A Game in F#? Why, yes indeed.

The post says Truffle Wizard was built in F# after the author struggled to reason about state in a Lua-based strategy prototype. F# appealed because it made state transitions easier to follow, reduced boilerplate, and fit a functional style the author found practical for games.

Reading notes

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• Truffle Wizard is a short incremental game written in F#, playable in a browser on desktop or mobile.
• The post is about how the game ended up being written in F# and what it was like to build a game in a functional language.
• The author’s background is mostly in Unity, C#, Objective-C, Flash, ActionScript 3, Lua, and Ruby.
• The motivation came from wanting to reason about state in a systems-heavy strategy game prototype.
• The Lua prototype felt hard to manage because state was hard to track, types needed boilerplate annotations, mutations were easy to introduce, and null checks were common.
• F# for Fun and Profit and railway-oriented programming helped make functional style feel practical and easy to reason about.
• The author wanted immutable-by-default state, rich types, and fewer null checks.
• Unity felt like a poor fit for this approach because it is heavily mutable and object-oriented.
• Raylib felt much better, and the author says F# could drive its loop cleanly.
• Truffle Wizard ultimately used a web stack because its spreadsheet-like UI and scrolling needs fit the web better than Raylib.
• Fable compiles F# to JavaScript, and Feliz provides React support while keeping the code idiomatic in F#.
• The game loop follows an Elmish-style architecture with init, dispatch, update, and render.
• The state is kept in one place, with fields for tick, inventory, unlocks, save log, and view state.
• Saving is simple because the whole state can be serialized and stored in localStorage.
• Messages such as Produce and Tick drive the game, including a timer-based autonomous tick every 250 milliseconds.
• The update function maps messages to state changes in a fairly direct way.
• The render function builds DOM elements with Feliz.
• ChatGPT was used as an F# advisor and helped make the code more concise and idiomatic.
• The author says they did not fully internalize railway-oriented programming, but found F# made prototyping, refactoring, and reasoning about gameplay state much easier.
• The author expects future side projects to use F# again, probably with Raylib, and wonders about a future Fable target for Lua.