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 = "return pow(x,2) - 7"
one = evalwithx(expression, 1.2)
two = evalwithx(expression, 3.4)
see "one = " + one + nl + "two = " + two + nl
 
func evalwithx expr, x
     return eval(expr)
 