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112-523: Lisp 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 ,

224-549: A and b denote unspecified numbers. It is believed that a notation to represent numbers was first developed at least 50,000 years ago. Early mathematical ideas such as finger counting have also been represented by collections of rocks, sticks, bone, clay, stone, wood carvings, and knotted ropes. The tally stick is a way of counting dating back to the Upper Paleolithic . Perhaps the oldest known mathematical texts are those of ancient Sumer . The Census Quipu of

336-477: A register . The binary code for this instruction is 10110 followed by a 3-bit identifier for which register to use. The identifier for the AL register is 000, so the following machine code loads the AL register with the data 01100001. This binary computer code can be made more human-readable by expressing it in hexadecimal as follows. Here, B0 means "Move a copy of the following value into AL ", and 61

448-536: 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

560-407: 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

672-623: 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

784-516: A higher-level language, for performance reasons or to interact directly with hardware in ways unsupported by the higher-level language. For instance, just under 2% of version 4.9 of the Linux kernel source code is written in assembly; more than 97% is written in C . Assembly language uses a mnemonic to represent, e.g., each low-level machine instruction or opcode , each directive , typically also each architectural register , flag , etc. Some of

896-494: A language is used to represent machine code instructions is found in Kathleen and Andrew Donald Booth 's 1947 work, Coding for A.R.C. . Assembly code is converted into executable machine code by a utility program referred to as an assembler . The term "assembler" is generally attributed to Wilkes , Wheeler and Gill in their 1951 book The Preparation of Programs for an Electronic Digital Computer , who, however, used

1008-456: 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

1120-478: A list of data, arguments or parameters. Some instructions may be "implied", which means the data upon which the instruction operates is implicitly defined by the instruction itself—such an instruction does not take an operand. The resulting statement is translated by an assembler into machine language instructions that can be loaded into memory and executed. For example, the instruction below tells an x86 / IA-32 processor to move an immediate 8-bit value into

1232-743: 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 Mathematical notation Mathematical notation consists of using symbols for representing operations , unspecified numbers , relations , and any other mathematical objects and assembling them into expressions and formulas . Mathematical notation

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1344-717: A macro definition, e.g., MEXIT in HLASM , while others may be permitted within open code (outside macro definitions), e.g., AIF and COPY in HLASM. In assembly language, the term "macro" represents a more comprehensive concept than it does in some other contexts, such as the pre-processor in the C programming language , where its #define directive typically is used to create short single line macros. Assembler macro instructions, like macros in PL/I and some other languages, can be lengthy "programs" by themselves, executed by interpretation by

1456-481: A mask of 0. Extended mnemonics are often used to support specialized uses of instructions, often for purposes not obvious from the instruction name. For example, many CPU's do not have an explicit NOP instruction, but do have instructions that can be used for the purpose. In 8086 CPUs the instruction xchg ax , ax is used for nop , with nop being a pseudo-opcode to encode the instruction xchg ax , ax . Some disassemblers recognize this and will decode

1568-444: 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

1680-438: A mnemonic is a symbolic name for a single executable machine language instruction (an opcode ), and there is at least one opcode mnemonic defined for each machine language instruction. Each instruction typically consists of an operation or opcode plus zero or more operands . Most instructions refer to a single value or a pair of values. Operands can be immediate (value coded in the instruction itself), registers specified in

1792-410: A move between a byte-sized register and either another register or memory, and the second byte, E0h, is encoded (with three bit-fields) to specify that both operands are registers, the source is AH , and the destination is AL . In a case like this where the same mnemonic can represent more than one binary instruction, the assembler determines which instruction to generate by examining the operands. In

1904-591: 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

2016-445: A particular area of mathematics. Some notations are named after their inventors, such as Leibniz's notation , Legendre symbol , Einstein's summation convention , etc. General typesetting systems are generally not well suited for mathematical notation. One of the reasons is that, in mathematical notation, the symbols are often arranged in two-dimensional figures, such as in: TeX is a mathematically oriented typesetting system that

