RE: Evaluate complex conditions

[Buck Calabro <buck.calabro@xxxxxxxxxxxxxxxxx>]

Terry Grider wrote:

>Has anyone ever written or seen an 
>example of program code designed to
>evaluate complex conditions?  For 
>example, if you wanted to evaluate 
>a =b and (c = d or c = e or c = f).  
>I'm looking for something that can do
>multiple levels of parenthesis and 
>all "and/or" combinations.

I had to do this years and years ago on S/3 using RPG II.  The book I used
(and still keep on my shelf here at work) is "Compiler Design Theory" by
Lewis, Rosenkrantz and Stearns.  Addison-Wesley Publishing Co., Nov. 1978.
It's part of the IBM Systems Programming Series.  

I'm not going to pretend to have workable code for you using RPG, but you
can use ReXX to do much of the work for you:  Here is a ReXX example.  Place
this in QREXSRC, member EVAL.  To execute, strrexprc eval.

/* EVAL - Evaluate expressions */                                           
/* The goofy variable names are there to avoid conflicts with user input */ 
                                                                            
Top:                                                                        
   Signal On Syntax                                                         
   Do i0z0=1                                                                
      last=c000                                                             
      Parse Pull c0z0                                                       
      Select                                                                
         When c0z0=''                                                       
            Then Say 'EXIT to quit.'                                        
         Otherwise                                                          
            Interpret c0z0                                                  
      End                                                                   
   End                                                                      
                                                                            
Syntax:                                                                     
   Say 'Error (rc =' rc':' errortext(rc)')'                                 
   Signal Top                                                               

I hope this helps.  It was the best I could do without knowing how you get
the expression and how you intend to use the results.

Buck Calabro
Aptis; Albany, NY
"We are what we repeatedly do.
 Excellence, then, is not an act, but a habit." --Aristotle


Billing Concepts Corp., a NASDAQ Listed Company, Symbol: BILL
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