvement.  Something like
: >the following:
: >
: >    case (cond_1, cond_2, cond_3) is
: >	when (true,  true,  true ) =>
: >	    s_t_t_t;
: >	when (true,  true,  false) =>
: >	    s_t_t_f;
: >	when (true,  false, true ) =>
: >	    s_t_f_t;
: >	when (true,  false, false) =>
: >	    s_t_f_f;
: 
: 	[etc]...
: >
: >Douglas Surber
: >Lockheed
: >Houston, TX
: >
: Using Ada83, instead of the nested if statement, one could do the following:
: 
:   if    ( not Cond_1 ) and ( not Cond_2 ) and ( not Cond_3 ) then
:     ...
:   elsif ( not Cond_1 ) and ( not Cond_2 ) and (     Cond_3 ) then
:     ...
:   elsif ( not Cond_1 ) and (     Cond_2 ) and ( not Cond_3 ) then
:     ...
:   elsif ( not Cond_1 ) and (     Cond_2 ) and (     Cond_3 ) then
:     ...
:   elsif (     Cond_1 ) and ( not Cond_2 ) and ( not Cond_3 ) then
:     ...
: 
:   etc.
: 
: Although I do agree the case statement would be more elegant (sp?) and
: potentially faster if there were enough branches to cancel out the
: overhead of a case.

Though I also agree that the original posting has merit, another possibility 
that I have used is something like:

  declare
    type BOOLS is array (1..3) of BOOLEAN;
    VAL : constant BOOLS := (COND_1, COND_2, COND_3);
  begin
    if VAL = (TRUE, TRUE, TRUE) then
      ...
    elsif VAL = (TRUE, TRUE, FALSE) then
      ...
    etc.
--
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- John Bollenbacher                                        jhb@dale.cts.com -
- Titan Linkabit Corp.                                       (619) 552-9963 -
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