2128-522: A programmer, so that one program can be assembled in different ways, perhaps for different applications. Or, a pseudo-op can be used to manipulate presentation of a program to make it easier to read and maintain. Another common use of pseudo-ops is to reserve storage areas for run-time data and optionally initialize their contents to known values. Symbolic assemblers let programmers associate arbitrary names ( labels or symbols ) with memory locations and various constants. Usually, every constant and variable

2240-400: A pseudoinstruction that expands to the machine's "set if less than" and "branch if zero (on the result of the set instruction)". Most full-featured assemblers also provide a rich macro language (discussed below) which is used by vendors and programmers to generate more complex code and data sequences. Since the information about pseudoinstructions and macros defined in the assembler environment

2352-400: A second pass would require storing the symbol table in memory (to handle forward references ), rewinding and rereading the program source on tape , or rereading a deck of cards or punched paper tape . Later computers with much larger memories (especially disc storage), had the space to perform all necessary processing without such re-reading. The advantage of the multi-pass assembler is that

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2464-846: A sentence. Letters are typically used for naming—in mathematical jargon , one says representing — mathematical objects . The Latin and Greek alphabets are used extensively, but a few letters of other alphabets are also used sporadically, such as the Hebrew ⁠ ℵ {\displaystyle \aleph } ⁠ , Cyrillic Ш , and Hiragana よ . Uppercase and lowercase letters are considered as different symbols. For Latin alphabet, different typefaces also provide different symbols. For example, r , R , R , R , r , {\displaystyle r,R,\mathbb {R} ,{\mathcal {R}},{\mathfrak {r}},} and R {\displaystyle {\mathfrak {R}}} could theoretically appear in

2576-763: 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

2688-514: 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

2800-437: 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

2912-425: 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

3024-403: Is a one-to-one correspondence between many simple assembly statements and machine language instructions. However, in some cases, an assembler may provide pseudoinstructions (essentially macros) which expand into several machine language instructions to provide commonly needed functionality. For example, for a machine that lacks a "branch if greater or equal" instruction, an assembler may provide

3136-462: Is a finite combination of symbols that is well-formed according to rules that depend on the context. In general, an expression denotes or names a mathematical object , and plays therefore in the language of mathematics the role of a noun phrase in the natural language. An expression contains often some operators , and may therefore be evaluated by the action of the operators in it. For example, 3 + 2 {\displaystyle 3+2}

3248-447: Is a hexadecimal representation of the value 01100001, which is 97 in decimal . Assembly language for the 8086 family provides the mnemonic MOV (an abbreviation of move ) for instructions such as this, so the machine code above can be written as follows in assembly language, complete with an explanatory comment if required, after the semicolon. This is much easier to read and to remember. In some assembly languages (including this one)

3360-453: Is a key feature of assemblers, saving tedious calculations and manual address updates after program modifications. Most assemblers also include macro facilities for performing textual substitution – e.g., to generate common short sequences of instructions as inline , instead of called subroutines . Some assemblers may also be able to perform some simple types of instruction set -specific optimizations . One concrete example of this may be

3472-832: 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

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3584-527: 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

3696-404: Is always completely unable to recover source comments. Each computer architecture has its own machine language. Computers differ in the number and type of operations they support, in the different sizes and numbers of registers, and in the representations of data in storage. While most general-purpose computers are able to carry out essentially the same functionality, the ways they do so differ;

3808-482: Is an expression in which the operator + {\displaystyle +} can be evaluated for giving the result 5. {\displaystyle 5.} So, 3 + 2 {\displaystyle 3+2} and 5 {\displaystyle 5} are two different expressions that represent the same number. This is the meaning of the equality 3 + 2 = 5. {\displaystyle 3+2=5.} A more complicated example

