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104-635: Common Lisp ( CL ) is a dialect of the Lisp programming language , published in American National Standards Institute (ANSI) standard document ANSI INCITS 226-1994 (S2018) (formerly X3.226-1994 (R1999) ). The Common Lisp HyperSpec , a hyperlinked HTML version, has been derived from the ANSI Common Lisp standard. The Common Lisp language was developed as a standardized and improved successor of Maclisp . By

208-434: A data type (or simply type ) is a collection or grouping of data values , usually specified by a set of possible values, a set of allowed operations on these values, and/or a representation of these values as machine types. A data type specification in a program constrains the possible values that an expression , such as a variable or a function call, might take. On literal data, it tells the compiler or interpreter how

312-402: A structured programming model would tend to not include code, and are called plain old data structures . Data types may be categorized according to several factors: The terminology varies - in the literature, primitive, built-in, basic, atomic, and fundamental may be used interchangeably. All data in computers based on digital electronics is represented as bits (alternatives 0 and 1) on

416-421: A to forall r. (forall a. f a -> r) -> r or a similar type. A refinement type is a type endowed with a predicate which is assumed to hold for any element of the refined type. For instance, the type of natural numbers greater than 5 may be written as { n ∈ N | n > 5 } {\displaystyle \{n\in \mathbb {N} \,|\,n>5\}} A dependent type

520-448: A 1988 paper by Richard P. Gabriel and Kent Pitman , which extensively compares the two approaches. Common Lisp supports the concept of multiple values , where any expression always has a single primary value , but it might also have any number of secondary values , which might be received and inspected by interested callers. This concept is distinct from returning a list value, as the secondary values are fully optional, and passed via

624-467: A binding is established at the start of the execution of some construct, such as a let block, and disappears when that construct finishes executing: its lifetime is tied to the dynamic activation and deactivation of a block. However, a dynamic binding is not just visible within that block; it is also visible to all functions invoked from that block. This type of visibility is known as indefinite scope. Bindings which exhibit dynamic extent (lifetime tied to

728-534: A collection of methods . The macro defmethod defines methods. Methods can specialize their parameters over CLOS standard classes , system classes , structure classes or individual objects. For many types, there are corresponding system classes . When a generic function is called, multiple-dispatch will determine the effective method to use. Generic Functions are also a first class data type . There are many more features to Generic Functions and Methods than described above. The namespace for function names

832-597: A corresponding native type does not exist on the target platform, the compiler will break them down into code using types that do exist. For instance, if a 32-bit integer is requested on a 16 bit platform, the compiler will tacitly treat it as an array of two 16 bit integers. Floating point data types represent certain fractional values ( rational numbers , mathematically). Although they have predefined limits on both their maximum values and their precision, they are sometimes misleadingly called reals (evocative of mathematical real numbers ). They are typically stored internally in

936-536: A decade earlier than Common Lisp, Scheme is a more minimalist design. It has a much smaller set of standard features but with certain implementation features (such as tail-call optimization and full continuations ) not specified in Common Lisp. A wide variety of programming paradigms, including imperative, functional, and message passing styles, find convenient expression in Scheme. Scheme continues to evolve with

1040-830: A dedicated side channel. This means that callers may remain entirely unaware of the secondary values being there if they have no need for them, and it makes it convenient to use the mechanism for communicating information that is sometimes useful, but not always necessary. For example, Multiple values are supported by a handful of standard forms, most common of which are the MULTIPLE-VALUE-BIND special form for accessing secondary values and VALUES for returning multiple values: Other data types in Common Lisp include: Like programs in many other programming languages, Common Lisp programs make use of names to refer to variables, functions, and many other kinds of entities. Named references are subject to scope. The association between

1144-500: A facility not available in many languages. Common Lisp automatically coerces numeric values among these types as appropriate. The Common Lisp character type is not limited to ASCII characters. Most modern implementations allow Unicode characters. The symbol type is common to Lisp languages, but largely unknown outside them. A symbol is a unique, named data object with several parts: name, value, function, property list, and package. Of these, value cell and function cell are

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1248-565: A family of function types differentiated by argument and return types, such as the type Int -> Bool denoting functions taking an integer and returning a Boolean. In C, a function is not a first-class data type but function pointers can be manipulated by the program. Java and C++ originally did not have function values but have added them in C++11 and Java 8. A type constructor builds new types from old ones, and can be thought of as an operator taking zero or more types as arguments and producing

1352-407: A flexible and powerful form of dynamic dispatch . It has served as the template for many subsequent Lisp (including Scheme ) object systems, which are often implemented via a metaobject protocol , a reflective meta-circular design in which the object system is defined in terms of itself: Lisp was only the second language after Smalltalk (and is still one of the very few languages) to possess such

