Lisp, short for "LISt Processing," is a family of programming languages that share a distinctive parenthesis-based syntax primarily centered around the manipulation of symbols and lists. It is one of the oldest high-level programming languages, originally invented in the late 1950s, and it has evolved significantly over the decades. Lisp is particularly known for its powerful features such as dynamic typing, garbage collection, and first-class functions, making it suitable for AI research, symbolic computation, and rapid prototyping.
Lisp was created by John McCarthy in 1958 as a mathematical notation for computer programs and as a practical means of implementing AI. The language was derived from the lambda calculus, a formal system in mathematical logic and computer science. The first implementation was conducted on the IBM 704, and soon after, numerous dialects emerged, each adding its own features and complexities.
Several notable dialects of Lisp have emerged over time, including Common Lisp and Scheme. Common Lisp was standardized in the 1980s to unify various dialects, while Scheme, which emphasizes functional programming and minimalism, gained popularity in academia. Lisp influences can be seen in many modern programming languages, especially those that support functional programming paradigms, such as Clojure, Racket, and even languages like Python and Ruby.
Today, Lisp is not among the most popular programming languages but remains influential, particularly in research, AI, and education. The community actively develops newer dialects like Clojure, which runs on the Java Virtual Machine (JVM) and focuses on concurrent programming.
Lisp employs a unique syntax using parentheses to denote expressions, with code represented in symbolic expressions (S-expressions). For example:
(+ 1 2)
This expression represents the addition of 1 and 2.
Functions in Lisp can be passed as arguments, returned from other functions, and assigned to variables:
(defun square (x) (* x x))
(mapcar #'square '(1 2 3 4)) ; returns (1 4 9 16)
Lisp is dynamically typed, allowing variables to hold values of any data type without prior declaration:
(setq x 10) ; x is now a number
(setq x "hello") ; x is now a string
Lisp features powerful macro systems that allow developers to create custom syntactic constructs:
(defmacro when (condition &body body)
`(if ,condition
(progn ,@body))
)
The if and cond forms facilitate control flow in Lisp:
(if (> x 0)
(print "Positive")
(print "Non-positive"))
Lisp treats lists as fundamental data structures:
(setq my-list '(1 2 3 4))
(car my-list) ; returns 1
(cdr my-list) ; returns (2 3 4)
Functions are defined using the defun construct:
(defun factorial (n)
(if (= n 0)
1
(* n (factorial (- n 1)))))
Common Lisp includes an object-oriented system known as the Common Lisp Object System (CLOS):
(defclass person ()
((name :initarg :name :accessor person-name)
(age :initarg :age :accessor person-age)))
(defmethod say-hello ((p person))
(format t "Hello, my name is ~A and I'm ~A years old."
(person-name p) (person-age p)))
Lisp provides a sophisticated error handling mechanism using handler-case:
(handler-case
(/ 1 0)
(division-by-zero () (print "Caught division by zero!")))
Continuations are supported in some dialects, allowing the program to save and restore execution states:
(call-with-current-continuation
(lambda (k)
(k 10)))
Several Integrated Development Environments (IDEs) and compilers cater to Lisp programming. Popular choices include:
To build a Lisp project, you usually create a file with a ".lisp" or ".lsp" extension. Using SBCL, a typical workflow may involve loading your project from the REPL:
(load "my-project.lisp")
For projects using Quicklisp, a library manager, dependencies can be easily managed and loaded.
Lisp is particularly known for its applications in artificial intelligence, symbolic computation, and academia, but it also finds uses in:
Lisp is often compared to:
Translating from Lisp to other languages is often done using source-to-source translation tools. For example, the following tools exist:
Each of these tools provides specific mappings ensuring that the core functionalities of Lisp can be effectively represented in the target languages. For more complex translations, manual refactoring may be required, especially for heavily macro-optimized code.