Hello, I have a lambda expression that is suppoalways constructed as [some lambda expression] / ( _1 - c); where c is a double constant, for example c = 3.14. What I need is a function that given the expression returns the internal value of c, if that is possible: template<class LambdaExp> double c(LambdaExp expr){ ... return c in expr assuming that expr has the form [...]/(_1 - c) } The function may throw an exception or whatever if the expr is not of the form [...]/(_1 - c) Some additional infomation that maybe useful to simplify the solution: the lambda expression returns a double, _1 is meant to be a placeholder for double. optional feature: Also it would be ideal if the function could also recognize *simple* alternative expressions like [..]/(_1 + k) (and return -k) or [...]/( k + _1) (and return -k). Solutions using other lambda-like libraries are welcomed too. Thank you, Alfredo