Fabian,

I put together some code for an advanced Wiki search engine. I allowed algebraic entry of the expression and that gets converted to RPN to ease the evaluation or the expression. You can get the VFP code from here:

http://fox.wikis.com/wc.dll?Wiki~WikiAdvancedSearch

The code only handle logical operators and or not ( ). You should be able to alter it to handle + - / and *.

>I have to develope an interfase (a form) to allow this type of formula entry for calculation... I use reverse polish in HP but never thought in develope it!!!
>
>does anyone ever did something like this?
>or has a doc about the algorithm and considerations?