♞ chess

Chess against a built-in engine — four strengths, every rule of the game, and a board that glides — built with miso and compiled to WebAssembly.

Play it live: https://chess.haskell-miso.org

• ♟ The whole game: castling both ways, en passant, promotion to any piece, check and checkmate, and every draw — stalemate, threefold repetition, the fifty-move rule, insufficient material
• 🧠 A real engine: negamax alpha-beta with a capture-only quiescence search, MVV-LVA move ordering, and a material + piece-square evaluation with an endgame king table. Four strengths from one ply to four; the casual level picks among its near-best moves so it stays beatable
• 📊 An evaluation bar beside the board, a hint that marks the move the engine would play for you, and undo that takes back a full move — even after the game ends, so you can replay the ending
• 📜 The game record in standard algebraic notation with proper disambiguation (Nbd2, R1a3, Qa1b2), check and mate suffixes, and a Copy PGN button at the end
• 🖐 Tap or drag to move: legal targets are shown as dots and capture rings, the last move stays lit, a pinned piece tells you it can't move, and pawns get a promotion tray
• 🔄 Play either colour (or let the engine choose); flipping the board spins it in place while the pieces stay upright
• ⌨️ Keys: U undo, F flip, H help, M sound, N title, esc cancel
• 📱 Mobile-first: the board fills the phone, the ledger tucks beneath it, and the eval bar turns horizontal
• 🔊 Sound synthesized live with the Web Audio API — wooden knocks for moves, a heavier one for captures, a small bell for check (zero audio assets)
• 🌙 A chess study at night: one pool of light, a board of bone and slate stone on a dark plinth, Cormorant Garamond and Manrope, and only two accents — mint for what you can do, amber for what just happened — built on Miso.Lens, Miso.CSS, and Miso.CSS.Color

The engine

The rules and the search are pure modules that know nothing about the DOM:

• Chess is the rulebook: move generation, legality with a pin-aware fast path, applyMove, status with every draw rule, FEN in both directions, SAN, and perft
• Engine is the search: negamax alpha-beta, quiescence, move ordering, evaluation, and the four levels. Randomness comes in as a supply of uniform doubles so every decision is reproducible
• Every piece carries a stable id, which is what lets the view animate a piece sliding from square to square

Build (WASM)

nix develop .#wasm --command bash -C 'make && make serve'

Tests

The rules and the engine are tested natively:

cabal test

Checks include: perft node counts on the standard positions (the start position to depth 4, Kiwipete, and the pin/en-passant/promotion positions), castling and pin legality, every draw rule, SAN disambiguation and suffixes, FEN round trips, and engine sanity — it finds mates in one, takes free material, avoids a back-rank mate, and moves within a time budget.

CI builds with nix and deploys public/ to GitHub Pages on pushes to master.