Ewig Editor

Ewig - Eternal Didactic Text Editor

The eternal text editor — Didactic Ersatz Emacs demonstrating immutable data-structures and the single-atom architecture.

Repository

• Source: https://github.com/bmorphism/ewig (fork of arximboldi/ewig)
• Language: C++ (immer library)
• Pattern: Persistent data structures + single atom state

Core Concept

Ewig demonstrates how to build a text editor using:

1. Immutable data structures - All state changes create new versions
2. Single-atom architecture - One atom holds the entire application state
3. Structural sharing - Efficient memory via shared structure

// Single atom state
atom<editor_state> state;

// All mutations are pure transformations
state.update([](editor_state s) {
    return s.insert_char('x');  // Returns new state, doesn't mutate
});

Architecture

┌─────────────────────────────────────────────────────┐
│                      Ewig                           │
├─────────────────────────────────────────────────────┤
│                                                     │
│   ┌─────────────────────────────────────────────┐   │
│   │              Single Atom                    │   │
│   │         (immutable editor_state)            │   │
│   └─────────────────────────────────────────────┘   │
│        │                              │             │
│        ▼                              ▼             │
│   ┌─────────┐                    ┌─────────┐       │
│   │ immer   │   structural       │ lager   │       │
│   │ vectors │   sharing          │ cursors │       │
│   └─────────┘                    └─────────┘       │
│                                                     │
└─────────────────────────────────────────────────────┘

Key Libraries

immer

Persistent immutable data structures for C++:

#include <immer/vector.hpp>

immer::vector<char> buffer = {'h', 'e', 'l', 'l', 'o'};
auto new_buffer = buffer.push_back('!');  // O(log n), shares structure

lager

Unidirectional data-flow architecture:

auto store = lager::make_store<action>(
    model{},
    lager::with_reducer(update),
    lager::with_effect(effect)
);

Relevance to CRDT/Collaborative Editing

Ewig's immutable architecture aligns with CRDT principles:

Integration with crdt-vterm-bridge

The single-atom pattern can be applied to terminal state:

// Terminal state as immutable atom
struct terminal_state {
    immer::flex_vector<line> lines;
    cursor_pos cursor;
    gf3_trit trit;  // GF(3) assignment
};

atom<terminal_state> term_state;

Building

git clone https://github.com/bmorphism/ewig
cd ewig
mkdir build && cd build
cmake .. -DCMAKE_BUILD_TYPE=Release
make
./ewig

Related Skills

• code-refactoring - Immutable refactoring patterns
• bisimulation-game - State equivalence
• gay-mcp - Deterministic UI coloring