mbuhot

The Ultimate Guide to Gleam's Typed Actors

How Gleam builds type-safe concurrent programming on the BEAM

The BEAM virtual machine (which runs Erlang, Elixir, and now Gleam) is renowned for its actor model concurrency. But traditionally, message passing has been untyped - any process can send any message to any other process, leading to runtime crashes when unexpected messages arrive.

Gleam changes this game entirely by building a sophisticated type-safe layer on top of BEAM's primitives. In this deep dive, we'll explore exactly how Gleam achieves compile-time type safety for concurrent programming, revealing the elegant implementation strategies that make it all work.

The Foundation: BEAM Processes and Raw Message Passing

mbuhot

defmodule Opaque.User do
  @moduledoc """
  Demonstrates a ridiculous method for enforcing that a type remains in a valid state using a closure and internal secret
  """
  
  alias __MODULE__

  # Ensure that the internal closure can only be called from within this module
  @update_key :crypto.strong_rand_bytes(8)

mbuhot

namespace System.Text.Json

open System
open System.Collections.Generic
open System.Text.Json.Serialization

// Converts Option<T> to/from JSON by projecting to null or T
type OptionValueConverter<'T>() =
    inherit JsonConverter<'T option>()

mbuhot

defmodule TextProcess do
  def generate_files(num_files, lines_per_file) do
    Enum.each(1..num_files, fn i ->
      filename = "data/test_#{i |> Integer.to_string() |> String.pad_leading(3, "0")}.csv"

      File.open!(filename, [:write], fn file ->
        Enum.each(1..lines_per_file, fn _ ->
          IO.puts(file, line())
        end)
      end)

mbuhot

defmodule ExqStatsD do
  @behaviour Exq.Middleware.Behaviour

  alias Exq.Middleware.Pipeline

  @moduledoc """
  This behavior will send stats to statsd endpoint for monitoring.
  """

  require Logger

mbuhot

defmodule NumberToWord do
  @spec say(integer) :: String.t
  def say(n), do: n |> say_io() |> IO.iodata_to_binary()

  @spec say_io(integer) :: iodata
  def say_io(1), do: "one"
  def say_io(2), do: "two"
  def say_io(3), do: "three"
  def say_io(4), do: "four"
  def say_io(5), do: "five"

mbuhot

defmodule Scrabble do
  def score("", n), do: n
  def score("A" <> rest, n), do: score(rest, n + 1)
  def score("B" <> rest, n), do: score(rest, n + 3)
  def score("C" <> rest, n), do: score(rest, n + 3)
  def score("D" <> rest, n), do: score(rest, n + 2)
  def score("E" <> rest, n), do: score(rest, n + 1)
  def score("F" <> rest, n), do: score(rest, n + 4)
  def score("G" <> rest, n), do: score(rest, n + 2)
  def score("H" <> rest, n), do: score(rest, n + 4)

mbuhot

defmodule MyService do
  def foo() do
    GenServer.call(:my_service, :foo)
  end
end

defmodule MyServiceFake do
  use GenServer
  def handle_call(:foo, _from, state) do
    {:reply, :fake, state}

mbuhot

title	search
Simple API	true

Simple API

A Simple API.

mbuhot

{
  "swagger": "2.0",
  "info": {
    "version": "1.0.0",
    "title": "Simple API",
    "description": "A Simple API.",
    "termsOfService": "Use at your own risk!",
    "contact": {
      "name": "Joe P. Coder"
    },