3920-442: Is any low-level programming language with a very strong correspondence between the instructions in the language and the architecture's machine code instructions . Assembly language usually has one statement per machine instruction (1:1), but constants, comments , assembler directives , symbolic labels of, e.g., memory locations , registers , and macros are generally also supported. The first assembly code in which

4032-625: Is based mostly on the Arabic alphabet and is used widely in the Arab world , especially in pre- tertiary education . (Western notation uses Arabic numerals , but the Arabic notation also replaces Latin letters and related symbols with Arabic script.) In addition to Arabic notation, mathematics also makes use of Greek letters to denote a wide variety of mathematical objects and variables. On some occasions, certain Hebrew letters are also used (such as in

4144-508: Is essential in assembly language programs, as the meaning and purpose of a sequence of binary machine instructions can be difficult to determine. The "raw" (uncommented) assembly language generated by compilers or disassemblers is quite difficult to read when changes must be made. Many assemblers support predefined macros , and others support programmer-defined (and repeatedly re-definable) macros involving sequences of text lines in which variables and constants are embedded. The macro definition

4256-401: Is given a name so instructions can reference those locations by name, thus promoting self-documenting code . In executable code, the name of each subroutine is associated with its entry point, so any calls to a subroutine can use its name. Inside subroutines, GOTO destinations are given labels. Some assemblers support local symbols which are often lexically distinct from normal symbols (e.g.,

4368-455: Is given by the expression ∫ a b x d x {\textstyle \int _{a}^{b}xdx} that can be evaluated to b 2 2 − a 2 2 . {\textstyle {\frac {b^{2}}{2}}-{\frac {a^{2}}{2}}.} Although the resulting expression contains the operators of division , subtraction and exponentiation , it cannot be evaluated further because

4480-569: 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

4592-480: 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

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4704-679: Is more than one assembler for the same architecture, and sometimes an assembler is specific to an operating system or to particular operating systems. Most assembly languages do not provide specific syntax for operating system calls, and most assembly languages can be used universally with any operating system, as the language provides access to all the real capabilities of the processor , upon which all system call mechanisms ultimately rest. In contrast to assembly languages, most high-level programming languages are generally portable across multiple architectures but require interpreting or compiling , much more complicated tasks than assembling. In

4816-442: Is most commonly a mixture of assembler statements, e.g., directives, symbolic machine instructions, and templates for assembler statements. This sequence of text lines may include opcodes or directives. Once a macro has been defined its name may be used in place of a mnemonic. When the assembler processes such a statement, it replaces the statement with the text lines associated with that macro, then processes them as if they existed in

4928-407: Is not present in the object program, a disassembler cannot reconstruct the macro and pseudoinstruction invocations but can only disassemble the actual machine instructions that the assembler generated from those abstract assembly-language entities. Likewise, since comments in the assembly language source file are ignored by the assembler and have no effect on the object code it generates, a disassembler

5040-524: Is universally enforced by their syntax. For example, in the Intel x86 assembly language, a hexadecimal constant must start with a numeral digit, so that the hexadecimal number 'A' (equal to decimal ten) would be written as 0Ah or 0AH , not AH , specifically so that it cannot appear to be the name of register AH . (The same rule also prevents ambiguity with the names of registers BH , CH , and DH , as well as with any user-defined symbol that ends with

5152-412: Is widely used in mathematics , science , and engineering for representing complex concepts and properties in a concise, unambiguous, and accurate way. For example, the physicist Albert Einstein 's formula E = m c 2 {\displaystyle E=mc^{2}} is the quantitative representation in mathematical notation of mass–energy equivalence . Mathematical notation

5264-517: 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

5376-406: 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

5488-476: The xchg ax , ax instruction as nop . Similarly, IBM assemblers for System/360 and System/370 use the extended mnemonics NOP and NOPR for BC and BCR with zero masks. For the SPARC architecture, these are known as synthetic instructions . Some assemblers also support simple built-in macro-instructions that generate two or more machine instructions. For instance, with some Z80 assemblers

