An editor for revision control

Programming environments support revision control in several guises. Explicitly, revision control software manages the trees of revisions that grow as software is modified. Implicitly, editors retain past versions by automatically saving backup copies and by allowing users to undo commands. This paper describes an editor that offers a uniform solution to these problems by never destroying the old version of the file being edited. It represents files using a generalization of AVL trees called “AVL dags,” which makes it affordable to automatically retain past versions of files. Automatic retention makes revision maintenance transparent to users. The editor also uses the same command language to edit both text and revision trees.