1456-624: A great compliment because it transmits the full flavour of liberation: it has assisted a number of our most gifted fellow humans in thinking previously impossible thoughts. Largely because of its resource requirements with respect to early computing hardware (including early microprocessors), Lisp did not become as popular outside of the AI community as Fortran and the ALGOL -descended C language. Because of its suitability to complex and dynamic applications, Lisp enjoyed some resurgence of popular interest in

1560-460: A language others considered antiquated. New Lisp programmers often describe the language as an eye-opening experience and claim to be substantially more productive than in other languages. This increase in awareness may be contrasted to the " AI winter " and Lisp's brief gain in the mid-1990s. As of 2010 , there were eleven actively maintained Common Lisp implementations. The open source community has created new supporting infrastructure: CLiki

1664-475: A language-defined machine representation. The C programming language , for instance, supplies types such as Booleans, integers, floating-point numbers, etc., but the precise bit representations of these types are implementation-defined. The only C type with a precise machine representation is the char type that represents a byte. The Boolean type represents the values true and false . Although only two values are possible, they are more often represented as

1768-546: A list, so the expression evaluates to the list ( 1 2 foo ) . The "quote" before the foo in the preceding example is a "special operator" which returns its argument without evaluating it. Any unquoted expressions are recursively evaluated before the enclosing expression is evaluated. For example, evaluates to the list ( 1 2 ( 3 4 )) . The third argument is a list; lists can be nested. Arithmetic operators are treated similarly. The expression Data type In computer science and computer programming ,

1872-445: A metaobject system. Many years later, Alan Kay suggested that as a result of the confluence of these features, only Smalltalk and Lisp could be regarded as properly conceived object-oriented programming systems. Lisp introduced the concept of automatic garbage collection , in which the system walks the heap looking for unused memory. Progress in modern sophisticated garbage collection algorithms such as generational garbage collection

1976-455: A name and the entity which the name refers to is called a binding. Scope refers to the set of circumstances in which a name is determined to have a particular binding. The circumstances which determine scope in Common Lisp include: To understand what a symbol refers to, the Common Lisp programmer must know what kind of reference is being expressed, what kind of scope it uses if it is a variable reference (dynamic versus lexical scope), and also

2080-419: A numeric string, such as "1234" . These numeric strings are usually considered distinct from numeric values such as 1234 , although some languages automatically convert between them. A union type definition will specify which of a number of permitted subtypes may be stored in its instances, e.g. "float or long integer". In contrast with a record , which could be defined to contain a float and an integer,

2184-592: A paper in Communications of the ACM in April 1960, entitled "Recursive Functions of Symbolic Expressions and Their Computation by Machine, Part I". He showed that with a few simple operators and a notation for anonymous functions borrowed from Church, one can build a Turing-complete language for algorithms. Information Processing Language was the first AI language, from 1955 or 1956, and already included many of

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2288-617: A pointer whose value was never a valid memory address would cause a program to crash. To ameliorate this potential problem, a pointer type is typically considered distinct from the corresponding integer type, even if the underlying representation is the same. Functional programming languages treat functions as a distinct datatype and allow values of this type to be stored in variables and passed to functions. Some multi-paradigm languages such as JavaScript also have mechanisms for treating functions as data. Most contemporary type systems go beyond JavaScript's simple type "function object" and have

2392-484: A precision limited only by the available memory and computational resources on the system. Bignum implementations of arithmetic operations on machine-sized values are significantly slower than the corresponding machine operations. The enumerated type has distinct values, which can be compared and assigned, but which do not necessarily have any particular concrete representation in the computer's memory; compilers and interpreters can represent them arbitrarily. For example,

2496-409: A sequence of characters used to store words or plain text , most often textual markup languages representing formatted text . Characters may be a letter of some alphabet , a digit, a blank space, a punctuation mark, etc. Characters are drawn from a character set such as ASCII . Character and string types can have different subtypes according to the character encoding. The original 7-bit wide ASCII

2600-764: A series of standards (Revised Report on the Algorithmic Language Scheme) and a series of Scheme Requests for Implementation . Clojure is a dialect of Lisp that targets mainly the Java virtual machine , and the Common Language Runtime (CLR), the Python VM, the Ruby VM YARV , and compiling to JavaScript . It is designed to be a pragmatic general-purpose language. Clojure draws considerable influences from Haskell and places

2704-496: A single community standard Lisp dialect. Much of the initial language design was done via electronic mail. In 1982, Guy L. Steele Jr. gave the first overview of Common Lisp at the 1982 ACM Symposium on LISP and functional programming. The first language documentation was published in 1984 as Common Lisp the Language (known as CLtL1), first edition. A second edition (known as CLtL2), published in 1990, incorporated many changes to

2808-459: A single language. The new language, Common Lisp , was somewhat compatible with the dialects it replaced (the book Common Lisp the Language notes the compatibility of various constructs). In 1994, ANSI published the Common Lisp standard, "ANSI X3.226-1994 Information Technology Programming Language Common Lisp". Since inception, Lisp was closely connected with the artificial intelligence research community, especially on PDP-10 systems. Lisp

