gemacs

An Emacs-like text editor written in Gerbil Scheme with dual backends — a terminal UI (TUI) using Scintilla and termbox, and a native GUI using Qt6. Over 1,000 registered commands covering the breadth of GNU Emacs functionality.

Features

• 1,001 commands — navigation, editing, search, buffers, windows, files, version control, programming, org-mode, shells, and more
• Dual backends — run in the terminal (gemacs) or as a native Qt desktop application (gemacs-qt)
• Gerbil syntax highlighting — built-in lexer-based highlighting for Gerbil Scheme source files
• Embedded shells — eshell (built-in Gerbil shell), external $SHELL subprocess, and Gerbil REPL (gxi)
• Emacs keybindings — familiar C-x, C-c, M-x prefix sequences with a hash-table keymap state machine
• Scintilla text engine — undo/redo history, reference-counted document pointers, folding, and multi-cursor support
• Kill ring, registers, bookmarks, marks — standard Emacs text management
• Macro recording — C-x ( / C-x ) / C-x e keyboard macros
• Window management — splitting, resizing, balancing, tab-bar, winner-mode
• In-process eval — M-: evaluates Gerbil expressions from the echo area

Dependencies

• Gerbil Scheme (v0.19+)
• gerbil-scintilla — Scintilla + termbox FFI bindings (required for TUI backend)
• gerbil-qt — Qt6 FFI bindings (optional, for Qt backend)

Build

# Build gerbil-scintilla first (required)
cd ~/mine/gerbil-scintilla && make build

# Optionally build gerbil-qt for the Qt backend
cd ~/mine/gerbil-qt && make build

# Build gemacs (both TUI and Qt executables)
cd ~/mine/gemacs
make          # compile all modules + executables
make test     # run unit tests (55+ checks, 30+ test cases)
make install  # install binaries to ~/.local/bin/

Override the install prefix:

make install PREFIX=/usr/local

Usage

# Terminal UI
gemacs                    # open with *scratch* buffer
gemacs file1.txt file2.ss # open files

# Qt GUI
gemacs-qt                 # open with *scratch* buffer
gemacs-qt file1.txt       # open files

Key Bindings

Navigation

Key	Command	Description
C-f / Right	forward-char	Move forward one character
C-b / Left	backward-char	Move backward one character
C-n / Down	next-line	Move to next line
C-p / Up	previous-line	Move to previous line
C-a / Home	beginning-of-line	Move to beginning of line
C-e / End	end-of-line	Move to end of line
M-f	forward-word	Move forward one word
M-b	backward-word	Move backward one word
M-<	beginning-of-buffer	Move to beginning of buffer
M->	end-of-buffer	Move to end of buffer
C-v / PgDn	scroll-down	Scroll down one page
M-v / PgUp	scroll-up	Scroll up one page
C-l	recenter	Recenter view on cursor
M-g g	goto-line	Go to a specific line number

Editing

Key	Command	Description
C-d / Delete	delete-char	Delete character at point
DEL / C-h	backward-delete-char	Delete character before point
C-k	kill-line	Kill from point to end of line
C-y	yank	Yank (paste) last killed text
M-y	yank-pop	Cycle through kill ring
C-w	kill-region	Kill region (mark to point)
M-w	copy-region	Copy region without killing
C-@	set-mark	Set mark at point
C-_	undo	Undo last change
C-x u	redo	Redo last undone change
C-o	open-line	Open a new line below
C-m / C-j	newline	Insert newline
M-q	fill-paragraph	Reflow paragraph
M-;	comment-dwim	Toggle comment on region/line
C-t	transpose-chars	Transpose characters
M-t	transpose-words	Transpose words
M-u	upcase-word	Uppercase word
M-l	downcase-word	Lowercase word
M-c	capitalize-word	Capitalize word

Search and Replace

Key	Command	Description
C-s	search-forward	Incremental search forward
C-r	search-backward	Incremental search backward
M-%	query-replace	Interactive search and replace
M-x occur	occur	List matching lines

Files and Buffers

Key	Command	Description
C-x C-f	find-file	Open a file
C-x C-s	save-buffer	Save current buffer
C-x C-w	write-file	Save buffer to a new file
C-x b	switch-buffer	Switch to a buffer by name
C-x k	kill-buffer	Kill current buffer
C-x C-b	buffer-list	List all buffers
C-x d	dired	Directory editor

Windows

Key	Command	Description
C-x 2	split-window	Split window vertically
C-x 3	split-window-right	Split window horizontally
C-x o	other-window	Switch to other window
C-x 0	delete-window	Delete current window
C-x 1	delete-other-windows	Delete all other windows
C-x +	balance-windows	Balance window sizes

Help

Key	Command	Description
C-h k	describe-key	Describe what a key does
C-h f	describe-function	Describe a command
C-h b	describe-bindings	List all key bindings
C-h a	apropos-command	Search commands by name
C-h w	where-is	Find key binding for a command

Shells and REPL

Key	Command	Description
C-x r	repl	Open Gerbil REPL (gxi subprocess)
M-x eshell	eshell	Open built-in Gerbil shell
M-x shell	shell	Open external $SHELL subprocess
M-:	eval-expression	Evaluate Gerbil expression in echo area

Bookmarks and Registers

Key	Command	Description
C-x r m	bookmark-set	Set a bookmark
C-x r b	bookmark-jump	Jump to a bookmark
C-x r s	copy-to-register	Save region to register
C-x r i	insert-register	Insert register contents

Macros

Key	Command	Description
C-x (	start-kbd-macro	Start recording a macro
C-x )	end-kbd-macro	Stop recording
C-x e	call-last-kbd-macro	Execute last macro