5600-471: The CPU pipeline as efficiently as possible. Assemblers have been available since the 1950s, as the first step above machine language and before high-level programming languages such as Fortran , Algol , COBOL and Lisp . There have also been several classes of translators and semi-automatic code generators with properties similar to both assembly and high-level languages, with Speedcode as perhaps one of

5712-708: 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

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5824-544: 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

5936-1177: The Fourier transform of the derivative of a function called f 1 . {\displaystyle f_{1}.} Symbols are not only used for naming mathematical objects. They can be used for operations ( + , − , / , ⊕ , … ) , {\displaystyle (+,-,/,\oplus ,\ldots ),} for relations ( = , < , ≤ , ∼ , ≡ , … ) , {\displaystyle (=,<,\leq ,\sim ,\equiv ,\ldots ),} for logical connectives ( ⟹ , ∧ , ∨ , … ) , {\displaystyle (\implies ,\land ,\lor ,\ldots ),} for quantifiers ( ∀ , ∃ ) , {\displaystyle (\forall ,\exists ),} and for other purposes. Some symbols are similar to Latin or Greek letters, some are obtained by deforming letters, some are traditional typographic symbols , but many have been specially designed for mathematics. An expression

6048-566: 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

6160-594: 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

6272-513: 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

6384-756: The 1950s and early 1960s. Some assemblers have free-form syntax, with fields separated by delimiters, e.g., punctuation, white space . Some assemblers are hybrid, with, e.g., labels, in a specific column and other fields separated by delimiters; this became more common than column-oriented syntax in the 1960s. An assembler program creates object code by translating combinations of mnemonics and syntax for operations and addressing modes into their numerical equivalents. This representation typically includes an operation code (" opcode ") as well as other control bits and data. The assembler also calculates constant expressions and resolves symbolic names for memory locations and other entities. The use of symbolic references

6496-482: 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

6608-480: 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

6720-658: The Andes and the Ishango Bone from Africa both used the tally mark method of accounting for numerical concepts. The concept of zero and the introduction of a notation for it are important developments in early mathematics, which predates for centuries the concept of zero as a number. It was used as a placeholder by the Babylonians and Greek Egyptians , and then as an integer by the Mayans , Indians and Arabs (see

6832-502: 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

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6944-544: The Intel 8080 family and the Intel 8086/8088. Because Intel claimed copyright on its assembly language mnemonics (on each page of their documentation published in the 1970s and early 1980s, at least), some companies that independently produced CPUs compatible with Intel instruction sets invented their own mnemonics. The Zilog Z80 CPU, an enhancement of the Intel 8080A , supports all the 8080A instructions plus many more; Zilog invented an entirely new assembly language, not only for

7056-559: 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

7168-524: The RRS 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

7280-462: 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

7392-527: The V20 and V30 actually wrote in NEC's assembly language rather than Intel's; since any two assembly languages for the same instruction set architecture are isomorphic (somewhat like English and Pig Latin ), there is no requirement to use a manufacturer's own published assembly language with that manufacturer's products. There is a large degree of diversity in the way the authors of assemblers categorize statements and in

7504-463: The Z80, NEC invented new mnemonics for all of the 8086 and 8088 instructions, to avoid accusations of infringement of Intel's copyright. (It is questionable whether such copyrights can be valid, and later CPU companies such as AMD and Cyrix republished Intel's x86/IA-32 instruction mnemonics exactly with neither permission nor legal penalty.) It is doubtful whether in practice many people who programmed

7616-402: The absence of errata makes the linking process (or the program load if the assembler directly produces executable code) faster. Example: in the following code snippet, a one-pass assembler would be able to determine the address of the backward reference BKWD when assembling statement S2 , but would not be able to determine the address of the forward reference FWD when assembling

7728-424: The architecture, these elements may also be combined for specific instructions or addressing modes using offsets or other data as well as fixed addresses. Many assemblers offer additional mechanisms to facilitate program development, to control the assembly process, and to aid debugging . Some are column oriented, with specific fields in specific columns; this was very common for machines using punched cards in