2912-526: A specific type of members, as in a vector of bits. Usually, only a few types are supported. Many implementations can optimize array functions when the array used is type-specialized. Two type-specialized array types are standard: a string is a vector of characters, while a bit-vector is a vector of bits . Hash tables store associations between data objects. Any object may be used as key or value. Hash tables are automatically resized as needed. Packages are collections of symbols, used chiefly to separate

3016-437: A standard data structure—a quality much later dubbed " homoiconicity ". Thus, Lisp functions can be manipulated, altered or even created within a Lisp program without lower-level manipulations. This is generally considered one of the main advantages of the language with regard to its expressive power, and makes the language suitable for syntactic macros and meta-circular evaluation . A conditional using an if–then–else syntax

3120-421: A type. Product types, function types, power types and list types can be made into type constructors. Universally-quantified and existentially-quantified types are based on predicate logic . Universal quantification is written as ∀ x . f ( x ) {\displaystyle \forall x.f(x)} or forall x. f x and is the intersection over all types x of the body f x , i.e.

3224-413: A union may only contain one subtype at a time. A tagged union (also called a variant , variant record, discriminated union, or disjoint union) contains an additional field indicating its current type for enhanced type safety. An algebraic data type (ADT) is a possibly recursive sum type of product types . A value of an ADT consists of a constructor tag together with zero or more field values, with

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3328-427: A very strong emphasis on immutability. Clojure provides access to Java frameworks and libraries, with optional type hints and type inference , so that calls to Java can avoid reflection and enable fast primitive operations. Clojure is not designed to be backwards compatible with other Lisp dialects. Further, Lisp dialects are used as scripting languages in many applications, with the best-known being Emacs Lisp in

3432-415: A word rather as a single bit as it requires more machine instructions to store and retrieve an individual bit. Many programming languages do not have an explicit Boolean type, instead using an integer type and interpreting (for instance) 0 as false and other values as true. Boolean data refers to the logical structure of how the language is interpreted to the machine language. In this case a Boolean 0 refers to

3536-399: Is a data structure with two slots, called its car and cdr . A list is a linked chain of conses or the empty list. Each cons's car refers to a member of the list (possibly another list). Each cons's cdr refers to the next cons—except for the last cons in a list, whose cdr refers to the nil value. Conses can also easily be used to implement trees and other complex data structures; though it

3640-544: Is a data type that does not specify the concrete representation of the data. Instead, a formal specification based on the data type's operations is used to describe it. Any implementation of a specification must fulfill the rules given. For example, a stack has push/pop operations that follow a Last-In-First-Out rule, and can be concretely implemented using either a list or an array. Abstract data types are used in formal semantics and program verification and, less strictly, in design . The main non-composite, derived type

3744-408: Is a general-purpose, multi-paradigm programming language . It supports a combination of procedural , functional , and object-oriented programming paradigms. As a dynamic programming language , it facilitates evolutionary and incremental software development , with iterative compilation into efficient run-time programs. This incremental development is often done interactively without interrupting

3848-442: Is a type whose definition depends on a value. Two common examples of dependent types are dependent functions and dependent pairs. The return type of a dependent function may depend on the value (not just type) of one of its arguments. A dependent pair may have a second value of which the type depends on the first value. An intersection type is a type containing those values that are members of two specified types. For example, in Java

3952-834: Is a weekly news service, Weekly Lisp News . Common-lisp.net is a hosting site for open source Common Lisp projects. Quicklisp is a library manager for Common Lisp. Fifty years of Lisp (1958–2008) was celebrated at LISP50@OOPSLA. There are regular local user meetings in Boston, Vancouver, and Hamburg. Other events include the European Common Lisp Meeting, the European Lisp Symposium and an International Lisp Conference. The Scheme community actively maintains over twenty implementations . Several significant new implementations (Chicken, Gambit, Gauche, Ikarus, Larceny, Ypsilon) have been developed in

4056-530: Is a wiki that collects Common Lisp related information, the Common Lisp directory lists resources, #lisp is a popular IRC channel and allows the sharing and commenting of code snippets (with support by lisppaste , an IRC bot written in Lisp), Planet Lisp collects the contents of various Lisp-related blogs, on LispForum users discuss Lisp topics, Lispjobs is a service for announcing job offers and there

4160-837: Is also possible to define a dependent intersection type, denoted ( x : σ ) ∩ τ {\displaystyle (x:\sigma )\cap \tau } , where the type τ {\displaystyle \tau } may depend on the term variable x {\displaystyle x} . Some programming languages represent the type information as data, enabling type introspection and reflection . In contrast, higher order type systems , while allowing types to be constructed from other types and passed to functions as values, typically avoid basing computational decisions on them. For convenience, high-level languages and databases may supply ready-made "real world" data types, for instance times, dates, and monetary values (currency). These may be built-in to

