The ed function invokes the Hemlock editor which is described in ıHemlock User's Manual and ıHemlock Command Implementor's Manual. Most users at CMU prefer to use Hemlock's slave Common Lisp mechanism which provides an interactive buffer for the read-eval-print loop and editor commands for evaluating and compiling text from a buffer into the slave Common Lisp. Since the editor runs in the Common Lisp, using slaves keeps users from trashing their editor by developing in the same Common Lisp with Hemlock.