Effect Bot

A Discord bot built with Effect and discord.js, running on Bun. A learning project for exploring Effect's approach to dependency injection, layered architecture, and typed error handling.

Prerequisites

• Bun (latest)
• A Discord application with a bot token

Setup

1. Install dependencies:

   bun install

2. Copy the example env file and fill in your values:

   cp .env.example .env.local

   Variable	Description
   NODE_ENV	development or production
   BOT_TOKEN	Your Discord bot token
   CLIENT_ID	Your Discord application's client ID
   GUILD_ID	The server to register commands in

3. Deploy slash commands to your guild:

   bun run deploy:dev

4. Start the bot:

   bun run dev

Project Structure

src/
├── index.ts              # Entry point — creates the client and wires up layers
├── config/
│   ├── index.ts          # Exports AppConfig (dev/prod) and Config namespace
│   └── bot.ts            # Bot service tag + config layers (token, clientId, guildId)
├── structures/
│   ├── command.ts        # Command interface and factory
│   └── event.ts          # Event interface and factory
├── layers/
│   ├── index.ts          # Merges AppConfig + registries into AppLayer
│   ├── command-registry.ts  # Auto-discovers commands from src/commands/
│   └── event-registry.ts    # Auto-discovers events from src/events/
├── commands/
│   └── ping.ts           # Example slash command
├── events/
│   ├── ready.ts          # Logs when the bot connects
│   └── interactionCreate.ts  # Routes interactions to commands
scripts/
└── deploy-commands.ts    # Registers slash commands with the Discord API

Adding a Command

Create a new file in src/commands/ — it will be auto-discovered at startup.

// src/commands/hello.ts
import { MessageFlags } from "discord.js";
import { Effect } from "effect";
import { Command } from "@/structures/command";

export const hello = Command.make({
  name: "hello",
  description: "Say hello",
  execute: (interaction) =>
    Effect.promise(() =>
      interaction.reply({ content: "Hello!", flags: MessageFlags.Ephemeral })
    ),
});

Then redeploy commands so Discord knows about it:

bun run deploy:dev

Adding an Event

Create a new file in src/events/ — also auto-discovered.

// src/events/messageCreate.ts
import { Effect } from "effect";
import { Event } from "@/structures/event";

export const messageCreate = Event.make({
  name: "messageCreate",
  handle: (message) => Effect.log(`Message from ${message.author.username}`),
});

Scripts

Script	Description
bun run dev	Start the bot
bun run deploy:dev	Deploy slash commands (guild, development)
bun run deploy:prod	Deploy slash commands (guild, production)
bun run check	Lint/format check via ultracite
bun run fix	Auto-fix lint/format issues

How It Works

The bot uses Effect's Layer system for dependency injection:

• Config.Bot — provides bot credentials from environment variables
• CommandRegistry — scans src/commands/ and builds a Map<string, Command>
• EventRegistry — scans src/events/ and builds a Map<string, Event>
• AppLayer — merges all the above into a single layer provided to the main program

At startup, the bot iterates over registered events and binds them to the Discord client. Commands are resolved from the registry when an interactionCreate event fires.