Scheme in JavaScript

A while back, I wrote a little Scheme interpreter in JavaScript. It only supports very basic Scheme constructs like lambdas and numbers. I did not add macros or continuations. This also means some features you’d normally expect, like let, are missing because I was planning to implement let as a macro but never finished the macro system!

I also wrote a very basic REPL for it. You can play around a bit.

Try something basic like

(define (fib n)
  (if (or (= n 0) (= n 1))
    n
    (+ (fib (- n 1)) (fib (- n 2)))))

Try It!

Here is a simple JavaScript REPL for my Scheme interpreter. Type in the very top row. Try something simple like (+ 1 2).

Embedding

I also added some cute JavaScript-specific features into the language. You can embed JavaScript code inside your Scheme code using backticks:

(cons `function () { return 10 }` 11)

You can also embed Scheme code directly into your page using <script> tags:

<script language="scheme">
  (define (avg ls)
    (/ (accumulate + 0 ls) (length ls)))
</script>

Now the avg function is available to other Scheme code you have on your page. Unfortunately, this does not work with scripts from a different file. So <script language="scheme" src="foo.scm"> won’t work.