RE: Dynamic formulae calculation in RPG

["Wilt, Charles" <WiltC@xxxxxxxxxx>]

Glenn,

I believe you misunderstood the original poster.

I believe what Ewart want's is a way to store the following formulas in a DB 
table:
Description             Name                    Formula                 
-------------------     -------         ----------------                
Base value              Base                    Qty * price                     
Tax1 20% of base        Tax1                    Base * .02                      
Tax2 30% of Tax1        Tax2                    Tax1 * .03              
Total                   Total                   Base + Tax1 + Tax2

The for instance, in his customer record, there would be a field perhaps called 
TAXCALC, that for a
given customer(s) would store the value "Total".

Now when figuring the tax for the given customer, his RPG program would need to 
dynamically figure out
that:

Customer's tax = Total
               = (Base + Tax1 + Tax2)
               = ((Qty * Price) + (base * .20) + (Tax1 * .30))
               = ((10 * 100) + ((10 * 100) * .20) + (((10 * 100) * .20) * .30))
               = 1260

(note corrected percentages 20% = .2 not .02)

I assume that the OP's example is considerably simplified and that there are 
reasons he couldn't just
store a tax rate of 26%

All that being the case, my answer to Ewart is as follows:
As far as I know, RPG doesn't have the built in dynamic capabilities you are 
looking for.  Basically,
to take a string such as '(10 * 100)' and evaluate it to the numeric value of 
1000.  

There's two steps to this problem as I see it:
1) Going from 'Total' to '((10 * 100) + ((10 * 100) * .20) + (((10 * 100) * 
.20) * .30))'
2) Evaluating '((10 * 100) + ((10 * 100) * .20) + (((10 * 100) * .20) * .30))'

Step one involves basically parsing a string till you get to all numeric or 
mathematical operation
characters.  This could be done recursively, in RPG IV or some other language.

For step two, you could technically write an RPG procedure or two that would 
calculate it.  Look
around on the net for examples of writing programs that process "infix" 
expressions.  Note that
writing this expression evaluator yourself would be considerably simplified if 
you used "postfix"
expressions, '10 10 *' instead of "infix" '10 * 10' (Google for infix and 
postfix for more info) 

However, it may be easier to just use a language that has the dynamic 
evaluation capabilities you
need.  Dynamic SQL would be one option.  The other option would be a language 
like Perl that includes
the dynamic evaluation you are looking for.

You might want to look at doing the whole calculation procedure in Perl or 
perhaps Rexx has the
capabilities you need.

HTH,

Charles Wilt 
Software Engineer
CINTAS Corporation - IT 92B
513.701.1307
wiltc@xxxxxxxxxx


-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx] On 
Behalf Of Glenn
Gundermann
Sent: Wednesday, March 14, 2007 8:51 AM
To: RPG programming on the AS400 / iSeries
Subject: Re: Dynamic formulae calculation in RPG

Ewart,

You should keep it simple and easy to read, hence easy to modify and easy to 
debug by coding it
exactly how you have it written down in your
requirements:
/free
 Base = Qty * Price;
 Tax1 = Base * .02;
 Tax2 = Tax1 * .03;
 Total = Base + Tax1 + Tax2;
/end-free

You could of course make it impossible for the next programmer to understand 
what you are doing:
/free
 Total = Qty * Price * 1.0206;
/end-free

Glenn Gundermann
ggundermann@xxxxxx
(647) 272-3295


> Hello All,
>
> We have a complicated Invoice calculation process where a lot local 
> taxes are to be considered. In order to make these calculations 
> dynamic I plan to do the calculations using dynamic formulas so that 
> any future changes can be considered.
>
> Eg:
>
> Description             Name            Formula         Value
> Base value              Base            Qty * price             1000
> Tax1 20% of base        Tax1            Base * .02              20
> Tax2 30% of Tax1        Tax2            Tax1 * .03              0.6
> Total                   Total           Base + Tax1 + Tax2      1020.6
>
>
> Has anyone built something like that & can share the code - I can save 
> some time.
>
> Thanks & best regards
> Ewart
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