Speeding up parsed equations

Hi, I have a problem with the speed of parsed equations. I want the user to be able to define a equation X.


Lets say they define it as X=y+1

then I execute

Code:

---

while (i < MAX)
{

value=value+(X)

}

---

Since it's user defined I call a parser to intepret the equation and return the value.
Unfortunately since it's calculated a million times everything gets seriously bogged down reparsing it every cycle. Is there a way to get it up to at least close to the speeds it would be if X was hardcoded? I've gotten suggestions like gnu lightning and writing my own virtual machine but they all are extremely complex, using often underdeveloped resources and often require the use of assembly. And I'm pretty much still a novice.

Do you call the parser every time through the loop?

Could you store the result of the parse (maybe using an expression tree) each time instead?

i did something like that with PHP.

i had the user declare what the variables were, enter the equation, and then i parsed the input, editing the string to make it compile, and then i used the php command line interface to run the code and i got the result from stdin.

it was pretty simple to implement and it was reasonably fast.

i'm sure you could build some kind of shell script and accomplish the same thing.

Feh. A Real Programmer would write code to translate the equation to C code, write it to a file, call the compiler on it, turn it into a DLL, then dynamically load it.

;)