The Grove II is a complete, self-contained development environment for imperative and Faux-O programming in JavaScript. You can use it here: https://druidic.github.io/grove-ii/.

In plain English: you can write and run code in the browser, and it's more or less like programming on a state-of-the-art computer from 1986 or so. Except it's better, because you get to write JavaScript instead of BASIC or C or FORTRAN.

It currently supports:

• A simple, user-friendly command line interface with some novel creature comforts.
• Efficient, native emulation of synchronous operations, like sleep() and blocking I/O.
• Persistence of both code and program state in localStorage.
• Exporting code and data to files so programs can be shared or moved between browsers.

Planned features:

• A graphical mode using HTML5 Canvas.

Perhaps the most surprising thing about programming on the Grove II is the synchronous, imperative idioms it supports. In the past, these idioms were alien to JavaScript programming, but with ES6, they have become technically feasible.

Here's an example of a Grove II program. And yes, it does what you'd expect.

function* Main() {
  while (true) {
    log('HELLO, WORLD')
    yield sleep(1)
  }
}

Not only does the sleep() call actually cause a delay in the execution of the loop, the user can break out of the loop during the program's execution by pressing the escape key.

The initial version of the Grove had a strictly functional API. Why does the Grove II favor imperative programming?

Perhaps the most compelling reason is that it's easy to write functional programs in an imperative environment, but difficult to write imperative programs in a functional environment. If you really like functional programming and want nothing to do with this imperative nonsense, you're free to write programs on the Grove II in a functional style.

The second reason is that imperative programs are far easier to construct for simple tasks. For applications as diverse as text adventures, financial calculators, and wizard name generators, imperative programming (perhaps with a functional core) is the most obvious solution.

The idea that functional programs would be easier to test didn't really pan out. The easiest way to test simple Grove programs was still through the UI, and at that boundary it doesn't matter for testing purposes whether the program is written in a functional or imperative style.

One of my design goals for the original Grove was to reduce the barrier to starting a new project, but many aspects of the Grove's design, including the forced functional paradigm, got in the way of that goal. I've since realized that the functional-only approach was the wrong design decision.