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1 Introduction

Hemlock is a text editor which follows in the tradition of editors such as EMACS and the Lisp Machine editor ZWEI. In its basic form, Hemlock has almost the same command set as EMACS, and similar features such as multiple buffers and windows, extended commands, and built in documentation.

Both user extensions and the original commands are written in Lisp, therefore a command implementor will have a working knowledge of this language. Users not familiar with Lisp need not despair however. Many users of Multics EMACS, another text editor written in Lisp, came to learn Lisp simply for the purpose of writing their own editor extensions, and found, to their surprise, that it was really pretty easy to write simple commands.

This document describes the Common Lisp functions, macros and data structures that are used to implement new commands. The basic editor consists of a set of Lisp utility functions for manipulating buffers and the other data structures of the editor as well as handling the display. All user level commands are written in terms of these functions. To find out how to define commands see chapter commands.