For those who like to write Scheme without leaving Emacs, Geiser is probably the way to go.

The Racket guide for Emacs also recommends to install Quack, which I happened to try long ago for an introductory course in programming for Bioinformatics where we were using Scheme (I was using Chicken Scheme at that time).

I believe DrRacket (formerly PLT Scheme) is really a great software to learn Scheme and do serious stuff with it, including computational science. I know people would not necessarily consider Racket as a pure Scheme language. By the way, here are some of the most upvoted questions on Stack Overflow:

Beside Doug Williams science collection, Racket now includes scientific packages like plot and math/statistics.

For example, using a toy demo from Racket website, here is how it looks under the native Mac app:

And here is the same script processed through Emacs Geiser:

With Emacs, you just have to M-x run-geiser to start the REPL (it is pretty fast to come up, unlike Clojure REPL). However, since Geiser targets both Racket and Guile, I decided to compile Guile. I tried to install Guile some time ago, following a suggestion on Cross Validated where I provided a brief illustration with Scheme. But it soon reached to the point where I had too much dependencies to manage and I finally gave up. This time, it works perfectly well, and I suspect that this is because I added all those dependencies in the mean time (in particular, to install mu).

Finally, I recently learned about Pyret (and, as a side-effect, of Frog):

Pyret is a programming language designed to serve as an outstanding choice for programming education while exploring the confluence of scripting and functional programming.

### Sidenote

Emacs 24.4 is available for OS X on http://emacsformacosx.com/ (check the Nightlies builds), and it comes with pretiffy1, see also What’s new in Emacs 24.4.

By the way, I learned that Emacs 24.3 suffers from a problem when rendering sRGB color, which explains why I got some strange problems with powerline.2

1. I use pretty-lambdada.el at the moment. [return]
2. Other issues came around when I used the solarized theme. Now, I switched to gruber-darker theme, so it doesn’t bother me anymore. [return]