In computer science, the funarg problem (function argument problem) refers to the difficulty in implementing first-class functions (functions as first-class objects) in programming language implementations so as to use stack-based memory allocation of the functions. The difficulty only arises if the body of a nested function refers directly (i.e., not by argument passing) to identifiers defined in the environment in which the function is defined, but not in the environment of the function call. A standard resolution is either to forbid such references or to create closures. There are two subtly different versions of the funarg problem. The upwards funarg problem arises from returning (or otherwise transmitting "upwards") a function from a function call. The downwards funarg problem arises from passing a function as a parameter to another function call. Upwards funarg problem When one function calls another during a typical program's execution, the local state of the caller (including parameters and local variables) must be preserved in order for execution to proceed after the callee returns. In most compiled programs, this local state is stored on the call stack in a data structure called a stack frame or activation record. This stack frame is pushed, or allocated, as prelude to calling another function, and is popped, or deallocated, when the other function returns to the function that did the call. The upwards funarg problem arises when the calling function refers to the called/exited function's state after that function has returned. Therefore, the stack frame containing the called function's state variables must not be deallocated when the function returns, violating the stack-based function call paradigm. One solution to the upwards funarg problem is to simply allocate all activation records from the heap instead of the stack and rely on some form of garbage collection or reference counting to deallocate them when they are no longer needed. Managing activation records on the heap has historically been perceived to be less efficient than on the stack (although this is partially contradicted) and has been perceived to impose significant implementation complexity. Most functions in typical programs (less so for programs in functional programming languages) do not create upwards funargs, adding to concerns about potential overhead associated with their implementation. Furthermore, this approach is genuinely difficult in languages that do not support garbage collection. Some efficiency-minded compilers employ a hybrid approach in which the activation records for a function are allocated from the stack