Question

I’ve played around with a few functional programming languages and really enjoy the s-expr syntax used by Lisps (Scheme in particular).

I also see the advantages of working in a purely functional language. Therefore:

Are there any purely functional Schemes (or Lisps in general)?

Answer 1

Probably not, at least not as anything other than toys/proofs of concept. Note that even Haskell isn’t 100% purely functional–it has secret escape hatches, and anything in IO is only “pure” in some torturous, hand-waving sense of the word.

So, that said, do you really need a purely functional language? You can write purely functional code in almost any language, with varying degrees of inconvenience and inefficiency.

Of course, languages that assume universal state-modification make it painful to keep things pure, so perhaps what you really want is a language that encourages immutability? In that case, you might find it worthwhile to take a look at Clojure‘s philosophy. And it’s a Lisp, to boot!

As a final note, do realize that most of Haskell’s “syntax” is thick layers of sugar. The underlying language is not much more than a typed lambda calculus, and nothing stops you from writing all your code that way. You may get funny looks from other Haskell programmers, though. There’s also Liskell but I’m not sure what state it’s in these days.

On a final, practical note: If you want to actually write code you intend to use, not just tinker with stuff for fun, you’ll really want a clever compiler that knows how to work with pure code/immutable data structures.