Load dynamic delegate function from text file?

Question

I wana write dynamic delegate function, look like this

public delegate int functionX(int a, int b);
functionX = loadFunction(textFile); // the loadFunction is function i wana write.

So i wana change text file dynamic to have dynamic delegate function. Ex: text file like this, i will have functionX like Add function.

int Add(int a, int b)
{
    return a + b;
}

Or have functionX like Subtract function and ect...

int Subtract(int a, int b)
{
    return a - b;
}