Providing for read/write access to captured free variables expressed as environment data objects is disclosed herein. By way of example, free variables can be rewritten as a field of a private class, and accessed via an instance of the private class captured within the environment data object. In such a manner, no need of a placeholder or proxy function is required to access the free variable. Consequently, the subject innovation provides a simplified method for capturing free variables within expression trees and providing read/write access to such variables.