4264-440: Is denoted i32 and panics on overflow in debug mode. Most programming languages also allow the programmer to define additional data types, usually by combining multiple elements of other types and defining the valid operations of the new data type. For example, a programmer might create a new data type named " complex number " that would include real and imaginary parts, or a color data type represented by three bytes denoting

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4368-570: Is implemented in Femtolisp, a dialect of Scheme (Julia is inspired by Scheme, which in turn is a Lisp dialect). In October 2019, Paul Graham released a specification for Bel , "a new dialect of Lisp." Common Lisp and Scheme represent two major streams of Lisp development. These languages embody significantly different design choices. Common Lisp is a successor to Maclisp . The primary influences were Lisp Machine Lisp , Maclisp, NIL , S-1 Lisp , Spice Lisp , and Scheme. It has many of

4472-480: Is intended for reading, not for computing. But he went ahead and did it. That is, he compiled the eval in my paper into IBM 704 machine code, fixing bugs , and then advertised this as a Lisp interpreter, which it certainly was. So at that point Lisp had essentially the form that it has today ... The result was a working Lisp interpreter which could be used to run Lisp programs, or more properly, "evaluate Lisp expressions". Two assembly language macros for

4576-443: Is separate from the namespace for data variables. This is a key difference between Common Lisp and Scheme . For Common Lisp, operators that define names in the function namespace include defun , flet , labels , defmethod and defgeneric . To pass a function by name as an argument to another function, one must use the function special operator, commonly abbreviated as #' . The first sort example above refers to

4680-495: Is some conceptual overlap with structures. Objects created of classes are called Instances . A special case is Generic Functions. Generic Functions are both functions and instances. Common Lisp supports first-class functions . For instance, it is possible to write functions that take other functions as arguments or return functions as well. This makes it possible to describe very general operations. The Common Lisp library relies heavily on such higher-order functions. For example,

4784-411: Is the pointer , a data type whose value refers directly to (or "points to") another value stored elsewhere in the computer memory using its address . It is a primitive kind of reference . (In everyday terms, a page number in a book could be considered a piece of data that refers to another one). Pointers are often stored in a format similar to an integer; however, attempting to dereference or "look up"

4888-436: Is the name of a function, then the arguments a1, a2, ..., an are evaluated in left-to-right order, and the function is found and invoked with those values supplied as parameters. The macro defun defines functions where a function definition gives the name of the function, the names of any arguments, and a function body: Function definitions may include compiler directives , known as declarations , which provide hints to

4992-487: Is useful to provide anonymous functions as arguments. Local functions can be defined with flet and labels . There are several other operators related to the definition and manipulation of functions. For instance, a function may be compiled with the compile operator. (Some Lisp systems run functions using an interpreter by default unless instructed to compile; others compile every function). The macro defgeneric defines generic functions . Generic functions are

5096-447: Is usually advised to use structure or class instances instead. It is also possible to create circular data structures with conses. Common Lisp supports multidimensional arrays , and can dynamically resize adjustable arrays if required. Multidimensional arrays can be used for matrix mathematics. A vector is a one-dimensional array. Arrays can carry any type as members (even mixed types in the same array) or can be specialized to contain

5200-517: Is written as s-expressions , or parenthesized lists. A function call or syntactic form is written as a list with the function or operator's name first, and the arguments following; for instance, a function f that takes three arguments would be called as ( f arg1 arg2 arg3 ) . John McCarthy began developing Lisp in 1958 while he was at the Massachusetts Institute of Technology (MIT). McCarthy published its design in

5304-406: Is written with its elements separated by whitespace , and surrounded by parentheses. For example, ( 1 2 foo ) is a list whose elements are the three atoms 1 , 2 , and foo . These values are implicitly typed: they are respectively two integers and a Lisp-specific data type called a "symbol", and do not have to be declared as such. The empty list () is also represented as

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5408-402: The sort function takes a relational operator as an argument and key function as an optional keyword argument. This can be used not only to sort any type of data, but also to sort data structures according to a key. The evaluation model for functions is very simple. When the evaluator encounters a form (f a1 a2...) then it presumes that the symbol named f is one of the following: If f

5512-709: The Emacs editor, AutoLISP and later Visual Lisp in AutoCAD , Nyquist in Audacity , and Scheme in LilyPond . The potential small size of a useful Scheme interpreter makes it particularly popular for embedded scripting. Examples include SIOD and TinyScheme , both of which have been successfully embedded in the GIMP image processor under the generic name "Script-fu". LIBREP, a Lisp interpreter by John Harper originally based on

5616-547: The Emacs Lisp language, has been embedded in the Sawfish window manager . Lisp has officially standardized dialects: R6RS Scheme , R7RS Scheme , IEEE Scheme, ANSI Common Lisp and ISO ISLISP . Paul Graham identifies nine important aspects of Lisp that distinguished it from existing languages like Fortran : Lisp was the first language where the structure of program code is represented faithfully and directly in

