Lethe Text Editor#

A minimal vi-like text editor written in Zig 0.15.

Lethe is a single-file terminal editor with a familiar modal interface. It was built from scratch with no dependencies beyond the Zig standard library — no curses, no terminfo, just raw ANSI escape sequences.

The name comes from the river of forgetfulness in Greek mythology. Your original file is never touched — Lethe always writes new versions alongside it.

Features#

• Vi-style modal editing — Normal and Insert modes with the keybindings you’d expect
• Word-wrap display — Long lines wrap at word boundaries (spaces, hyphens), not mid-word
• Line numbers — Dimmed gutter with right-aligned numbers; continuation lines show blank gutters so you always know what’s a real line vs. a soft wrap
• VMS-style file versioning — Saves go to file.txt.1, file.txt.2, etc. The original is never overwritten. Highest number = newest version
• Undo — Snapshot-based with vi semantics: one undo per edit action, not per keystroke
• Built-in help — Press ? to toggle a quick-reference overlay
• I18n-ready — All UI strings are constants at the top of the file

Building#

zig build-exe src/main.zig -o lethe

Or with a build.zig:

zig build

Requires Zig 0.15.2 or compatible. Linux only (uses ioctl for terminal size and POSIX termios for raw mode).

To enable the squash command, create a symlink:

ln -s lethe squash

Usage#

./lethe myfile.txt

Keybindings#

Normal Mode#

Insert Mode#

File Versioning#

Lethe never modifies your original file. When you press w:

myfile.txt      ← original, untouched
myfile.txt.1    ← first save
myfile.txt.2    ← second save
myfile.txt.3    ← third save (newest)

The status bar confirms which version was written.

Squash#

Over time, versions accumulate. To consolidate, use the squash command — the same binary, invoked via symlink:

ln -s lethe squash

./squash myfile.txt
# myfile.txt.3 -> myfile.txt (2 version(s) removed)

This finds the highest-numbered version, deletes everything else (including the original), and renames the newest version to the original filename. One command, clean slate.

Architecture#

The entire editor is a single Zig source file (~820 lines). Key design decisions:

• ArenaAllocator — All memory is arena-allocated. Nothing is individually freed until the editor exits. This keeps the code simple and makes undo snapshots essentially free.
• Raw terminal mode — POSIX termios with ICANON, ECHO, ISIG disabled. Alternate screen buffer so your terminal is restored on exit.
• Buffered I/O — Uses Zig 0.15’s new std.Io.Writer interface with a 4K buffer. One flush per render cycle.
• Word-wrap — wrapPositions() scans for spaces and hyphens to find natural break points. Falls back to hard wrap for long unbroken strings (URLs, etc.).
• Operator-pending state — For compound commands like dd, d$, cw. A single pending_op byte remembers the first keystroke.
• Multi-personality binary — The same binary acts as editor or version squasher depending on argv[0]. A symlink is all it takes.

Limitations#

• No syntax highlighting
• No search (/)
• No yank/paste (y/p)
• No multi-file editing
• No redo (only undo)
• Linux only (POSIX termios + Linux ioctl)
• Maximum ~256 visual wrap lines per source line

Localization#

All user-facing strings live in the strings struct at the top of the file. To translate the UI, just change those constants:

const strings = struct {
    const mode_normal = "NORMAL";
    const mode_insert = "INSERT";
    const label_line = "Line";
    const label_col = "Col";
    // ...
};

License#

GNU GPLv3