1. A computer-based method of accessing a closure variable defined in a function of a computer program from a lambda expression that is invoked from a computer program location outside the function while an instance of the function is active, the closure variable stored in a frame on a runtime stack, the frame corresponding to the function instance, comprising: a) in response to entering the function during program execution, storing a pointer to the closure variable in a data structure; b) in response to an instruction to retrieve a value of the closure variable, the instruction in the lambda expression, employing the pointer to locate the closure variable in the frame on the runtime stack and retrieve the variable value: c) automatically inserting a closure creation instruction to create a closure object in response to an invocation of the function; and d) automatically inserting a variable reference instruction to retrieve the closure variable value from within the lambda expression.