In computer science , an interpreter is a computer program that directly executes instructions written in a programming or scripting language , without requiring them previously to have been compiled into a machine language program. An interpreter generally uses one of the following strategies for program execution:
115-783: Early versions of Lisp programming language and minicomputer and microcomputer BASIC dialects would be examples of the first type. Perl , Raku , Python , MATLAB , and Ruby are examples of the second, while UCSD Pascal is an example of the third type. Source programs are compiled ahead of time and stored as machine independent code, which is then linked at run-time and executed by an interpreter and/or compiler (for JIT systems). Some systems, such as Smalltalk and contemporary versions of BASIC and Java , may also combine two and three types. Interpreters of various types have also been constructed for many languages traditionally associated with compilation, such as Algol , Fortran , Cobol , C and C++ . While interpretation and compilation are
230-481: A garbage collector and debugger . Programs written in a high-level language are either directly executed by some kind of interpreter or converted into machine code by a compiler (and assembler and linker ) for the CPU to execute. While compilers (and assemblers) generally produce machine code directly executable by computer hardware, they can often (optionally) produce an intermediate form called object code . This
345-468: A variable-length code requiring 3, 6, 10, or 18 bits, and address operands include a "bit offset". Many BASIC interpreters can store and read back their own tokenized internal representation. An interpreter might well use the same lexical analyzer and parser as the compiler and then interpret the resulting abstract syntax tree . Example data type definitions for the latter, and a toy interpreter for syntax trees obtained from C expressions are shown in
460-464: A virtual machine , which is implemented not in hardware, but in the bytecode interpreter. Such compiling interpreters are sometimes also called compreters . In a bytecode interpreter each instruction starts with a byte, and therefore bytecode interpreters have up to 256 instructions, although not all may be used. Some bytecodes may take multiple bytes, and may be arbitrarily complicated. Control tables - that do not necessarily ever need to pass through
575-440: A bytecode interpreter, because of nodes related to syntax performing no useful work, of a less sequential representation (requiring traversal of more pointers) and of overhead visiting the tree. Further blurring the distinction between interpreters, bytecode interpreters and compilation is just-in-time (JIT) compilation, a technique in which the intermediate representation is compiled to native machine code at runtime. This confers
690-413: A compiler works. However, a compiled program still runs much faster, under most circumstances, in part because compilers are designed to optimize code, and may be given ample time for this. This is especially true for simpler high-level languages without (many) dynamic data structures, checks, or type checking . In traditional compilation, the executable output of the linkers (.exe files or .dll files or
805-439: A compiling phase - dictate appropriate algorithmic control flow via customized interpreters in similar fashion to bytecode interpreters. Threaded code interpreters are similar to bytecode interpreters but instead of bytes they use pointers. Each "instruction" is a word that points to a function or an instruction sequence, possibly followed by a parameter. The threaded code interpreter either loops fetching instructions and calling
920-413: A computer language is usually done in relation to an abstract machine (so-called operational semantics ) or as a mathematical function ( denotational semantics ). A language may also be defined by an interpreter in which the semantics of the host language is given. The definition of a language by a self-interpreter is not well-founded (it cannot define a language), but a self-interpreter tells a reader about
1035-526: 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
1150-452: A few seconds to a few minutes. A replacement garbage collector for Applesoft BASIC by Randy Wigginton identifies a group of strings in every pass over the heap, reducing collection time dramatically. BASIC.SYSTEM, released with ProDOS in 1983, provides a windowing garbage collector for BASIC that is many times faster. While the Objective-C traditionally had no garbage collection, with
1265-407: 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
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#17331161040551380-617: 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
1495-460: 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
1610-412: A large number of algorithms used in implementation, with widely varying complexity and performance characteristics. Reference counting garbage collection is where each object has a count of the number of references to it. Garbage is identified by having a reference count of zero. An object's reference count is incremented when a reference to it is created and decremented when a reference is destroyed. When
