Why Functional JavaScript?

I’m teaching myself functional programming (FP). I first noticed it in Ruby, even though it’s been in JavaScript all along. I’m working my way through Structure and Interpretation of Computer Programs (SICP), and The Little Schemer books, so I’m learning Scheme and Lisp too.

When studying FP, I generally use JavaScript and Scheme. My FP examples here are usually in JavaScript:

  • It’s available everywhere, and most programmers are comfortable reading it.
  • It’s closer to Scheme than Ruby is, so the examples translate better. In fact, Douglas Crockford notes: “JavaScript has much in common with Scheme. It is a dynamic language. It has a flexible datatype (arrays) that can easily simulate s-expressions. And most importantly, functions are lambdas. Because of this deep similarity, all of the functions in The Little Schemer can be written in JavaScript.”

I include Ruby or Scheme, though, if it seems appropriate.

I often use the JavaScript Shell, or its big brother, the JavaScript Development environment, because I haven’t found or built a JavaScript REPL as nice as Dr. Scheme.


Most current JavaScript implementations are slow with recursion and closures…two cornerstones of functional programming.

I don’t worry about this, because my examples are not meant to be dropped into production systems without thought and testing. I write production-ready code at work; here, I play and explore. We do use some functional JavaScript where I work, but it’s where the performance is acceptable, and the imperative alternative would be too unwieldly.

History seems to show that performance is a short-term concern, and better programming techniques are a long-term concern. It also seems that there are no inherent reasons JavaScript is slow; more performant implementations may be in our future.

Why not Haskell or Erlang?

…or OCaml, Scala, F#, Clojure? I’m getting there. SICP and The Little Schemer books are more than enough for me right now.


7 thoughts on “Why Functional JavaScript?

  1. I’ve seen it, but haven’t had the chance to dive in yet. Just from the front page, it looks like it could serve as a syllabus for further exploration into functional programming…thanks for passing it on!

  2. Daniel, great post. I have gone from loathing Javascript to really enjoying using it, in large part because I have discovered its functional programming potential. Getting to know the proptotype.js code helped me explore that. Doing a lot of Ajax and event handling coding made me familiar with first-class procedures.

    I too am working through SICP, through the MIT OpenCourseWare course of the same name, with a few other brave souls. I read the Little Schemer last year, and it really helped prepare me for a lot of the concepts in SICP.

    Good luck with functional Javascript. I’ll keep an eye on your feed, and I look forward to reading more about your explorations.

  3. If you are going to do any of the examples in SICP book, I would be curious how you will do a metacircular evaluator (chapter 4, I believe). I guess that will not be necessary if you are strictly doing functional programming in Javascript, but I would be interested in seeing what you come up with. :-)

  4. @goodmike, I’ve been using the SICP 1981 lectures, but I might check out the MIT stuff…that’s a great idea, I can’t believe it didn’t occur to me.

    @Ralph, when I get that far, I’ll certainly do the metacircular evaluator in Scheme. Maybe I’ll give it a go in JavaScript too, though, and see how far I get. My point in this post was really to say “when I _blog_ about FP, the examples are in JavaScript, because…” I’ve come to enjoy Scheme, and I’ll keep my eye open for ways to use it on-the-job, but JavaScript is generally an easier sell.

    @Mark, I’ve never heard of MozRepl, I’ll check it out. There’s probably an emacs hacker inside me, waiting to come out; MozRepl is one more reason for me to seriously sit down with it. I expect it’ll pay off, but it’s always a question of how to use my scarce time: FP? blogging? linux? emacs? The autodidact’s curse is that you never really graduate.

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