5720-567: The IBM 704 became the primitive operations for decomposing lists: car ( Contents of the Address part of Register number) and cdr ( Contents of the Decrement part of Register number), where "register" refers to registers of the computer's central processing unit (CPU). Lisp dialects still use car and cdr ( / k ɑːr / and / ˈ k ʊ d ər / ) for the operations that return

5824-598: The LLVM , the Java virtual machine , x86-64, PowerPC, Alpha, ARM, Motorola 68000, and MIPS, and operating systems such as Windows, macOS, Linux, Solaris, FreeBSD, NetBSD, OpenBSD, Dragonfly BSD, and Heroku. Scheme is a statically scoped and properly tail-recursive dialect of the Lisp programming language invented by Guy L. Steele, Jr. and Gerald Jay Sussman . It was designed to have exceptionally clear and simple semantics and few different ways to form expressions. Designed about

5928-480: The Python programming language , int represents an arbitrary-precision integer which has the traditional numeric operations such as addition, subtraction, and multiplication. However, in the Java programming language , the type int represents the set of 32-bit integers ranging in value from −2,147,483,648 to 2,147,483,647, with arithmetic operations that wrap on overflow . In Rust this 32-bit integer type

6032-516: The self-hosting compiler , and the read–eval–print loop . The name LISP derives from "LISt Processor". Linked lists are one of Lisp's major data structures , and Lisp source code is made of lists. Thus, Lisp programs can manipulate source code as a data structure, giving rise to the macro systems that allow programmers to create new syntax or new domain-specific languages embedded in Lisp. The interchangeability of code and data gives Lisp its instantly recognizable syntax. All program code

6136-484: The 2000s (decade). The Revised Report on the Algorithmic Language Scheme standard of Scheme was widely accepted in the Scheme community. The Scheme Requests for Implementation process has created a lot of quasi-standard libraries and extensions for Scheme. User communities of individual Scheme implementations continue to grow. A new language standardization process was started in 2003 and led to

6240-482: The 2010s. Lisp is an expression oriented language . Unlike most other languages, no distinction is made between "expressions" and "statements" ; all code and data are written as expressions. When an expression is evaluated , it produces a value (possibly multiple values), which can then be embedded into other expressions. Each value can be any data type. McCarthy's 1958 paper introduced two types of syntax: Symbolic expressions ( S-expressions , sexps), which mirror

6344-590: The ADT corresponds to a product type similar to a tuple or record. A constructor with no fields corresponds to the empty product (unit type). If all constructors have no fields then the ADT corresponds to an enumerated type . One common ADT is the option type , defined in Haskell as data Maybe a = Nothing | Just a . Some types are very useful for storing and retrieving data and are called data structures . Common data structures include: An abstract data type

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6448-502: The Extensible Markup Language ( XML ). The reliance on expressions gives the language great flexibility. Because Lisp functions are written as lists, they can be processed exactly like data. This allows easy writing of programs which manipulate other programs ( metaprogramming ). Many Lisp dialects exploit this feature using macro systems, which enables extension of the language almost without limit. A Lisp list

6552-560: The Lisp model of incremental compilation , in which compiled and interpreted functions can intermix freely. The language used in Hart and Levin's memo is much closer to modern Lisp style than McCarthy's earlier code. Garbage collection routines were developed by MIT graduate student Daniel Edwards , prior to 1962. During the 1980s and 1990s, a great effort was made to unify the work on new Lisp dialects (mostly successors to Maclisp such as ZetaLisp and NIL (New Implementation of Lisp) into

6656-470: The R RS Scheme standard in 2007. Academic use of Scheme for teaching computer science seems to have declined somewhat. Some universities are no longer using Scheme in their computer science introductory courses; MIT now uses Python instead of Scheme for its undergraduate computer science program and MITx massive open online course. There are several new dialects of Lisp: Arc , Hy , Nu , Liskell , and LFE (Lisp Flavored Erlang). The parser for Julia

6760-462: The S-expression syntax is also responsible for much of Lisp's power: the syntax is simple and consistent, which facilitates manipulation by computer. However, the syntax of Lisp is not limited to traditional parentheses notation. It can be extended to include alternative notations. For example, XMLisp is a Common Lisp extension that employs the metaobject protocol to integrate S-expressions with

6864-781: The activation and deactivation of a block) and indefinite scope (visible to all functions which are called from that block) are said to have dynamic scope. Common Lisp has support for dynamically scoped variables, which are also called special variables. Certain other kinds of bindings are necessarily dynamically scoped also, such as restarts and catch tags. Function bindings cannot be dynamically scoped using flet (which only provides lexically scoped function bindings), but function objects (a first-level object in Common Lisp) can be assigned to dynamically scoped variables, bound using let in dynamic scope, then called using funcall or APPLY . Lisp (programming language) Lisp