1725-941: A library, as with the Boehm garbage collector for C and C++. Most functional programming languages , such as ML , Haskell , and APL , have garbage collection built in. Lisp is especially notable as both the first functional programming language and the first language to introduce garbage collection. Other dynamic languages, such as Ruby and Julia (but not Perl 5 or PHP before version 5.3, which both use reference counting), JavaScript and ECMAScript also tend to use GC. Object-oriented programming languages such as Smalltalk , ooRexx , RPL and Java usually provide integrated garbage collection. Notable exceptions are C++ and Delphi , which have destructors . BASIC and Logo have often used garbage collection for variable-length data types, such as strings and lists, so as not to burden programmers with memory management details. On
1840-418: A library, see picture) is typically relocatable when run under a general operating system, much like the object code modules are but with the difference that this relocation is done dynamically at run time, i.e. when the program is loaded for execution. On the other hand, compiled and linked programs for small embedded systems are typically statically allocated, often hard coded in a NOR flash memory, as there
1955-710: A list of these commands in the order a programmer wishes to execute them. Each command (also known as an Instruction ) contains the data the programmer wants to mutate, and information on how to mutate the data. For example, an interpreter might read ADD Books, 5 and interpret it as a request to add five to the Books variable . Interpreters have a wide variety of instructions which are specialized to perform different tasks, but you will commonly find interpreter instructions for basic mathematical operations , branching , and memory management , making most interpreters Turing complete . Many interpreters are also closely integrated with
2070-578: 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 Garbage collection (computer science) In computer science , garbage collection ( GC )
2185-445: 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
2300-425: A number of disadvantages to reference counting; this can generally be solved or mitigated by more sophisticated algorithms: Escape analysis is a compile-time technique that can convert heap allocations to stack allocations , thereby reducing the amount of garbage collection to be done. This analysis determines whether an object allocated inside a function is accessible outside of it. If a function-local allocation
2415-578: 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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#17331161040552530-439: A parse tree, and both may generate immediate instructions (for a stack machine , quadruple code , or by other means). The basic difference is that a compiler system, including a (built in or separate) linker, generates a stand-alone machine code program, while an interpreter system instead performs the actions described by the high-level program. A compiler can thus make almost all the conversions from source code semantics to
2645-728: 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
2760-404: A similar effect to obfuscation, but bytecode could be decoded with a decompiler or disassembler . The main disadvantage of interpreters is that an interpreted program typically runs more slowly than if it had been compiled . The difference in speeds could be tiny or great; often an order of magnitude and sometimes more. It generally takes longer to run a program under an interpreter than to run
2875-510: 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
2990-437: 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
3105-494: A suitable interpreter. If the interpreter needs to be supplied along with the source, the overall installation process is more complex than delivery of a monolithic executable, since the interpreter itself is part of what needs to be installed. The fact that interpreted code can easily be read and copied by humans can be of concern from the point of view of copyright . However, various systems of encryption and obfuscation exist. Delivery of intermediate code, such as bytecode, has
3220-472: A template interpreter. Rather than implement the execution of code by virtue of a large switch statement containing every possible bytecode, while operating on a software stack or a tree walk, a template interpreter maintains a large array of bytecode (or any efficient intermediate representation) mapped directly to corresponding native machine instructions that can be executed on the host hardware as key value pairs (or in more efficient designs, direct addresses to
3335-427: 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
3450-415: A wide range of computational tasks, including binary emulation and internet applications. Interpreter performance is still a worry despite their adaptability, particularly on systems with limited hardware resources. Advanced instrumentation and tracing approaches provide insights into interpreter implementations and processor resource utilization during execution through evaluations of interpreters tailored for
3565-463: Is a family of programming languages with a long history and a distinctive, fully parenthesized prefix notation . Originally specified in the late 1950s, it is the second-oldest high-level programming language still in common use, after Fortran . Lisp has changed since its early days, and many dialects have existed over its history. Today, the best-known general-purpose Lisp dialects are Common Lisp , Scheme , Racket , and Clojure . Lisp
