Dotenv Config

Read a project-local .env file with File::Read, decode scalar values at the boundary with Decode<T>, and reshape the result into a typed runtime config.

Source

examples/dotenv-config/.env

APP_ENV=prod
PORT=9000
DEBUG=true
APP_NAME="Rank Docs"

examples/dotenv-config/main.rank

/// Reads a project-local dotenv file through File::Read with Decode<T>
/// at the flat text boundary and reshapes it into a typed runtime config.

use std::Decode
use std::File
use std::Path

AppEnv = `dev` | `prod`
Port = 8080 | 9000

DotenvConfig = Object {
  APP_ENV: AppEnv,
  PORT?: Decode<Port>,
  DEBUG?: Decode<bool>,
  APP_NAME: string,
  ...: string,
}

AppConfig = Object {
  name: string,
  env: AppEnv,
  port: number,
  debug: bool,
  source: Object {
    path: string,
    format: `dotenv`,
  },
}

response = File::Read<DotenvConfig> {
  path: Path::join([`.env`]),
  format: `dotenv`,
}

raw = response.body

config: AppConfig = {
  name: raw.APP_NAME,
  env: raw.APP_ENV,
  port: raw.PORT ?? 8080,
  debug: raw.DEBUG ?? false,
  source: {
    path: response.ctx.path,
    format: `dotenv`,
  },
}

pub main = || config

Output

{
  "name": "Rank Docs",
  "env": "prod",
  "port": 9000,
  "debug": true,
  "source": {
    "path": ".env",
    "format": "dotenv"
  }
}

Key concepts

• format: dotenv — File::Read can decode .env-style flat text files as an explicit file dependency rather than ambient host environment.
• Boundary decoding with Decode<T> — PORT?: Decode<Port> and DEBUG?: Decode<bool> turn dotenv text into typed scalar values as the file is read.
• Flat text model — each dotenv entry stays one key/value text boundary; nested objects and lists are not decoded from a single entry.
• response.ctx — file provenance stays explicit, so the resulting config can still carry the source path and format.
• Defaults after decode — optional decoded fields combine cleanly with ?? once the boundary parsing has succeeded.

Run it

rank examples/dotenv-config