LISP

(lĭsp)
n.
A programming language that processes lists. It is widely used in artificial intelligence research.

[lis(t) p(rocessing).]

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For more information on LISP, visit Britannica.com.

(1) (Locator/Identifier Separation Protocol) A proposal from Cisco for reducing the size of the constantly expanding routing tables in the Internet. Working in conjunction with the border gateway protocol (BGP), LISP-identified packets enter the core routers with the destination service provider's IP address, not that of the end user. The provider's edge routers remove the LISP data and deliver the packets to the end users.

(2) (LISt Processing) A high-level programming language used for developing AI applications. Developed in 1960 by John McCarthy, its syntax and structure is very different from traditional programming languages. For example, there is no syntactic difference between data and instructions.

LISP is available in both interpreter and compiler versions and can be modified and expanded by the programmer. Many varieties have been developed, including versions that perform calculations efficiently. The following Common LISP example converts Fahrenheit to Celsius:

   (defun convert ()
     (format t "Enter Fahrenheit ")
     (let ((fahr (read)))
      (format t "Celsius is <126>D"
        (truncate (*(-fahr 32)
            (/ 5 9))))))

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[from ‘LISt Processing language’, but mythically from ‘Lots of Irritating Superfluous Parentheses’] AI's mother tongue, a language based on the ideas of (a) variable-length lists and trees as fundamental data types, and (b) the interpretation of code as data and vice-versa. Invented by John McCarthy at MIT in the late 1950s, it is actually older than any other HLL still in use except FORTRAN. Accordingly, it has undergone considerable adaptive radiation over the years; modern variants are quite different in detail from the original LISP 1.5. The dominant HLL among hackers until the early 1980s, LISP has since shared the throne with C. Its partisans claim it is the only language that is truly beautiful. See languages of choice.

All LISP functions and programs are expressions that return values; this, together with the high memory utilization of LISPs, gave rise to Alan Perlis's famous quip (itself a take on an Oscar Wilde quote) that “LISP programmers know the value of everything and the cost of nothing”.

One significant application for LISP has been as a proof by example that most newer languages, such as COBOL and Ada, are full of unnecessary crocks. When the Right Thing has already been done once, there is no justification for bogosity in newer languages.

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For a list of words related to LISP, see:

• Software, Languages, and Programming - LISP: list processing language; high-level interpretive or compiled language used in artificial intelligence

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