x
x
x


Do so in a way which:

 does not involve string manipulation of the input source code
 is plausibly extensible to a runtime-chosen set of bindings rather than just x
 does not make x a global variable


or note that these are impossible.



See also

 For more general examples and language-specific details, see Eval.
 Dynamic variable names is a similar task.


 
 
 expression$ = "x^2 - 7"
Print (EvaluateWithX(expression$, 5) - EvaluateWithX(expression$, 3))
End
 
Function EvaluateWithX(expression$, x)
    EvaluateWithX = Eval(expression$)
End Function 