6968-513: The amounts each of red, green, and blue, and a string representing the color's name. Data types are used within type systems , which offer various ways of defining, implementing, and using them. In a type system, a data type represents a constraint placed upon the interpretation of data, describing representation, interpretation and structure of values or objects stored in computer memory. The type system uses data type information to check correctness of computer programs that access or manipulate

7072-698: The argument to the nearest integer, with halfway cases rounded to the even integer. The functions truncate , floor , and ceiling round towards zero, down, or up respectively. All these functions return the discarded fractional part as a secondary value. For example, (floor -2.5) yields −3, 0.5; (ceiling -2.5) yields −2, −0.5; (round 2.5) yields 2, 0.5; and (round 3.5) yields 4, −0.5. Sequence types in Common Lisp include lists, vectors, bit-vectors, and strings. There are many operations that can work on any sequence type. As in almost all other Lisp dialects, lists in Common Lisp are composed of conses , sometimes called cons cells or pairs . A cons

7176-627: The class Boolean implements both the Serializable and the Comparable interfaces. Therefore, an object of type Boolean is a member of the type Serializable & Comparable . Considering types as sets of values, the intersection type σ ∩ τ {\displaystyle \sigma \cap \tau } is the set-theoretic intersection of σ {\displaystyle \sigma } and τ {\displaystyle \tau } . It

7280-453: The compiler about optimization settings or the data types of arguments. They may also include documentation strings (docstrings), which the Lisp system may use to provide interactive documentation: Anonymous functions ( function literals ) are defined using lambda expressions, e.g. (lambda (x) (* x x)) for a function that squares its argument. Lisp programming style frequently uses higher-order functions for which it

7384-709: The compiler can be told on a per-module or per-function basis which type of safety level is wanted, using optimize declarations. Common Lisp includes CLOS , an object system that supports multimethods and method combinations. It is often implemented with a Metaobject Protocol. Common Lisp is extensible through standard features such as Lisp macros (code transformations) and reader macros (input parsers for characters). Common Lisp provides partial backwards compatibility with Maclisp and John McCarthy's original Lisp . This allows older Lisp software to be ported to Common Lisp. Work on Common Lisp started in 1981 after an initiative by ARPA manager Bob Engelmore to develop

7488-602: The concepts, such as list-processing and recursion, which came to be used in Lisp. McCarthy's original notation used bracketed " M-expressions " that would be translated into S-expressions . As an example, the M-expression car[cons[A,B]] is equivalent to the S-expression ( car ( cons A B )) . Once Lisp was implemented, programmers rapidly chose to use S-expressions, and M-expressions were abandoned. M-expressions surfaced again with short-lived attempts of MLisp by Horace Enea and CGOL by Vaughan Pratt . Lisp

7592-418: The core theme of an S-expression language. Moreover, each given dialect may have several implementations—for instance, there are more than a dozen implementations of Common Lisp . Differences between dialects may be quite visible—for instance, Common Lisp uses the keyword defun to name a function, but Scheme uses define . Within a dialect that is standardized, however, conforming implementations support

7696-618: The data. A compiler may use the static type of a value to optimize the storage it needs and the choice of algorithms for operations on the value. In many C compilers the float data type, for example, is represented in 32 bits , in accord with the IEEE specification for single-precision floating point numbers . They will thus use floating-point-specific microprocessor operations on those values (floating-point addition, multiplication, etc.). Most data types in statistics have comparable types in computer programming, and vice versa, as shown in

7800-476: The early 1980s several groups were already at work on diverse successors to MacLisp: Lisp Machine Lisp (aka ZetaLisp), Spice Lisp , NIL and S-1 Lisp . Common Lisp sought to unify, standardise, and extend the features of these MacLisp dialects. Common Lisp is not an implementation, but rather a language specification . Several implementations of the Common Lisp standard are available, including free and open-source software and proprietary products. Common Lisp

7904-596: The features of Lisp Machine Lisp (a large Lisp dialect used to program Lisp Machines ), but was designed to be efficiently implementable on any personal computer or workstation. Common Lisp is a general-purpose programming language and thus has a large language standard including many built-in data types, functions, macros and other language elements, and an object system ( Common Lisp Object System ). Common Lisp also borrowed certain features from Scheme such as lexical scoping and lexical closures . Common Lisp implementations are available for targeting different platforms such as

8008-415: The first item in a list and the rest of the list, respectively. The first complete Lisp compiler, written in Lisp, was implemented in 1962 by Tim Hart and Mike Levin at MIT, and could be compiled by simply having an existing LISP interpreter interpret the compiler code, producing machine code output able to be executed at a 40-fold improvement in speed over that of the interpreter. This compiler introduced