7840-443: The assembler operates and "may affect the object code, the symbol table, the listing file, and the values of internal assembler parameters". Sometimes the term pseudo-opcode is reserved for directives that generate object code, such as those that generate data. The names of pseudo-ops often start with a dot to distinguish them from machine instructions. Pseudo-ops can make the assembly of the program dependent on parameters input by

7952-586: The better-known examples. There may be several assemblers with different syntax for a particular CPU or instruction set architecture . For instance, an instruction to add memory data to a register in a x86 -family processor might be add eax,[ebx] , in original Intel syntax , whereas this would be written addl (%ebx),%eax in the AT&;T syntax used by the GNU Assembler . Despite different appearances, different syntactic forms generally generate

8064-674: The branch statement S1 ; indeed, FWD may be undefined. A two-pass assembler would determine both addresses in pass 1, so they would be known when generating code in pass 2. More sophisticated high-level assemblers provide language abstractions such as: See Language design below for more details. A program written in assembly language consists of a series of mnemonic processor instructions and meta-statements (known variously as declarative operations, directives, pseudo-instructions, pseudo-operations and pseudo-ops), comments and data. Assembly language instructions usually consist of an opcode mnemonic followed by an operand , which might be

8176-601: 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

8288-555: The context of infinite cardinals ). Some mathematical notations are mostly diagrammatic, and so are almost entirely script independent. Examples are Penrose graphical notation and Coxeter–Dynkin diagrams . Braille-based mathematical notations used by blind people include Nemeth Braille and GS8 Braille . Assembly language macros In computer programming , assembly language (alternatively assembler language or symbolic machine code ), often referred to simply as assembly and commonly abbreviated as ASM or asm ,

8400-417: 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

8512-453: The corresponding assembly languages reflect these differences. Multiple sets of mnemonics or assembly-language syntax may exist for a single instruction set, typically instantiated in different assembler programs. In these cases, the most popular one is usually that supplied by the CPU manufacturer and used in its documentation. Two examples of CPUs that have two different sets of mnemonics are

8624-596: 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

8736-425: The first decades of computing, it was commonplace for both systems programming and application programming to take place entirely in assembly language. While still irreplaceable for some purposes, the majority of programming is now conducted in higher-level interpreted and compiled languages. In " No Silver Bullet ", Fred Brooks summarised the effects of the switch away from assembly language programming: "Surely

8848-480: The first example, the operand 61h is a valid hexadecimal numeric constant and is not a valid register name, so only the B0 instruction can be applicable. In the second example, the operand AH is a valid register name and not a valid numeric constant (hexadecimal, decimal, octal, or binary), so only the 88 instruction can be applicable. Assembly languages are always designed so that this sort of lack of ambiguity

8960-414: 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

9072-467: The following examples show. In each case, the MOV mnemonic is translated directly into one of the opcodes 88-8C, 8E, A0-A3, B0-BF, C6 or C7 by an assembler, and the programmer normally does not have to know or remember which. Transforming assembly language into machine code is the job of an assembler, and the reverse can at least partially be achieved by a disassembler . Unlike high-level languages , there

9184-541: The history of zero ). Until the 16th century, mathematics was essentially rhetorical , in the sense that everything but explicit numbers was expressed in words. However, some authors such as Diophantus used some symbols as abbreviations. The first systematic use of formulas, and, in particular the use of symbols ( variables ) for unspecified numbers is generally attributed to François Viète (16th century). However, he used different symbols than those that are now standard. Later, René Descartes (17th century) introduced

9296-459: The instruction ld hl,bc is recognized to generate ld l,c followed by ld h,b . These are sometimes known as pseudo-opcodes . Mnemonics are arbitrary symbols; in 1985 the IEEE published Standard 694 for a uniform set of mnemonics to be used by all assemblers. The standard has since been withdrawn. There are instructions used to define data elements to hold data and variables. They define

