excel experts required

I am after some information about whether a particular Excel function exists or not...

As we all know, to enter a fuinction in excel, you put an equals sign, followed by the relevant formula into the cell, and it evaluates the function.

What I want to do is construct the actual character string for the formula (minus the equals sign) into a given cell, and then have the magic function evaluate it and put the result in another cell.

For example, assume I put the character string "B1+B2" in cell A1. I then use the magic function (let's call it "evaluate" as follows:

In cell A2 I enter =evaluate(A1) and it effectively returns the value that you would get if you entered =B1+B2 in the cell.

The purpose of this is to allow me to dynamically construct formulas based on the values of data in cells.

Does anyone know what function I should be using?

Thanks in advance, and keep those HDR shares moving ever upwards.