The function gc() invokes the garbage collector. Normally, the collector runs automatically when available memory runs low, so you don't normally need to call it explicitly. However, in some situations, it is useful to be able to force a collect to ensure a pause due to garbage collection will be delayed as long as possible.
You can also invoke the collector to cause any unreferenced open files to be closed. In some situations, a file can be left open if a runtime error occurs while it is still open. If the file object was being held in a local variable at this point, it may not be possible to get at it from the Listener to force a close. Any subsequent attempts to open it may result in an "already open" error from the operating system. Running the collector will cause the file object to be reclaimed and this forces any open file associated with it to be closed.
This function returns the number of bytes free in the MAXScript heap after collection. Note that the collector may take many seconds to run if the heap is full of many small reclaimable objects.