drift

Drift is a Gleam library for creating asynchronous pure functional cores, which can be wrapped with different I/O and timer implementations. These cores can be used on both the Erlang and JavaScript targets. Side effects are tracked by producing outputs on every step, and executing the side effects is left to be done by a wrapping runtime.

When to use drift?

You might want to use drift if:

• You have logic written in Gleam you want to run on both Erlang and JS, or in environments with very different I/O in some other way.
• Your logic has a lot of I/O or timers interleaved with other logic.
• You want to run deterministic (snapshot) tests on your logic.

You might want to avoid drift if:

• Your I/O and timer logic is simple, with little interleaving. In this case, you can probably easily separate the pure parts without using drift, making the implementation simpler.
• You care a lot about performance. Given how drift is built, it will always have some performance overhead.

Packages

This repository contains the following packages:

• drift contains the core utilities for writing pure functional logic.
• drift_actor wraps a core written with drift in an OTP actor.
• drift_js wraps a core written with drift in an event loop on the JS target.
• drift_record contains utilities to record the inputs and outputs of a drift core in a snapshot-testing friendly manner.

The examples directory contains a simple drift core that can fetch cat facts, and wrappers for both the Erlang and JavaScript targets.