9408-526: The instruction or implied, or the addresses of data located elsewhere in storage. This is determined by the underlying processor architecture: the assembler merely reflects how this architecture works. Extended mnemonics are often used to specify a combination of an opcode with a specific operand, e.g., the System/360 assemblers use B as an extended mnemonic for BC with a mask of 15 and NOP ("NO OPeration" – do nothing for one step) for BC with

9520-503: 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,

9632-403: The letter H and otherwise contains only characters that are hexadecimal digits, such as the word "BEACH".) Returning to the original example, while the x86 opcode 10110000 ( B0 ) copies an 8-bit value into the AL register, 10110001 ( B1 ) moves it into CL and 10110010 ( B2 ) does so into DL . Assembly language examples for these follow. The syntax of MOV can also be more complex as

9744-427: The mnemonics may be built-in and some user-defined. Many operations require one or more operands in order to form a complete instruction. Most assemblers permit named constants, registers, and labels for program and memory locations, and can calculate expressions for operands. Thus, programmers are freed from tedious repetitive calculations and assembler programs are much more readable than machine code. Depending on

9856-472: The modern notation for variables and equations ; in particular, the use of x , y , z {\displaystyle x,y,z} for unknown quantities and a , b , c {\displaystyle a,b,c} for known ones ( constants ). He introduced also the notation i and the term "imaginary" for the imaginary unit . The 18th and 19th centuries saw the standardization of mathematical notation as used today. Leonhard Euler

9968-423: The most powerful stroke for software productivity, reliability, and simplicity has been the progressive use of high-level languages for programming. Most observers credit that development with at least a factor of five in productivity, and with concomitant gains in reliability, simplicity, and comprehensibility." Today, it is typical to use small amounts of assembly language code within larger systems implemented in

10080-463: The new instructions but also for all of the 8080A instructions. For example, where Intel uses the mnemonics MOV , MVI , LDA , STA , LXI , LDAX , STAX , LHLD , and SHLD for various data transfer instructions, the Z80 assembly language uses the mnemonic LD for all of them. A similar case is the NEC V20 and V30 CPUs, enhanced copies of the Intel 8086 and 8088, respectively. Like Zilog with

10192-400: The nomenclature that they use. In particular, some describe anything other than a machine mnemonic or extended mnemonic as a pseudo-operation (pseudo-op). A typical assembly language consists of 3 types of instruction statements that are used to define program operations: Instructions (statements) in assembly language are generally very simple, unlike those in high-level languages . Generally,

10304-405: The operation, and if necessary, pad it with one or more " no-operation " instructions in a later pass or the errata. In an assembler with peephole optimization , addresses may be recalculated between passes to allow replacing pessimistic code with code tailored to the exact distance from the target. The original reason for the use of one-pass assemblers was memory size and speed of assembly – often

10416-474: 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

10528-577: The same mathematical text with six different meanings. Normally, roman upright typeface is not used for symbols, except for symbols representing a standard function, such as the symbol " sin {\displaystyle \sin } " of the sine function . In order to have more symbols, and for allowing related mathematical objects to be represented by related symbols, diacritics , subscripts and superscripts are often used. For example, f 1 ′ ^ {\displaystyle {\hat {f'_{1}}}} may denote

10640-499: The same mnemonic is used for different instructions, that means that the mnemonic corresponds to several different binary instruction codes, excluding data (e.g. the 61h in this example), depending on the operands that follow the mnemonic. For example, for the x86/IA-32 CPUs, the Intel assembly language syntax MOV AL, AH represents an instruction that moves the contents of register AH into register AL . The hexadecimal form of this instruction is: The first byte, 88h, identifies

10752-489: The same mnemonic, such as MOV, may be used for a family of related instructions for loading, copying and moving data, whether these are immediate values, values in registers, or memory locations pointed to by values in registers or by immediate (a.k.a. direct) addresses. Other assemblers may use separate opcode mnemonics such as L for "move memory to register", ST for "move register to memory", LR for "move register to register", MVI for "move immediate operand to memory", etc. If