8112-474: The following table: Parnas, Shore & Weiss (1976) identified five definitions of a "type" that were used—sometimes implicitly—in the literature: The definition in terms of a representation was often done in imperative languages such as ALGOL and Pascal , while the definition in terms of a value space and behaviour was used in higher-level languages such as Simula and CLU . Types including behavior align more closely with object-oriented models, whereas

8216-410: The form a × 2 (where a and b are integers), but displayed in familiar decimal form. Fixed point data types are convenient for representing monetary values. They are often implemented internally as integers, leading to predefined limits. For independence from architecture details, a Bignum or arbitrary precision numeric type might be supplied. This represents an integer or rational to

8320-422: The four suits in a deck of playing cards may be four enumerators named CLUB , DIAMOND , HEART , SPADE , belonging to an enumerated type named suit . If a variable V is declared having suit as its data type, one can assign any of those four values to it. Some implementations allow programmers to assign integer values to the enumeration values, or even treat them as type-equivalent to integers. Strings are

8424-455: The function named by the symbol > in the function namespace, with the code #'> . Conversely, to call a function passed in such a way, one would use the funcall operator on the argument. Scheme's evaluation model is simpler: there is only one namespace, and all positions in the form are evaluated (in any order) – not just the arguments. Code written in one dialect is therefore sometimes confusing to programmers more experienced in

8528-504: The internal representation of code and data; and Meta expressions ( M-expressions ), which express functions of S-expressions. M-expressions never found favor, and almost all Lisps today use S-expressions to manipulate both code and data. The use of parentheses is Lisp's most immediately obvious difference from other programming language families. As a result, students have long given Lisp nicknames such as Lost In Stupid Parentheses , or Lots of Irritating Superfluous Parentheses . However,

8632-566: The language, made during the ANSI Common Lisp standardization process: extended LOOP syntax, the Common Lisp Object System, the Condition System for error handling, an interface to the pretty printer and much more. But CLtL2 does not describe the final ANSI Common Lisp standard and thus is not a documentation of ANSI Common Lisp. The final ANSI Common Lisp standard then was published in 1994. Since then no update to

8736-475: The logic False. True is always a non zero, especially a one which is known as Boolean 1. Almost all programming languages supply one or more integer data types. They may either supply a small number of predefined subtypes restricted to certain ranges (such as short and long and their corresponding unsigned variants in C/C++); or allow users to freely define subranges such as 1..12 (e.g. Pascal / Ada ). If

8840-592: The lowest level. The smallest addressable unit of data is usually a group of bits called a byte (usually an octet , which is 8 bits). The unit processed by machine code instructions is called a word (as of 2011 , typically 32 or 64 bits). Machine data types expose or make available fine-grained control over hardware, but this can also expose implementation details that make code less portable. Hence machine types are mainly used in systems programming or low-level programming languages . In higher-level languages most data types are abstracted in that they do not have

8944-599: The most important. Symbols in Lisp are often used similarly to identifiers in other languages: to hold the value of a variable; however there are many other uses. Normally, when a symbol is evaluated, its value is returned. Some symbols evaluate to themselves, for example, all symbols in the keyword package are self-evaluating. Boolean values in Common Lisp are represented by the self-evaluating symbols T and NIL. Common Lisp has namespaces for symbols, called 'packages'. A number of functions are available for rounding scalar numeric values in various ways. The function round rounds

9048-441: The notion of data type, though the possible data types are often restricted by considerations of simplicity, computability, or regularity. An explicit data type declaration typically allows the compiler to choose an efficient machine representation, but the conceptual organization offered by data types should not be discounted. Different languages may use different data types or similar types with different semantics. For example, in

9152-400: The number and type of the field values fixed by the constructor. The set of all possible values of an ADT is the set-theoretic disjoint union (sum), of the sets of all possible values of its variants (product of fields). Values of algebraic types are analyzed with pattern matching, which identifies a value's constructor and extracts the fields it contains. If there is only one constructor, then

9256-526: The other. For instance, many Common Lisp programmers like to use descriptive variable names such as list or string which could cause problems in Scheme, as they would locally shadow function names. Whether a separate namespace for functions is an advantage is a source of contention in the Lisp community. It is usually referred to as the Lisp-1 vs. Lisp-2 debate . Lisp-1 refers to Scheme's model and Lisp-2 refers to Common Lisp's model. These names were coined in

9360-522: The parts of a program into namespaces . A package may export some symbols, marking them as part of a public interface. Packages can use other packages. Structures , similar in use to C structs and Pascal records, represent arbitrary complex data structures with any number and type of fields (called slots ). Structures allow single-inheritance. Classes are similar to structures, but offer more dynamic features and multiple-inheritance. (See CLOS ). Classes have been added late to Common Lisp and there

9464-476: The programmer intends to use the data. Most programming languages support basic data types of integer numbers (of varying sizes), floating-point numbers (which approximate real numbers ), characters and Booleans . A data type may be specified for many reasons: similarity, convenience, or to focus the attention. It is frequently a matter of good organization that aids the understanding of complex definitions. Almost all programming languages explicitly include

