What are the differences between Clojure, Scheme/Racket and Common Lisp?

Question

I know they are dialects of the same family of language called lisp, but what exactly are the differences? Could you give an overview, if possible, covering topics such as syntax, characteristics, features and resources.

Answer 1

Don't forget about Lisp-1 and Lisp-2 differences.

Scheme and Clojure are Lisp-1:
That means both variables and functions names resides in same namespace.

Common Lisp is Lisp-2:
Function and variables has different namespaces (in fact, CL has many namespaces).

Answer 2

Gimp is written in Scheme :)

In fact allot of software some folks think might be written in C++ was probably done under the Lisp umbrella, its hard to pick out the golden apples out of the bunch. The fact is C++ was not always popular, it only seems to be popular today because of a history of updates. For the lesser half of the century C++ didn't even utilize multithreading, it was where Python is today a cesspool of useless untested buggy glue code. Fasterforward a little and now we are seeing a rise in functional programming, its more like adapt or die. I think Java has it right as far as the adapt part is concerned.

Scheme was designed to simplify the Lisp language, that was its only intent except it never really caught on. I think Clojure does something similar its meant to simplify Scheme for the JVM nothing more. Its just like every other JVM language just there to inflate the user experience, only to simplify writting boilerplate in Java land.

Answer 3

They all have a lot in common:

• Dynamic languages
• Strongly typed
• Compiled
• Lisp-style syntax, i.e. code is written as a Lisp data structures (forms) with the most common pattern being function calls like: (function-name arg1 arg2)
• Powerful macro systems that allow you to treat code as data and generate arbitrary code at runtime (often used to either "extend the language" with new syntax or create DSLs)
• Often used in functional programming style, although have the ability to accommodate other paradigms
• Emphasis in interactive development with a REPL (i.e. you interactively develop in a running instance of the code)

Common Lisp distinctive features:

• A powerful OOP subsystem (Common Lisp Object System)
• Probably the best compiler (Common Lisp is the fastest Lisp according to http://benchmarksgame.alioth.debian.org/u64q/which-programs-are-fastest.html although there isn't much in it.....)

Clojure distinctive features:

• Largest library ecosystem, since you can directly use any Java libraries
• Vectors [] and maps {} used as standard in addition to the standard lists () - in addition to the general usefullness of vectors and maps some believe this is a innovation which makes generally more readable
• Greater emphasis on immutability and lazy functional programming, somewhat inspired by Haskell
• Strong concurrency capabilities supported by software transactional memory at the language level (worth watching: http://www.infoq.com/presentations/Value-Identity-State-Rich-Hickey)

Scheme distinctive features:

• Arguably the simplest and easiest to learn Lisp
• Hygienic macros (see http://en.wikipedia.org/wiki/Hygienic_macro) - elegantly avoids the problems with accidental symbol capture in macro expansions

Answer 4

The people above missed a few things

1. Common Lisp has vectors and hash tables as well. The difference is that Common Lisp uses #() for vectors and no syntax for hash tables. Scheme has vectors, I believe

2. Common Lisp has reader macros, which allow you to use new brackets (as does Racket, a descendant of Scheme).

3. Scheme and Clojure have hygienic macros, as opposed to Common Lisp's unhygienic ones

4. All of the languages are either modern or have extensive renovation projects. Common Lisp has gotten extensive libraries in the past five years (thanks mostly to Quicklisp), Scheme has some modern implementations (Racket, Chicken, Chez Scheme, etc.), and Clojure was created relatively recently

5. Common Lisp has a built-in OO system, though it's quite different from other OO systems you might have used. Notably, it is not enforced--you don't have to write OO code.

6. The languages have somewhat different design philosophies. Scheme was designed as a minimal dialect for understanding the Actor Model; it later became used for pedagogy. Common Lisp was designed to unify the myriad Lisp dialects that had sprung up. Clojure was designed for concurrency. As a result, Scheme has a reputation of being minimal and elegant, Common Lisp of being powerful and paradigm-agnostic (functional, OO, whatever), and Clojure of favoring functional programming.