Other

Key	Command	Description
M-x	execute-extended-command	Run a command by name
C-g	keyboard-quit	Cancel current operation
C-x C-c	quit	Exit the editor

Command Categories

The 1,001 commands span these areas:

Category	Examples
Core editing	kill/yank, undo/redo, transpose, case conversion, fill, indent
Navigation	goto-line, imenu, avy, bookmarks, mark ring, sexp movement
Search	isearch, query-replace, occur, grep, rg, deadgrep
Buffers & Windows	split, resize, balance, tab-bar, winner, ibuffer, windmove
File management	find-file, save, revert, dired, recent files, auto-save
Programming	syntax highlighting, paren matching, compile, xref, LSP, DAP, flycheck
Language modes	Gerbil, Scheme, Emacs Lisp, Python, Ruby, JavaScript, TypeScript, Go, Rust, C/C++, Java, Haskell, OCaml
Version control	magit (status, log, commit, diff, blame, stash, fetch, push, pull, rebase, merge), git-gutter
Text processing	sort, align, rectangles, string inflection, multiple cursors, paredit, smartparens
Org-mode	headings, TODO cycling, scheduling, agenda, export, babel
Shell & REPL	eshell (built-in), shell (external), Gerbil REPL (gxi), eval-expression
Modern packages	consult, embark, corfu, cape, vertico, marginalia, orderless, which-key
Writing	olivetti, writeroom, focus-mode, spell checking (jinx, flyspell)
Utilities	calc, calendar, EWW browser, EMMS media, PDF tools, markdown, snippets, ediff
Appearance	themes, rainbow delimiters, hl-todo, indent guides, minimap, doom-modeline
Modal editing	evil-mode, meow-mode stubs

Architecture

gemacs/
  core.ss           Shared state, buffer predicates, eval helpers, default keybindings
  keymap.ss         Key event translation and keymap state machine
  buffer.ss         Buffer management with Scintilla document pointers
  window.ss         Frame and window layout (splitting, resizing)
  modeline.ss       Status line rendering (file, line/col, modified, mode)
  echo.ss           Echo area / minibuffer (messages and blocking prompts)
  highlight.ss      Gerbil syntax highlighting via Scintilla lexers
  editor.ss         527 editor commands + command registry
  editor-extra.ss   474 additional commands (overflow module)
  app.ss            Main event loop, rendering, event dispatch
  main.ss           TUI executable entry point
  repl.ss           Gerbil REPL subprocess management (gxi)
  eshell.ss         Built-in Gerbil shell (pwd, cd, ls, echo, eval, which)
  shell.ss          External $SHELL subprocess terminal
  emacs-test.ss     Unit tests (55+ checks, 30+ test cases)

  qt/
    keymap.ss       Qt key event translation
    buffer.ss       Qt buffer management
    window.ss       Qt window/frame layout
    modeline.ss     Qt status line
    echo.ss         Qt echo area
    commands.ss     Qt editor commands
    app.ss          Qt main event loop
    main.ss         Qt executable entry point

Module Details

core.ss — Backend-agnostic shared state: buffer predicates (repl-buffer?, eshell-buffer?, shell-buffer?), eval-expression-string for in-process Gerbil eval, and default keybinding setup for both backends.

keymap.ss — Translates terminal/Qt key events into Emacs-style key strings (C-x, M-f, <up>, etc.) and implements a state machine for multi-key prefix sequences. Keymaps are hash tables mapping key strings to command symbols or nested sub-keymaps.

buffer.ss — Each buffer owns a reference-counted Scintilla document pointer. Switching buffers calls SCI_SETDOCPOINTER on the editor widget, preserving per-document undo history, cursor position, and content. Tracks file path, modified state, and lexer language.

window.ss — Manages a frame containing one or more vertically-stacked edit windows. Each window owns a Scintilla editor instance. Supports splitting, deletion, resizing, and balancing.

modeline.ss — Draws the status line at the bottom of each window: -UU-:**- buffer-name (line,col) Mode with reversed colors for the active window.

echo.ss — The bottom row of the terminal. Displays messages, errors (in red), and handles blocking text input with prompt display for commands like find-file and switch-buffer.

editor.ss + editor-extra.ss — Define all 1,001 editor commands and the app-state struct that ties everything together. Commands are stored in a registry and dispatched by symbol name from the keymap. The split into two files is for build performance.

app.ss — Initialization (terminal setup, keybindings, command registration, buffer creation) and the main event loop: process notifications, refresh windows, draw modelines and echo area, present to terminal, poll for input, dispatch events, poll REPL/shell output.

repl.ss — Manages gxi subprocesses for the embedded Gerbil REPL. Handles process lifecycle (start/send/read/stop) and non-blocking output polling integrated into the event loop.

eshell.ss — A built-in shell implemented entirely in Gerbil. Supports pwd, cd, ls, echo, which, eval, clear, exit, and falls through to external commands via open-process.

shell.ss — Spawns an external $SHELL process with pseudo-terminal emulation, ANSI code stripping, and bidirectional I/O integrated into the event loop.

How It Works

The editor uses Scintilla as its text engine and termbox (bundled inside gerbil-scintilla) for terminal I/O. The event loop:

1. Processes Scintilla notifications
2. Polls REPL, shell, and eshell buffers for subprocess output
3. Refreshes all editor windows
4. Draws modelines and echo area
5. Presents to terminal via tui-present!
6. Positions the cursor at the caret
7. Polls for input with a 50ms timeout
8. Dispatches key/mouse/resize events through the keymap state machine

Printable characters with no modifier are self-inserted. Unbound key sequences display an error in the echo area. M-x opens a command prompt for executing any of the 1,001 registered commands by name.

The Qt backend follows the same architecture but uses Qt widgets for rendering and Qt's event system for input handling, producing a native desktop application with the same command set.

License

MIT