9568-474: The run-time situation: in what environment is the reference resolved, where was the binding introduced into the environment, et cetera. Some environments in Lisp are globally pervasive. For instance, if a new type is defined, it is known everywhere thereafter. References to that type look it up in this global environment. One type of environment in Common Lisp is the dynamic environment. Bindings established in this environment have dynamic extent, which means that

9672-430: The running application. It also supports optional type annotation and casting, which can be added as necessary at the later profiling and optimization stages, to permit the compiler to generate more efficient code. For instance, fixnum can hold an unboxed integer in a range supported by the hardware and implementation, permitting more efficient arithmetic than on big integers or arbitrary precision types. Similarly,

9776-474: The same core language, but with different extensions and libraries. After having declined somewhat in the 1990s, Lisp has experienced a resurgence of interest after 2000. Most new activity has been focused around implementations of Common Lisp , Scheme , Emacs Lisp , Clojure , and Racket , and includes development of new portable libraries and applications. Many new Lisp programmers were inspired by writers such as Paul Graham and Eric S. Raymond to pursue

9880-406: The special atom nil . This is the only entity in Lisp which is both an atom and a list. Expressions are written as lists, using prefix notation . The first element in the list is the name of a function, the name of a macro, a lambda expression or the name of a "special operator" (see below). The remainder of the list are the arguments. For example, the function list returns its arguments as

9984-684: The standard has been published. Various extensions and improvements to Common Lisp (examples are Unicode, Concurrency, CLOS-based IO) have been provided by implementations and libraries . Common Lisp is a dialect of Lisp. It uses S-expressions to denote both code and data structure. Function calls, macro forms and special forms are written as lists, with the name of the operator first, as in these examples: Common Lisp has many data types . Number types include integers , ratios , floating-point numbers , and complex numbers . Common Lisp uses bignums to represent numerical values of arbitrary size and precision. The ratio type represents fractions exactly,

10088-436: The value is of type f x for every x . Existential quantification written as ∃ x . f ( x ) {\displaystyle \exists x.f(x)} or exists x. f x and is the union over all types x of the body f x , i.e. the value is of type f x for some x . In Haskell, universal quantification is commonly used, but existential types must be encoded by transforming exists a. f

10192-404: Was first implemented by Steve Russell on an IBM 704 computer using punched cards . Russell had read McCarthy's paper and realized (to McCarthy's surprise) that the Lisp eval function could be implemented in machine code . According to McCarthy Steve Russell said, look, why don't I program this eval  ... and I said to him, ho, ho, you're confusing theory with practice, this eval

10296-400: Was found to be limited, and superseded by 8, 16 and 32-bit sets, which can encode a wide variety of non-Latin alphabets (such as Hebrew and Chinese ) and other symbols. Strings may be of either variable length or fixed length, and some programming languages have both types. They may also be subtyped by their maximum size. Since most character sets include the digits , it is possible to have

10400-420: Was influenced by Smalltalk, with later dialects adopting object-oriented programming features (inheritance classes, encapsulating instances, message passing, etc.) in the 1970s. The Flavors object system introduced the concept of multiple inheritance and the mixin . The Common Lisp Object System provides multiple inheritance, multimethods with multiple dispatch , and first-class generic functions , yielding

10504-511: Was invented by McCarthy for a chess program written in Fortran . He proposed its inclusion in ALGOL , but it was not made part of the Algol 58 specification. For Lisp, McCarthy used the more general cond -structure. Algol 60 took up if–then–else and popularized it. Lisp deeply influenced Alan Kay , the leader of the research team that developed Smalltalk at Xerox PARC ; and in turn Lisp

10608-520: Was originally created as a practical mathematical notation for computer programs , influenced by (though not originally derived from) the notation of Alonzo Church 's lambda calculus . It quickly became a favored programming language for artificial intelligence (AI) research. As one of the earliest programming languages, Lisp pioneered many ideas in computer science , including tree data structures , automatic storage management , dynamic typing , conditionals , higher-order functions , recursion ,

10712-433: Was stimulated by its use in Lisp. Edsger W. Dijkstra in his 1972 Turing Award lecture said, With a few very basic principles at its foundation, it [LISP] has shown a remarkable stability. Besides that, LISP has been the carrier for a considerable number of in a sense our most sophisticated computer applications. LISP has jokingly been described as "the most intelligent way to misuse a computer". I think that description

10816-454: Was used as the implementation of the language Micro Planner , which was used in the famous AI system SHRDLU . In the 1970s, as AI research spawned commercial offshoots, the performance of existing Lisp systems became a growing issue, as programmers needed to be familiar with the performance ramifications of the various techniques and choices involved in the implementation of Lisp. Over its sixty-year history, Lisp has spawned many variations on

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