I like antirez's "Linenoise" library. I converted it to Unicode, and gave it a multi-line editing mode with undo, visual copy and paste, edit in external editor, parenthesis matching, incomplete syntax continuation, and more. It's all in the TXR Lisp REPL.
I've tried to keep it decoupled from TXR internals, and to abstract it from the OS a bit, so there is a considerable "struct lino_os" interface now.
There is a dependency on a "config.h" which provides some HAVE_* constants.
There is a user guide to the REPL in the TXR Lisp manual; that provides context for some of new interfaces, like what is the lino_set_atom_cb function for.
