Import Doesn't Scale - Exec is a between-process method of code re-use. - Import is a within-process method of code re-use. - Import does not work between processes, except via `fork()`. - Because Concurrency Primitives are Broken, `fork()` often can't be mixed with threads. - The import method of sharing code does not work between languages, except via awkward foreign function interface APIs. - Unix got it right.