Racket is a general-purpose,

multi-paradigm programming language Programming paradigms are a way to classify programming languages based on their features. Languages can be classified into multiple paradigms. Some paradigms are concerned mainly with implications for the execution model of the language, suc ...

and a multi-platform distribution that includes the Racket language, compiler, large standard library, IDE, development tools, and a set of additional languages including Typed Racket (a sister language of Racket with a static type-checker), Swindle, FrTime, Lazy Racket, R5RS & R6RS

Scheme A scheme is a systematic plan for the implementation of a certain idea. Scheme or schemer may refer to: Arts and entertainment * ''The Scheme'' (TV series), a BBC Scotland documentary series * The Scheme (band), an English pop band * ''The Schem ...

, Scribble, Datalog, Racklog,

Algol 60 ALGOL 60 (short for ''Algorithmic Language 1960'') is a member of the ALGOL family of computer programming languages. It followed on from ALGOL 58 which had introduced code blocks and the begin and end pairs for delimiting them, representing a k ...

and several teaching languages. The Racket language is a modern dialect of

Lisp A lisp is a speech impairment in which a person misarticulates sibilants (, , , , , , , ). These misarticulations often result in unclear speech. Types * A frontal lisp occurs when the tongue is placed anterior to the target. Interdental lisping ...

and a descendant of

. It is designed as a platform for

programming language design A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language. The description of a programming la ...

and implementation. In addition to the core Racket language, ''Racket'' is also used to refer to the family of programming languages and set of tools supporting development on and with Racket. Racket is also used for

scripting Script may refer to: Writing systems * Script, a distinctive writing system, based on a repertoire of specific elements or symbols, or that repertoire * Script (styles of handwriting) ** Script typeface, a typeface with characteristics of handw ...

, computer science education, and research. The Racket platform provides an implementation of the Racket language (including a runtime system, libraries, and compiler supporting several compilation modes: machine code, machine-independent, interpreted, and JIT) along with the DrRacket integrated development environment (IDE) written in Racket. Racket is used by the

ProgramByDesign The ProgramByDesign (formerly TeachScheme!) project is an outreach effort of the PLT research group. The goal is to train college faculty, high school teachers, and possibly even middle school teachers, in programming and computing. History Matt ...

outreach program, which aims to turn computer science into "an indispensable part of the liberal arts curriculum". The core Racket language is known for its extensive

macro Macro (or MACRO) may refer to: Science and technology * Macroscopic, subjects visible to the eye * Macro photography, a type of close-up photography * Image macro, a picture with text superimposed * Monopole, Astrophysics and Cosmic Ray Observat ...

system which enables creating embedded and

domain-specific language A domain-specific language (DSL) is a computer language specialized to a particular application domain. This is in contrast to a general-purpose language (GPL), which is broadly applicable across domains. There are a wide variety of DSLs, ranging f ...

s, language constructs such as classes or modules, and separate dialects of Racket with different semantics. The platform distribution is

free and open-source software Free and open-source software (FOSS) is a term used to refer to groups of software consisting of both free software and open-source software where anyone is freely licensed to use, copy, study, and change the software in any way, and the source ...

distributed under the Apache 2.0 and MIT licenses. Extensions and packages written by the community may be uploaded to Racket's package catalog.

History

Development

Matthias Felleisen founded PLT Inc. in the mid 1990s, first as a research group, soon after as a project dedicated to producing pedagogic materials for novice programmers (lectures, exercises/projects, software). In January 1995, the group decided to develop a pedagogic programming environment based on

Matthew Flatt Matthew Flatt is an American computer scientist and professor at the University of Utah School of Computing in Salt Lake City. He is also a member of the core development team for the Racket programming language. Flatt received his PhD at Rice Univ ...

cobbled together MrEd, the original virtual machine for Racket, from libscheme, wxWidgets, and a few other free systems. In the years that followed, a team including Flatt, Robby Findler, Shriram Krishnamurthi, Cormac Flanagan, and many others produced DrScheme, a programming environment for novice Scheme programmers and a research environment for soft typing. The main development language that DrScheme supported was named PLT Scheme. In parallel, the team began conducting workshops for high school teachers, training them in program design and functional programming. Field tests with these teachers and their students provided essential clues for directing the development. Over the following years, PLT added teaching languages, an algebraic stepper, a transparent read–eval–print loop, a constructor-based printer, and many other innovations to DrScheme, producing an application-quality pedagogic program development environment. By 2001, the core team (Felleisen, Findler, Flatt, Krishnamurthi) had also written and published their first textbook, '' How to Design Programs'', based on their teaching philosophy. ''The Racket Manifesto'' details the principles driving the development of Racket, presents the evaluation framework behind the design process, and details opportunities for future improvements.

