Invar — a terminal code editor

Desktop-editor ergonomics, in the terminal. Invar is a fast, mouse- and keyboard-driven code workspace that runs entirely in your terminal — a file tree, a real text editor with word wrap and wide/emoji-aware columns, fuzzy go-to-file, find & replace, a git panel with side-by-side diffs and staging, a command palette, settings, and tabs. Built on Bun + ivue + OpenTUI + Tree-sitter + git.

The design goal: a newcomer can learn it in ~15 minutes — every action has a visible, clickable affordance, and no capability requires a memorized motion.

Why "Invar"? Invar is the iron–nickel alloy discovered by Charles Édouard Guillaume in 1896 — named from invariable, because its thermal expansion is near zero. Precision clocks and measuring instruments were built from it for one reason: it does not drift. This editor is built the same way — every module carries an explicit invariants contract, and a merge gate keeps the structure from drifting, no matter how much heat the codebase takes. (Guillaume got the 1920 Nobel Prize in Physics for the alloy. We just got an editor.)

And the binary is iv — which is vi, reversed. On purpose. Same terminal, opposite philosophy: nothing to memorize, everything visible.

Quickstart

bun install
bun run start          # open the current directory as the workspace
bun run dev <dir>      # open a specific directory

Quit with Ctrl+Q or F10. Command palette is F1; fuzzy go-to-file is Ctrl+P. Full run/build/test instructions live in project.build.md.

Build a standalone binary:

bun run build          # → dist/iv  (self-contained executable)
./dist/iv .

Built with Invariant-Based Reasoning (IBR)

This editor is also a demonstration of IBR — a method that reduces a problem to the irreducible structures that actually exist in its domain, then generates from them. Every module carries a colocated *.invariants.md contract; a hard merge gate verifies those invariants by driving the real user path (injecting input, reading the rendered framebuffer) rather than trusting internal values — and blocks any commit that regresses them. Capabilities live behind a replaceable Static() seam, enforced by an AST gate, so the whole system stays extensible.

The framework itself is here, free to use and build on:

• .claude/skills/ibr/IBR.md — the IBR framework
• .claude/skills/invariants/ — the /invariants skill (contract schema + checker)

License

MIT — see LICENSE. Use it, learn from it, build on it.