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3680-430: Is a few decades old, appearing in languages such as Smalltalk in the 1980s. Just-in-time compilation has gained mainstream attention amongst language implementers in recent years, with Java , the .NET Framework , most modern JavaScript implementations, and Matlab now including JIT compilers. Making the distinction between compilers and interpreters yet again even more vague is a special interpreter design known as
3795-572: Is a form of static analysis allowing memory to be reused and reclaimed based on invariants known during compilation. This form of garbage collection has been studied in the Mercury programming language , and it saw greater usage with the introduction of LLVM 's automatic reference counter (ARC) into Apple's ecosystem (iOS and OS X) in 2011. Incremental, concurrent, and real-time garbage collectors have been developed, for example by Henry Baker and by Henry Lieberman . In Baker's algorithm,
3910-470: Is a form of automatic memory management . The garbage collector attempts to reclaim memory that was allocated by the program, but is no longer referenced; such memory is called garbage . Garbage collection was invented by American computer scientist John McCarthy around 1959 to simplify manual memory management in Lisp . Garbage collection relieves the programmer from doing manual memory management , where
4025-688: Is a layer of hardware-level instructions that implement higher-level machine code instructions or internal state machine sequencing in many digital processing elements. Microcode is used in general-purpose central processing units , as well as in more specialized processors such as microcontrollers , digital signal processors , channel controllers , disk controllers , network interface controllers , network processors , graphics processing units , and in other hardware. Microcode typically resides in special high-speed memory and translates machine instructions, state machine data or other input into sequences of detailed circuit-level operations. It separates
4140-532: Is a relatively simple way to achieve software compatibility between different products in a processor family. Even a non microcoding computer processor itself can be considered to be a parsing immediate execution interpreter that is written in a general purpose hardware description language such as VHDL to create a system that parses the machine code instructions and immediately executes them. Interpreters, such as those written in Java, Perl, and Tcl, are now necessary for
4255-808: 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
4370-520: 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
4485-583: Is basically the same machine specific code but augmented with a symbol table with names and tags to make executable blocks (or modules) identifiable and relocatable. Compiled programs will typically use building blocks (functions) kept in a library of such object code modules. A linker is used to combine (pre-made) library files with the object file(s) of the application to form a single executable file. The object files that are used to generate an executable file are thus often produced at different times, and sometimes even by different languages (capable of generating
4600-437: Is compiled into "F code" (a bytecode), which is then interpreted by a virtual machine . In the spectrum between interpreting and compiling, another approach is to transform the source code into an optimized abstract syntax tree (AST), then execute the program following this tree structure, or use it to generate native code just-in-time . In this approach, each sentence needs to be parsed just once. As an advantage over bytecode,
4715-431: Is executed and then perform the desired action, whereas the compiled code just performs the action within a fixed context determined by the compilation. This run-time analysis is known as "interpretive overhead". Access to variables is also slower in an interpreter because the mapping of identifiers to storage locations must be done repeatedly at run-time rather than at compile time . There are various compromises between
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4830-489: Is found to be accessible to another function or thread, the allocation is said to "escape" and cannot be done on the stack. Otherwise, the object may be allocated directly on the stack and released when the function returns, bypassing the heap and associated memory management costs. Generally speaking, higher-level programming languages are more likely to have garbage collection as a standard feature. In some languages lacking built-in garbage collection, it can be added through
4945-565: 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
5060-430: Is implemented using closures in the interpreter language or implemented "manually" with a data structure explicitly storing the environment. The more features implemented by the same feature in the host language, the less control the programmer of the interpreter has; for example, a different behavior for dealing with number overflows cannot be realized if the arithmetic operations are delegated to corresponding operations in
5175-480: 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
5290-542: Is more difficult to maintain due to the interpreter having to support translation to multiple different architectures instead of a platform independent virtual machine/stack. To date, the only template interpreter implementations of widely known languages to exist are the interpreter within Java's official reference implementation, the Sun HotSpot Java Virtual Machine, and the Ignition Interpreter in