Version history

The first generation of PLT Scheme revisions introduced features for programming in the large with both modules and classes. Version 42 introduced units – a first-class module system – to complement classes for large scale development. The class system gained features (e.g. Java-style

interfaces Interface or interfacing may refer to: Academic journals * Interface (journal), ''Interface'' (journal), by the Electrochemical Society * ''Interface, Journal of Applied Linguistics'', now merged with ''ITL International Journal of Applied Lin ...

) and also lost several features (e.g. multiple inheritance) throughout these versions. The language evolved throughout a number of successive versions, and gaining milestone popularity in Version 53, leading to extensive work and the following Version 100, which would be equivalent to a "1.0" release in current popular version systems. The next major revision was named Version 200, which introduced a new default module system that cooperates with macros. In particular, the module system ensures that run-time and compile-time computation are separated to support a "tower of languages". Unlike units, these modules are not first-class objects. Version 300 introduced Unicode support, foreign library support, and refinements to the class system. Later on, the 300 series improved the

performance A performance is an act of staging or presenting a play, concert, or other form of entertainment. It is also defined as the action or process of carrying out or accomplishing an action, task, or function. Management science In the work place ...

of the language runtime with an addition of a JIT compiler and a switch to a default

generational garbage collection In computer programming, tracing garbage collection is a form of automatic memory management that consists of determining which objects should be deallocated ("garbage collected") by tracing which objects are ''reachable'' by a chain of references ...

. By the next major release, the project had switched to a more conventional sequence-based version numbering. Version 4.0 introduced the #lang shorthand to specify the language that a module is written in. Further, the revision introduced

immutable In object-oriented and functional programming, an immutable object (unchangeable object) is an object whose state cannot be modified after it is created.Goetz et al. ''Java Concurrency in Practice''. Addison Wesley Professional, 2006, Section 3.4 ...

pairs and lists, support for fine-grained parallelism, and a statically-typed dialect. On 7 June 2010, PLT Scheme was renamed Racket. The renaming coincided with the release of Version 5.0. Subsequently, the graphical user interface (GUI) backend was rewritten in Racket from C++ in Version 5.1 using native UI toolkits on all platforms. Version 5.2 included a background syntax checking tool, a new plotting library, a database library, and a new extended REPL. Version 5.3 included a new submodule feature for optionally loaded modules, new optimization tools, a

JSON JSON (JavaScript Object Notation, pronounced ; also ) is an open standard file format and data interchange format that uses human-readable text to store and transmit data objects consisting of attribute–value pairs and arrays (or other ser ...

library, and other features. Version 5.3.1 introduced major improvements to DrRacket: the background syntax checker was turned on by default and a new documentation preview tool was added. In version 6.0, Racket released its second-generation package management system. As part of this development, the principal DrRacket and Racket repository was reorganized and split into a large set of small packages, making it possible to install a ''minimal racket'' and to install only those packages needed. Version 7 of Racket was released with a new macro expander written in Racket as part the preparations for supporting moving to the Chez Scheme runtime system and supporting multiple runtime systems. On 19 November 2019, Racket 7.5 was released. The license of Racket 7.5 was less restrictive. They use now either the Apache 2.0 license or the MIT license. On 2021 February 13, Racket 8.0 was released. Racket 8.0 marks the first release where Racket with the Chez Scheme runtime system, known as Racket CS, is the default implementation. Racket CS is faster, easier to maintain and develop, backward-compatible with existing Racket programs, and has better parallel garbage collection.