10864-415: The same numeric machine code . A single assembler may also have different modes in order to support variations in syntactic forms as well as their exact semantic interpretations (such as FASM -syntax, TASM -syntax, ideal mode, etc., in the special case of x86 assembly programming). There are two types of assemblers based on how many passes through the source are needed (how many times the assembler reads

10976-433: The source code file (including, in some assemblers, expansion of any macros existing in the replacement text). Macros in this sense date to IBM autocoders of the 1950s. Macro assemblers typically have directives to, e.g., define macros, define variables, set variables to the result of an arithmetic, logical or string expression, iterate, conditionally generate code. Some of those directives may be restricted to use within

11088-407: The source) to produce the object file. In both cases, the assembler must be able to determine the size of each instruction on the initial passes in order to calculate the addresses of subsequent symbols. This means that if the size of an operation referring to an operand defined later depends on the type or distance of the operand, the assembler will make a pessimistic estimate when first encountering

11200-406: 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

11312-456: The term to mean "a program that assembles another program consisting of several sections into a single program". The conversion process is referred to as assembly , as in assembling the source code . The computational step when an assembler is processing a program is called assembly time . Because assembly depends on the machine code instructions, each assembly language is specific to a particular computer architecture . Sometimes there

11424-496: The type of data, the length and the alignment of data. These instructions can also define whether the data is available to outside programs (programs assembled separately) or only to the program in which the data section is defined. Some assemblers classify these as pseudo-ops. Assembly directives, also called pseudo-opcodes, pseudo-operations or pseudo-ops, are commands given to an assembler "directing it to perform operations other than assembling instructions". Directives affect how

11536-414: The ubiquitous x86 assemblers from various vendors. Called jump-sizing , most of them are able to perform jump-instruction replacements (long jumps replaced by short or relative jumps) in any number of passes, on request. Others may even do simple rearrangement or insertion of instructions, such as some assemblers for RISC architectures that can help optimize a sensible instruction scheduling to exploit

11648-591: The use of "10$ " as a GOTO destination). Some assemblers, such as NASM , provide flexible symbol management, letting programmers manage different namespaces , automatically calculate offsets within data structures , and assign labels that refer to literal values or the result of simple computations performed by the assembler. Labels can also be used to initialize constants and variables with relocatable addresses. Assembly languages, like most other computer languages, allow comments to be added to program source code that will be ignored during assembly. Judicious commenting

11760-708: Was created in 1978 by Donald Knuth . It is widely used in mathematics, through its extension called LaTeX , and is a de facto standard. (The above expression is written in LaTeX.) More recently, another approach for mathematical typesetting is provided by MathML . However, it is not well supported in web browsers, which is its primary target. The international standard ISO 80000-2 (previously, ISO 31-11 ) specifies symbols for use in mathematical equations. The standard requires use of italic fonts for variables (e.g., E = mc ) and roman (upright) fonts for mathematical constants (e.g., e or π). Modern Arabic mathematical notation

11872-402: 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

11984-465: Was first introduced by François Viète at the end of the 16th century and largely expanded during the 17th and 18th centuries by René Descartes , Isaac Newton , Gottfried Wilhelm Leibniz , and overall Leonhard Euler . The use of many symbols is the basis of mathematical notation. They play a similar role as words in natural languages . They may play different roles in mathematical notation similarly as verbs, adjective and nouns play different roles in

12096-420: 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

12208-510: 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

12320-557: Was responsible for many of the notations currently in use: the functional notation f ( x ) , {\displaystyle f(x),} e for the base of the natural logarithm, ∑ {\textstyle \sum } for summation , etc. He also popularized the use of π for the Archimedes constant (proposed by William Jones , based on an earlier notation of William Oughtred ). Since then many new notations have been introduced, often specific to

12432-432: 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

12544-453: 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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