5405-449: Is often no secondary storage and no operating system in this sense. Historically, most interpreter systems have had a self-contained editor built in. This is becoming more common also for compilers (then often called an IDE ), although some programmers prefer to use an editor of their choice and run the compiler, linker and other tools manually. Historically, compilers predate interpreters because hardware at that time could not support both
5520-486: Is such a language, because XSLT programs are written in XML. A sub-domain of metaprogramming is the writing of domain-specific languages (DSLs). Clive Gifford introduced a measure quality of self-interpreter (the eigenratio), the limit of the ratio between computer time spent running a stack of N self-interpreters and time spent to run a stack of N − 1 self-interpreters as N goes to infinity. This value does not depend on
5635-439: Is the most common type of garbage collection, so much so that "garbage collection" often refers to tracing garbage collection, rather than other methods such as reference counting . The overall strategy consists of determining which objects should be garbage collected by tracing which objects are reachable by a chain of references from certain root objects, and considering the rest as garbage and collecting them. However, there are
5750-507: 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
5865-406: 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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#17331161040555980-569: The Altair 8800 , programs with many string variables and little string space could cause long pauses due to garbage collection. Similarly the Applesoft BASIC interpreter's garbage collection algorithm repeatedly scans the string descriptors for the string having the highest address in order to compact it toward high memory, resulting in O ( n 2 ) {\displaystyle O(n^{2})} performance and pauses anywhere from
6095-785: The App Store . For iOS , garbage collection has never been introduced due to problems in application responsivity and performance; instead, iOS uses ARC. Garbage collection is rarely used on embedded or real-time systems because of the usual need for very tight control over the use of limited resources. However, garbage collectors compatible with many limited environments have been developed. The Microsoft .NET Micro Framework , .NET nanoFramework and Java Platform, Micro Edition are embedded software platforms that, like their larger cousins, include garbage collection. Garbage collectors available in Java JDKs include: Compile-time garbage collection
6210-686: 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
6325-536: 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
6440-554: 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
6555-590: 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
6670-426: The development speed when using an interpreter and the execution speed when using a compiler. Some systems (such as some Lisps ) allow interpreted and compiled code to call each other and to share variables. This means that once a routine has been tested and debugged under the interpreter it can be compiled and thus benefit from faster execution while other routines are being developed. Many interpreters do not execute
6785-524: The language specification (e.g., RPL , Java , C# , D , Go , and most scripting languages ) or effectively for practical implementation (e.g., formal languages like lambda calculus ). These are said to be garbage-collected languages . Other languages, such as C and C++ , were designed for use with manual memory management, but have garbage-collected implementations available. Some languages, like Ada , Modula-3 , and C++/CLI , allow both garbage collection and manual memory management to co-exist in
6900-516: 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
7015-473: 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
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#17331161040557130-482: 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
7245-467: The AST keeps the global program structure and relations between statements (which is lost in a bytecode representation), and when compressed provides a more compact representation. Thus, using AST has been proposed as a better intermediate format for just-in-time compilers than bytecode. Also, it allows the system to perform better analysis during runtime. However, for interpreters, an AST causes more overhead than
7360-491: 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
7475-499: The Google V8 javascript execution engine. A self-interpreter is a programming language interpreter written in a programming language which can interpret itself; an example is a BASIC interpreter written in BASIC. Self-interpreters are related to self-hosting compilers . If no compiler exists for the language to be interpreted, creating a self-interpreter requires the implementation of
7590-624: The Lisp eval function could be implemented in machine code. The result was a working Lisp interpreter which could be used to run Lisp programs, or more properly, "evaluate Lisp expressions". The development of editing interpreters was influenced by the need for interactive computing. In the 1960s, the introduction of time-sharing systems allowed multiple users to access a computer simultaneously, and editing interpreters became essential for managing and modifying code in real-time. The first editing interpreters were likely developed for mainframe computers, where they were used to create and modify programs on
