Easy ways to try out and test Lisp syntax?

Question

Clojure has introduced me to the concept of Lisp syntax, and I'm interested, but it's a pain to get the Clojure repl set up and use it on different machines. What other resources are there out there for actually on-the-fly testing and playing with Lisp syntax?

I'm imagining something like a website where you can input rudimentary code, or a browser add-on, or even just a standalone application that steps you through Lisp (something that runs on Linux/Ubuntu).

Haven't been able to find anything like that to start me off in a simple/accessible way.

Answer 1

The SISC Online REPL is exactly what you need. It accepts Scheme syntax, which is a variant of Lisp.

For a standalone app I like PLT Scheme because it seems to work the same on every platform I've tried. I was previously using MIT Scheme on Ubuntu, but decided to switch when I bought a new machine with 64-bit Vista installed.

Answer 2

I've used LispBox in the past. Easy to set up and get going, but I have to admit that Emacs is second nature to me. If you're unfamiliar with that, you may can use another editor, but getting intimate with Emacs will help you live comfortably in Lispville.

Answer 3

I won't edit Lisp code without an editor that does what Emacs will do with the following configuration:

(define-key lisp-mode-shared-map "[" 'insert-parentheses)
(define-key lisp-mode-shared-map "]" 'move-past-close-and-reindent)

The former inserts balanced parentheses. If you give it a numeric prefix argument, it inserts that many nested pairs. By default, it inserts one. If you have a text region marked, it encloses that region in the innermost inserted pair. That means that you'll never open a parenthesis that's not closed.

The latter is harder to explain, as it's used less frequently. It's more of a navigation command than an insertion command. It confirms that you're done editing the current form and moves the cursor up, out, and past it, preparing for the next likely insertion.

With these keys bound, one no longer needs to use the Shift key to access the parentheses. Also, this leaves the parentheses keys bound as normal, for when sexp repair or a literal parenthesis character is required. I stole the bracket keys because they're used so infrequently in Emacs Lisp and Common Lisp. The bracket characters are still accessible with meta key bindings:

(defmacro make-key-inserter (def)
  "Substitute for `self-insert-command'."
  `(lambda (arg)
    (interactive "*P")
    (insert-char ,def (prefix-numeric-value arg))))

(define-key lisp-mode-shared-map "\M-[" (make-key-inserter ?\[))
(define-key lisp-mode-shared-map "\M-]" (make-key-inserter ?\]))

It's not essential to use Emacs, but don't settle for less with another editor that can't at least match this capability. There's also a whole family of commands for navigating and manipulating the sexp tree as a tree. Understanding why that's valuable will require you to fumble around for a while until you stop seeing syntax and start seeing the tree.

Answer 4

At the risk of losing all of my rep points, try newlisp.

Answer 5

Since you're using Ubuntu, I'd just install some of the packages and give them a try.

Common Lisp: apt-get install clisp
Scheme: apt-get install drscheme

These aren't the only packaged implementations, but maybe the easier to get started with. You'll be able to play at a REPL and also run your own scripts through the interpreter.

Answer 6

For learning Lisp the LispWorks personal edition is fine: LispWorks downloads. There are versions for Mac OS X, Windows, Linux and FreeBSD. All have the same user interface capabilities and this includes an editor and listener - plus lots of other tools. On Linux and FreeBSD in currently (LispWorks 5) uses X11/Motif for the GUI - this will change in a future version (LispWorks 6) to GTK. So to run it now under Linux, you need to have the Motif lib installed. Other than that using it is relatively painless. There are some restrictions to it (only 5 hours runtime, then you need to save and restart, ...) and the full version is commercial. But for learning some Lisp basics, it is quite good.

Answer 7

Franz has an online REPL for Allegro Common Lisp.

http://www.franz.com/products/allegrocl/prompt/

Answer 8

BioBike provides a full Common Lisp evaluator through the web (with extras like a knowledge representation system, biocomputing, and an alternative visual langauge as well).

Answer 9

It's not hard to get to a Clojure REPL nowadays.

1. Go to http://build.clojure.org/ and download clojure.jar.
2. Install a JVM.
3. java -jar clojure.jar

This should work on any machine that has a JVM installed.

For more fun, install rlwrap and use rlwrap java -jar clojure.

Answer 10

If you just want to play with LISP, interactively, quickly, GNU Emacs has a LISP interpreter built in, and listening in the *scratch* buffer. Type an S-expression, position immediately after it, and then hit Ctrl-J to evaluate it. Or <ESC>: will put an Eval: prompt in the minibuffer, accept an S-expression, and evaluate it.

You can define functions, using defun, and test things that way. You have access to ALL of the GNU Emacs built-in functions, and anything you have loaded. If you want to keep things around, you can put them in your .emacs file.

Answer 11

codepad.org is a nice simple online way to enter and run code (in many different languages, including Scheme). I use it all the time for testing out snippets of code to use in SO answers.