Depends on what you mean. If you just mean writing an implementation of Emacs (or something Emacs-like) in Common Lisp, that's not very hard, and it's been don

Depends on what you mean. If you just mean writing an implementation of Emacs (or something Emacs-like) in Common Lisp, that's not very hard, and it's been done a few times. See, for example, Lem[1] and Hemlock[2]. Heck, I wrote one for MacOSX in about 2001 or 2002. If you mean a drop-in replacement for GNU Emacs, that's a lot harder. Besides the UI and the editing infrastructure, you need to write a bug-compatible implementation of GNU's elisp, or you lose the whole GNU Emacs ecosystem. That ecosystem is most of its practical appeal. That's a whole bunch of work. [1] https://github.com/40ants/lem-pareto/blob/master/lem-pareto-mode.lisp https://github.com/40ants/lem-pareto/blob/master/lem-pareto-... [2] https://en.wikipedia.org/wiki/Hemlock_(text_editor) https://en.wikipedia.org/wiki/Hemlock_(text_editor)