99% of the time, you simply write the code or change in the sources first, then compile/run it in the runtime.
If you're modifying the runtime directly at the REPL without having sources, good luck? or you don't really care about persisting those changes. CL has pretty good introspection, so you could look at the source expression of a function defined at the REPL for example, if you really wanted to recover something (and happened to put the change in a function first), but this isn't always reliable.
99% of the time, you simply write the code or change in the sources first, then compile/run it in the runtime.
If you're modifying the runtime directly at the REPL without having sources, good luck? or you don't really care about persisting those changes. CL has pretty good introspection, so you could look at the source expression of a function defined at the REPL for example, if you really wanted to recover something (and happened to put the change in a function first), but this isn't always reliable.