Effect CommunityEC
Effect Community•6mo ago
Al @ Module

Understanding `Layer.launch` and its behavior can be a bit tricky, especially if you're new to th...

I'm trying to understand how Layer.launch works and what "keeps it alive until interrupted" from the docs means. I've tried searching the docs, reading through the HTTP Server code and searching Discord but I can't quite find a clear understanding. I suspect I'm missing a deeper understanding of the relevant building blocks and so I would be happy to be pointed to docs to learn about those too.

I know this code probably doesn't make sense but could someone explain what's going on here under the hood, what it means for the Example layer to be being kept alive and why the last console log isn't reached? Thank you!

import { Console, Context, Effect, Layer } from "effect";
import { NodeRuntime } from "@effect/platform-node";

class Example extends Context.Tag("Example")<
  Example,
  { readonly data: string }
>() {}

const ExampleLive = Layer.succeed(Example, { data: "Example" });

const program = Effect.gen(function* () {
  yield* Console.log("Starting...");
  yield* Layer.launch(ExampleLive);
  yield* Console.log("Not reached");
});

NodeRuntime.runMain(program);
Effect Documentation
Managing Layers
Learn how to use layers in Effect to manage service dependencies and build efficient, clean dependency graphs for your applications.
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