Orb: Write WebAssembly with Elixir

Docs | Examples

Write WebAssembly with the power of Elixir as your compiler:

• Use Elixir’s module system to break problems down and then compose them together.
• Chain function calls together with the pipe |> operator.
• Publish reusable code with the Hex package manager.
• Write unit tests using Elixir’s built-in ExUnit.
• Reduce boilerplate with Elixir’s powerful macro system.
• Run dynamic Elixir code at compile time e.g. talk to the rest of your Elixir application, call out to an Elixir library, or make network requests.
• Compile modules on-the-fly e.g. use feature flags to conditionally compile code paths or enable particular WebAssembly instructions, creating a custom “tree shaken” WebAssembly module per user.

Status

Orb is alpha in active development. My aim is to refine the current feature set and complete a .wasm compiler (current it compiles to WebAssembly’s .wat text format) in order to get to beta.

Libraries

• Orb (alpha): Write WebAssembly 1.0 in Elixir.
• SilverOrb (work-in-progress): Batteries-included standard library for Orb.
• OrbExtismPDK (coming later): Write Extism plugins in Elixir with Orb.

Installation

Add orb to your list of dependencies in mix.exs:

def deps do
  [
    {:orb, "~> 0.1.0"}
  ]
end

Example

defmodule CalculateMean do
  use Orb

  global do
    @tally 0
    @count 0
  end

  defw insert(n: I32) do
    @tally = @tally + n
    @count = @count + 1
  end

  defw calculate_mean(), I32 do
    @tally / @count
  end
end

This can be converted to WebAssembly text format (wat):

wat = Orb.to_wat(CalculateMean)
# """
# (module $CalculateMean
#   (global $count (mut i32) (i32.const 0))
#   (global $tally (mut i32) (i32.const 0))
#   (func $insert (export "insert") (param $element i32)
#     (i32.add (global.get $count) (i32.const 1))
#     (global.set $count)
#     (i32.add (global.get $tally) (local.get $element))
#     (global.set $tally)
#   )
#   (func $calculate_mean (export "calculate_mean") (result i32)
#     (i32.div_s (global.get $tally) (global.get $count))
#   )
# )
# """

Write this out as a .wat WebAssembly text file:

File.write!("example.wat", wat)

You can then compile this to a .wasm WebAssembly file using wat2wasm from the WebAssembly Binary Toolkit:

wat2wasm example.wat

Or you can execute it directly in Elixir with OrbWasmtime:

alias OrbWasmtime.Instance

# Run above example
inst = Instance.run(CalculateMean)
Instance.call(inst, :insert, 4)
Instance.call(inst, :insert, 5)
Instance.call(inst, :insert, 6)
assert Instance.call(inst, :calculate_mean) == 5

Note there is another excellent Elixir Wasmtime wrapper out there called Wasmex, you may want to check that out too.

Composing modules

You can compose modules together using Orb.include/1:

defmodule Math do
  use Orb

  defw square(n: I32), I32 do
    n * n
  end
end

defmodule SomeOtherModule do
  use Orb

  Orb.include(Math)

  defw magic(), I32 do
    Math.square(3)
  end
end

Use cases

• Parsers
• State machines
• Formatters & string builders
• HTTP endpoint that can be deployed agnostically to the server or edge.
• Interactive UI controls
• Write a HTML component and run it in:
  • Phoenix LiveView & dead views
  • In the browser using <wasm-html> custom element
• LiveView and its server rendering is a fantastic default, but the latency can be noticeable for certain UI interactions. With Orb you could use Elixir to write a WebAssembly module that then runs in the user’s browser.
• Animation that runs fast in the browser and also works on the server
• Code generators

Why WebAssembly?

• It runs on all of today’s major platforms: browser, server, edge, mobile, laptop, tablet, desktop.
• Universal/isomorphic components (ones that run on the server and browser) are possible in React and Next.js, but they have many different flavours and can get pretty complex for a system that was meant to be declarative.
• Like HTML and CSS it’s backwards compatible, which means WebAssembly you author today will be guaranteed to still work in a decade or longer.
• It’s memory-safe and sandboxed. It can’t read memory outside of itself, only what has been explicitly passed into it. It can even be timeboxed to run for a maximum duration.
• It’s fast.

Why develop Orb in Elixir?

Here are the reasons I chose to write Orb in Elixir.

• Established language:
  • Has package manager.
  • Has composable modules with alias & use.
  • Has syntax highlighting in IDEs, GitHub, and in highlighting libraries.
  • Has language server with autocomplete.
  • Has documentation system.
  • Has unit test library.
  • Has CI integration.
  • Has linting.
  • Integrates with native libraries in Rust and Zig.
  • Has upcoming type system.
• Established frameworks:
  • Can integrate with Phoenix LiveView.
  • Can connect to cloud, databases.
  • Can integrate with Rust.
• Community that is friendly and collaborative.
• Can be extended with additional functions and macros:
  • Unlike say C’s basic string-inserting preprocessor, Elixir is a full programming language without constraints.
  • We can read files or the network and then generate code.
  • You can create your own DSL. Want to enforce immutable-style programming? Want to add pattern matching? Design your own DSL on top of Orb for it.