7705-556: 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
7820-532: The MIPS instruction set and programming languages such as Tcl, Perl, and Java. Performance characteristics are influenced by interpreter complexity, as demonstrated by comparisons with compiled code. It is clear that interpreter performance is more dependent on the nuances and resource needs of the interpreter than it is on the particular application that is being interpreted. Lisp programming language Lisp (historically LISP , an abbreviation of "list processing")
7935-470: 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
8050-456: 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
8165-403: The allocation is done in either half of a single region of memory. When it becomes half full, a garbage collection is performed which moves the live objects into the other half and the remaining objects are implicitly deallocated. The running program (the 'mutator') has to check that any object it references is in the correct half, and if not move it across, while a background task is finding all of
8280-415: The amount of analysis performed before the program is executed. For example, Emacs Lisp is compiled to bytecode , which is a highly compressed and optimized representation of the Lisp source, but is not machine code (and therefore not tied to any particular hardware). This "compiled" code is then interpreted by a bytecode interpreter (itself written in C ). The compiled code in this case is machine code for
8395-459: The box. Interpretation cannot be used as the sole method of execution: even though an interpreter can itself be interpreted and so on, a directly executed program is needed somewhere at the bottom of the stack because the code being interpreted is not, by definition, the same as the machine code that the CPU can execute. There is a spectrum of possibilities between interpreting and compiling, depending on
8510-416: The compiled code but it can take less time to interpret it than the total time required to compile and run it. This is especially important when prototyping and testing code when an edit-interpret-debug cycle can often be much shorter than an edit-compile-run-debug cycle. Interpreting code is slower than running the compiled code because the interpreter must analyze each statement in the program each time it
8625-596: 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
8740-418: 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
8855-477: The count reaches zero, the object's memory is reclaimed. As with manual memory management, and unlike tracing garbage collection, reference counting guarantees that objects are destroyed as soon as their last reference is destroyed, and usually only accesses memory which is either in CPU caches , in objects to be freed, or directly pointed to by those, and thus tends to not have significant negative side effects on CPU cache and virtual memory operation. There are
8970-435: The efficiency of running native code, at the cost of startup time and increased memory use when the bytecode or AST is first compiled. The earliest published JIT compiler is generally attributed to work on LISP by John McCarthy in 1960. Adaptive optimization is a complementary technique in which the interpreter profiles the running program and compiles its most frequently executed parts into native code. The latter technique
9085-414: The expressiveness and elegance of a language. It also enables the interpreter to interpret its source code, the first step towards reflective interpreting. An important design dimension in the implementation of a self-interpreter is whether a feature of the interpreted language is implemented with the same feature in the interpreter's host language. An example is whether a closure in a Lisp -like language
9200-596: 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
9315-415: 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
9430-575: The fly. One of the earliest examples of an editing interpreter is the EDT (Editor and Debugger for the TECO) system, which was developed in the late 1960s for the PDP-1 computer. EDT allowed users to edit and debug programs using a combination of commands and macros, paving the way for modern text editors and interactive development environments. An interpreter usually consists of a set of known commands it can execute , and
9545-504: The functions they point to, or fetches the first instruction and jumps to it, and every instruction sequence ends with a fetch and jump to the next instruction. Unlike bytecode there is no effective limit on the number of different instructions other than available memory and address space. The classic example of threaded code is the Forth code used in Open Firmware systems: the source language
9660-474: The host language. Some languages such as Lisp and Prolog have elegant self-interpreters. Much research on self-interpreters (particularly reflective interpreters) has been conducted in the Scheme programming language , a dialect of Lisp. In general, however, any Turing-complete language allows writing of its own interpreter. Lisp is such a language, because Lisp programs are lists of symbols and other lists. XSLT
9775-504: 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,