Features

Racket's core language includes macros, modules, lexical closures, tail calls,

delimited continuation In programming languages, a delimited continuation, composable continuation or partial continuation, is a "slice" of a continuation frame that has been reified into a function. Unlike regular continuations, delimited continuations return a value, a ...

s, parameters (fluid variables), software contracts, green threads and OS threads, and more. The language also comes with primitives, such as eventspaces and custodians, which control resource management and enables the language to act like an operating system for loading and managing other programs. Further extensions to the language are created with the powerful macro system, which together with the module system and custom parsers can control all aspects of a language. Most language constructs in Racket are implemented as macros in the base language. These include a mixin class system, a component (or module) system as expressive as opaque ascription in the ML module system, and pattern matching. Further, the language features the first contract system for a higher-order programming language. Racket's contract system is inspired by the Design by Contract work for

Eiffel Eiffel may refer to: Places * Eiffel Peak, a summit in Alberta, Canada * Champ de Mars – Tour Eiffel station, Paris, France; a transit station Structures * Eiffel Tower, in Paris, France, designed by Gustave Eiffel * Eiffel Bridge, Ungheni, M ...

and extends it to work for higher-order values such as first-class functions, objects, reference cells, and so on. For example, an object that is checked by a contract can be ensured to make contract checks when its methods are eventually invoked. Racket includes both

bytecode Bytecode (also called portable code or p-code) is a form of instruction set designed for efficient execution by a software interpreter. Unlike human-readable source code, bytecodes are compact numeric codes, constants, and references (norma ...

and JIT (JIT) compilers. The bytecode compiler produces an internal bytecode format run by the Racket virtual machine, and the JIT compiler translates bytecode to machine code at runtime. Since 2004, the language has also shipped with PLaneT, a package manager that is integrated into the module system so that third-party libraries can be transparently imported and used. Also, PLaneT has a built-in versioning policy to prevent dependency hell. At the end of 2014, much of Racket's code was moved into a new packaging system separate from the main code base. This new packaging system is serviced by a client program named ''raco''. The new package system provides fewer features than PLaneT; a blog post by Jay McCarthy on the Racket blog explains the rationale for the change and how to duplicate the older system.

Integrated language extensibility and macros

The features that most clearly distinguish Racket from other languages in the Lisp family are its integrated language

extensibility Extensibility is a software engineering and systems design principle that provides for future growth. Extensibility is a measure of the ability to extend a system and the level of effort required to implement the extension. Extensions can be th ...

features that support building new domain-specific and general-purpose languages. Racket's extensibility features are built into the module system to allow context-sensitive and module-level control over syntax. For example, the #%app syntactic form can be overridden to change the semantics of

function application In mathematics, function application is the act of applying a function to an argument from its domain so as to obtain the corresponding value from its range. In this sense, function application can be thought of as the opposite of function abst ...

. Similarly, the #%module-begin form allows arbitrary static analysis of the entire module. Since any module can be used as a language, via the #lang notation, this effectively means that virtually any aspect of the language can be programmed and controlled. The module-level extensibility features are combined with a

-like hygienic macro system, which provides more features than Lisp's s-expression manipulation system, Scheme 84's hygienic extend-syntax macros, or R5RS's

syntax-rules Hygienic macros are macros whose expansion is guaranteed not to cause the accidental capture of identifiers. They are a feature of programming languages such as Scheme, Dylan, Rust, Nim, and Julia. The general problem of accidental capture was ...

. Indeed, it is fair to say that the macro system is a carefully tuned

application programming interface An application programming interface (API) is a way for two or more computer programs to communicate with each other. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how t ...

(API) for compiler extensions. Using this compiler API, programmers can add features and entire

s in a manner that makes them completely indistinguishable from built-in language constructs. The ''macro'' system in Racket has been used to construct entire language dialects. This includes Typed Racket, which is a gradually typed dialect of Racket that eases the migration from untyped to typed code, Lazy Racket—a dialect with lazy evaluation, and Hackett, which combines Haskell and Racket. The pedagogical programming language Pyret was originally implemented in Racket. Other dialects include FrTime ( functional reactive programming), Scribble (documentation language), Slideshow ( presentation language), and several languages for education. Racket's core distribution provides libraries to aid the development of programming languages. Such languages are not restricted to s-expression based syntax. In addition to conventional readtable-based syntax extensions, the directive #lang enables the invocation of arbitrary parsers, which can be implemented using the parser tools library. See Racket logic programming for an example of such a language.

