With point positioned inside a function call (currently with some restrictions, such as not within a string literal argument to it, and not within an inner call in creating the argument list), versor-languide-create-function-for-call (normally bound to C-insert e) creates an empty function definition to suit that call, just before the current function definition.
This lets you type a call to a function that doesn't yet exist, and then go and create the function without having to do all of the completely predictable manual text entry or pasting for it.