9890-413: The interpreter and interpreted code and the typical batch environment of the time limited the advantages of interpretation. During the software development cycle , programmers make frequent changes to source code. When using a compiler, each time a change is made to the source code, they must wait for the compiler to translate the altered source files and link all of the binary code files together before
10005-449: The language in a host language (which may be another programming language or assembler ). By having a first interpreter such as this, the system is bootstrapped and new versions of the interpreter can be developed in the language itself. It was in this way that Donald Knuth developed the TANGLE interpreter for the language WEB of the de-facto standard TeX typesetting system . Defining
10120-405: The language into native calls one opcode at a time rather than creating optimized sequences of CPU executable instructions from the entire code segment. Due to the interpreter's simple design of simply passing calls directly to the hardware rather than implementing them directly, it is much faster than every other type, even bytecode interpreters, and to an extent less prone to bugs, but as a tradeoff
10235-632: The limitations of computers at the time (e.g. a shortage of program storage space, or no native support for floating point numbers). Interpreters were also used to translate between low-level machine languages, allowing code to be written for machines that were still under construction and tested on computers that already existed. The first interpreted high-level language was Lisp . Lisp was first implemented by Steve Russell on an IBM 704 computer. Russell had read John McCarthy 's paper, "Recursive Functions of Symbolic Expressions and Their Computation by Machine, Part I", and realized (to McCarthy's surprise) that
10350-572: The machine instructions from the underlying electronics so that instructions can be designed and altered more freely. It also facilitates the building of complex multi-step instructions, while reducing the complexity of computer circuits. Writing microcode is often called microprogramming and the microcode in a particular processor implementation is sometimes called a microprogram . More extensive microcoding allows small and simple microarchitectures to emulate more powerful architectures with wider word length , more execution units and so on, which
10465-421: The machine level once and for all (i.e. until the program has to be changed) while an interpreter has to do some of this conversion work every time a statement or function is executed. However, in an efficient interpreter, much of the translation work (including analysis of types, and similar) is factored out and done only the first time a program, module, function, or even statement, is run, thus quite akin to how
10580-426: The native instructions), known as a "Template". When the particular code segment is executed the interpreter simply loads or jumps to the opcode mapping in the template and directly runs it on the hardware. Due to its design, the template interpreter very strongly resembles a just-in-time compiler rather than a traditional interpreter, however it is technically not a JIT due to the fact that it merely translates code from
10695-450: The objects. Generational garbage collection schemes are based on the empirical observation that most objects die young. In generational garbage collection, two or more allocation regions (generations) are kept, which are kept separate based on the object's age. New objects are created in the "young" generation that is regularly collected, and when a generation is full, the objects that are still referenced from older regions are copied into
10810-409: The program being run. The book Structure and Interpretation of Computer Programs presents examples of meta-circular interpretation for Scheme and its dialects. Other examples of languages with a self-interpreter are Forth and Pascal . Microcode is a very commonly used technique "that imposes an interpreter between the hardware and the architectural level of a computer". As such, the microcode
10925-411: The program can be executed. The larger the program, the longer the wait. By contrast, a programmer using an interpreter does a lot less waiting, as the interpreter usually just needs to translate the code being worked on to an intermediate representation (or not translate it at all), thus requiring much less time before the changes can be tested. Effects are evident upon saving the source code and reloading
11040-458: The program. Compiled code is generally less readily debugged as editing, compiling, and linking are sequential processes that have to be conducted in the proper sequence with a proper set of commands. For this reason, many compilers also have an executive aid, known as a Makefile and program. The Makefile lists compiler and linker command lines and program source code files, but might take a simple command line menu input (e.g. "Make 3") which selects
11155-449: The programmer from manually de-allocating memory. This helps avoid some kinds of errors : GC uses computing resources to decide which memory to free. Therefore, the penalty for the convenience of not annotating object lifetime manually in the source code is overhead , which can impair program performance. A peer-reviewed paper from 2005 concluded that GC needs five times the memory to compensate for this overhead and to perform as fast as