Programming environment

The language platform provides a self-hosted IDE named DrRacket, a continuation-based

web server A web server is computer software and underlying hardware that accepts requests via HTTP (the network protocol created to distribute web content) or its secure variant HTTPS. A user agent, commonly a web browser or web crawler, initiate ...

, a graphical user interface, and other tools. As a viable scripting tool with libraries like common scripting languages, it can be used for scripting the Unix shell. It can parse command line arguments and execute external tools.

DrRacket IDE

DrRacket (formerly DrScheme) is widely used among introductory computer science courses that teach Scheme or Racket and is lauded for its simplicity and appeal to beginner programmers. The IDE was originally built for use with the TeachScheme! project (now

), an outreach effort by

Northeastern University Northeastern University (NU) is a private university, private research university with its main campus in Boston. Established in 1898, the university offers undergraduate and graduate programs on its main campus as well as satellite campuses in ...

and a number of affiliated universities for attracting high school students to computer science courses at the college level. The editor provides highlighting for syntax and run-time errors, parenthesis matching, a debugger and an algebraic stepper. Its student-friendly features include support for multiple "language levels" (Beginning Student, Intermediate Student and so on). It also has integrated library support, and sophisticated analysis tools for advanced programmers. Further, module-oriented programming is supported with the module browser, a contour view, integrated

testing An examination (exam or evaluation) or test is an educational assessment intended to measure a test-taker's knowledge, skill, aptitude, physical fitness, or classification in many other topics (e.g., beliefs). A test may be administered verba ...

and coverage measurements, and refactoring support. It provides integrated, context-sensitive access to an extensive hyper-linked help system named "Help Desk". DrRacket is available for Windows, macOS, Unix, and Linux with the X Window System and programs behave similarly on all these platforms.

Code examples

Here is a trivial hello world program: #lang racket "Hello, World!" Running this program produces the output: : Here is a slightly less trivial program: Sierpinski Racket example

#lang racket (require 2htdp/image) (let sierpinski ( 8 (if (zero? n) (triangle 2 'solid 'red) (let ( (sierpinski (- n 1)) (freeze (above t (beside t t)))))) This program, taken from the Racket website, draws a Sierpinski triangle, nested to depth 8. Using the #lang directive, a source file can be written in different dialects of Racket. Here is an example of the factorial program in Typed Racket, a

statically typed In computer programming, a type system is a logical system comprising a set of rules that assigns a property called a type to every "term" (a word, phrase, or other set of symbols). Usually the terms are various constructs of a computer progra ...

dialect of Racket: #lang typed/racket (: fact (Integer -> Integer)) (define (fact n) (if (zero? n) 1 (* n (fact (- n 1)))))

Applications and practical use

Apart from having a basis in

programming language theory Programming language theory (PLT) is a branch of computer science that deals with the design, implementation, analysis, characterization, and classification of formal languages known as programming languages. Programming language theory is clos ...

, Racket was designed as a general-purpose language for production systems. Thus, the Racket distribution features an extensive library that covers systems and network programming, web development, a uniform interface to the underlying operating system, a dynamic foreign function interface, several flavours of regular expressions, lexer/parser generators, logic programming, and a complete GUI framework. Racket has several features useful for a commercial language, among them an ability to compile standalone executables under Windows, macOS, and Unix, a profiler and debugger included in the integrated development environment (IDE), and a unit testing framework. Racket has been used for commercial projects and web applications. A notable example is the Hacker News website, which runs on

Arc ARC may refer to: Business * Aircraft Radio Corporation, a major avionics manufacturer from the 1920s to the '50s * Airlines Reporting Corporation, an airline-owned company that provides ticket distribution, reporting, and settlement services * ...

, which is developed in Racket. Naughty Dog has used it as a scripting language in several of their video games. Racket is used to teach students algebra through game design in the

Bootstrap program In computing, booting is the process of starting a computer as initiated via hardware such as a button or by a software command. After it is switched on, a computer's central processing unit (CPU) has no software in its main memory, so some ...

References

External links