An excuse to buy new tools

And that's going to save you money? All those new tools....

Dear Len,
I want a little of you advice in a making of a computer program.
Actually i recently made a very simple software. It basically captures the "stock market" transactions. After capturing tractions, the decision of buying or selling is made according to some pre defined formulas. For example

1) If total shares purchased are greater than 50 and and stockmarket opening time is 9:30 AM then sell 23 shares.

2) If stock market opening time is greater than 9:30 then do not buy any share till 11:30 and after 11:30 use formula ABC to get share difference and if difference is negative than buy that share.

There are 11 such conditions defined by our client. We've hardcoded all these condiotions in our source code.

Now the problem is that, these conditions are hardcoded and client daily wants to change conditions or define new conditions. Whenever client wants to enter new condition, it call us, then we add such condition or formula in the source code and then send updated copy.

Now we want to make this generic i.e we want to add new feature so that our client can himself add new condition or change existing at runtime. This is where i require your advice. suppose if you were at my place that what had you done ? Does the solution lies in writing parser/compiler.