11270-709: The programmer specifies what objects to de-allocate and return to the memory system and when to do so. Other, similar techniques include stack allocation , region inference , and memory ownership, and combinations thereof. Garbage collection may take a significant proportion of a program's total processing time, and affect performance as a result. Resources other than memory, such as network sockets , database handles , windows , file descriptors, and device descriptors, are not typically handled by garbage collection, but rather by other methods (e.g. destructors ). Some such methods de-allocate memory also. Many programming languages require garbage collection, either as part of
11385-453: The release of OS X 10.5 in 2007 Apple introduced garbage collection for Objective-C 2.0, using an in-house developed runtime collector. However, with the 2012 release of OS X 10.8 , garbage collection was deprecated in favor of LLVM 's automatic reference counter (ARC) that was introduced with OS X 10.7 . Furthermore, since May 2015 Apple even forbade the usage of garbage collection for new OS X applications in
11500-493: The same application by using separate heaps for collected and manually managed objects. Still others, like D , are garbage-collected but allow the user to manually delete objects or even disable garbage collection entirely when speed is required. Although many languages integrate GC into their compiler and runtime system , post-hoc GC systems also exist, such as Automatic Reference Counting (ARC). Some of these post-hoc GC systems do not require recompilation. GC frees
11615-474: 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
11730-619: The same object format). A simple interpreter written in a low-level language (e.g. assembly ) may have similar machine code blocks implementing functions of the high-level language stored, and executed when a function's entry in a look up table points to that code. However, an interpreter written in a high-level language typically uses another approach, such as generating and then walking a parse tree , or by generating and executing intermediate software-defined instructions, or both. Thus, both compilers and interpreters generally turn source code (text files) into tokens, both may (or may not) generate
11845-494: The same program using idealized explicit memory management. The comparison however is made to a program generated by inserting deallocation calls using an oracle , implemented by collecting traces from programs run under a profiler , and the program is only correct for one particular execution of the program. Interaction with memory hierarchy effects can make this overhead intolerable in circumstances that are hard to predict or to detect in routine testing. The impact on performance
11960-532: The source code as it stands but convert it into some more compact internal form. Many BASIC interpreters replace keywords with single byte tokens which can be used to find the instruction in a jump table . A few interpreters, such as the PBASIC interpreter, achieve even higher levels of program compaction by using a bit-oriented rather than a byte-oriented program memory structure, where commands tokens occupy perhaps 5 bits, nominally "16-bit" constants are stored in
12075-406: 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
12190-506: The third group (set) of instructions then issues the commands to the compiler, and linker feeding the specified source code files. A compiler converts source code into binary instruction for a specific processor's architecture, thus making it less portable . This conversion is made just once, on the developer's environment, and after that the same binary can be distributed to the user's machines where it can be executed without further translation. A cross compiler can generate binary code for
12305-515: The two main means by which programming languages are implemented, they are not mutually exclusive, as most interpreting systems also perform some translation work, just like compilers. The terms " interpreted language " or " compiled language " signify that the canonical implementation of that language is an interpreter or a compiler, respectively. A high-level language is ideally an abstraction independent of particular implementations. Interpreters were used as early as 1952 to ease programming within
12420-410: The user machine even if it has a different processor than the machine where the code is compiled. An interpreted program can be distributed as source code. It needs to be translated in each final machine, which takes more time but makes the program distribution independent of the machine's architecture. However, the portability of interpreted source code is dependent on the target machine actually having
12535-404: 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
12650-542: Was given by Apple as a reason for not adopting garbage collection in iOS , despite it being the most desired feature. The moment when the garbage is actually collected can be unpredictable, resulting in stalls (pauses to shift/free memory) scattered throughout a session . Unpredictable stalls can be unacceptable in real-time environments , in transaction processing , or in interactive programs. Incremental, concurrent, and real-time garbage collectors address these problems, with varying trade-offs. Tracing garbage collection
12765-420: 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
12880-502: 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
12995-520: 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 ,
13110-433: 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
13225-454: 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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