About Wren

Wren is a small, fast, class-based concurrent scripting language. Think Smalltalk in a Lua-sized package with a dash of Erlang and wrapped up in a familiar, modern syntax.

• Small. The VM is under 4,000 semicolons of readable and lovingly-commented C.

• Fast. A smart, single-pass compiler produces tight, efficient bytecode.

• Class-based. Classes and objects are front and center.

• Concurrent. Lightweight fibers are built into the language.

• Scripting. Embeddable, no dependencies, a small standard library, and an easy-to-use C API.

The VM

The heart of Wren is the VM. The Wren Virtual Machine is the core of the language and executes all Wren source code. It is just a library, not a standalone application. It’s designed to be embedded in a larger host application.

You can find Wren embedded in such projects as:

• TIC-80 - a fantasy computer for making, playing and sharing tiny games (similar to PICO8).
• DOME - a cross-platform framework for making games.
• luxe - a cross-platform, rapid development game engine for making games.
• Wren Console - a Wren REPL and CLI written largely in Wren itself.

You can even embed Wren inside your own projects. For Exercism purposes the host application we'll be using is Wren Console - allowing us to run and test our Wren scripts from the terminal.

Why Wren?

Wren was originally created by Bob Nystrom of Crafting Interpreters fame. He has more than a few languages under his belt, but he explains specifically what led to the creation of Wren:

There are a few scripting languages used for embedding in applications. Lua is the main one. TCL used to be. There’s also Guile, increasingly JavaScript, and some applications embed Python. I’m an ex-game developer, so when I think “scripting”, I tend to think “game scripting”.

Lua is nice: it’s small, simple, and fast. But—and I don’t mean this as a criticism—it’s also weird if you’re used to languages like C++ and Java. The syntax is different. The semantics, especially the object model are unusual. Anyone can get used to 1-based indexing, but things like metatables really show that objects were bolted onto Lua after the fact.

I think there’s room for a language as simple as Lua, but that feels natural to someone with an OOP background. Wren is my attempt at that.

Trying it

You can give it a quick try inside your web browser (without installing a thing). If you want to experiment with Wren wrapped up in a slick UI you might take a look at Wren Playground.