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