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In computer science, a continuation is an abstract representation of the
control state Alcoholic beverage control states, generally called control states, less often ABC states, are 17 states in the United States that, as of 2016, have state monopoly over the wholesaling or retailing of some or all categories of alcoholic beverag ...
of a computer program. A continuation implements ( reifies) the program control state, i.e. the continuation is a data structure that represents the computational process at a given point in the process's execution; the created data structure can be accessed by the programming language, instead of being hidden in the runtime environment. Continuations are useful for encoding other control mechanisms in programming languages such as exceptions, generators, coroutines, and so on. The "current continuation" or "continuation of the computation step" is the continuation that, from the perspective of running code, would be derived from the current point in a program's execution. The term ''continuations'' can also be used to refer to first-class continuations, which are constructs that give a programming language the ability to save the execution state at any point and return to that point at a later point in the program, possibly multiple times.


History

The earliest description of continuations was made by
Adriaan van Wijngaarden Adriaan "Aad" van Wijngaarden (2 November 1916 – 7 February 1987) was a Dutch mathematician and computer scientist. Trained as an engineer, Van Wijngaarden would emphasize and promote the mathematical aspects of computing, first in numerical an ...
in September 1964. Wijngaarden spoke at the IFIP Working Conference on Formal Language Description Languages held in Baden bei Wien, Austria. As part of a formulation for an
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 ...
preprocessor, he called for a transformation of proper procedures into continuation-passing style, though he did not use this name, and his intention was to simplify a program and thus make its result more clear.
Christopher Strachey Christopher S. Strachey (; 16 November 1916 – 18 May 1975) was a British computer scientist. He was one of the founders of denotational semantics, and a pioneer in programming language design and computer time-sharing.F. J. Corbató, et al., ...
,
Christopher P. Wadsworth Christopher is the English version of a Europe-wide name derived from the Greek name Χριστόφορος (''Christophoros'' or '' Christoforos''). The constituent parts are Χριστός (''Christós''), "Christ" or "Anointed", and φέρει ...
and
John C. Reynolds John Charles Reynolds (June 1, 1935 – April 28, 2013) was an American computer scientist. Education and affiliations John Reynolds studied at Purdue University and then earned a Doctor of Philosophy (Ph.D.) in theoretical physics from Harvard U ...
brought the term ''continuation'' into prominence in their work in the field of
denotational semantics In computer science, denotational semantics (initially known as mathematical semantics or Scott–Strachey semantics) is an approach of formalizing the meanings of programming languages by constructing mathematical objects (called ''denotations'' ...
that makes extensive use of continuations to allow sequential programs to be analysed in terms of functional programming semantics. Steve Russell invented the continuation in his second
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 ...
implementation for the
IBM 704 The IBM 704 is a large digital mainframe computer introduced by IBM in 1954. It was the first mass-produced computer with hardware for floating-point arithmetic. The IBM 704 ''Manual of operation'' states: The type 704 Electronic Data-Pro ...
, though he did not name it. gives a complete history of the discovery of continuations.


First-class continuations

First-class continuations are a language's ability to completely control the execution order of instructions. They can be used to jump to a function that produced the call to the current function, or to a function that has previously exited. One can think of a first-class continuation as saving the ''execution'' state of the program. It is important to note that true first-class continuations do not save program data – unlike a process image – only the execution context. This is illustrated by the "continuation sandwich" description:
''Say you're in the kitchen in front of the refrigerator, thinking about a sandwich. You take a continuation right there and stick it in your pocket. Then you get some turkey and bread out of the refrigerator and make yourself a sandwich, which is now sitting on the counter. You invoke the continuation in your pocket, and you find yourself standing in front of the refrigerator again, thinking about a sandwich. But fortunately, there's a sandwich on the counter, and all the materials used to make it are gone. So you eat it. :-)''
In this description, the sandwich is part of the program ''data'' (e.g., an object on the heap), and rather than calling a "make sandwich" routine and then returning, the person called a "make sandwich with current continuation" routine, which creates the sandwich and then continues where execution left off.
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 ...
was the first full production system (1969-1970), providing first "catch" and then call/cc. Bruce Duba introduced call/cc into SML. Continuations are also used in models of computation including
denotational semantics In computer science, denotational semantics (initially known as mathematical semantics or Scott–Strachey semantics) is an approach of formalizing the meanings of programming languages by constructing mathematical objects (called ''denotations'' ...
, the
actor model The actor model in computer science is a mathematical model of concurrent computation that treats ''actor'' as the universal primitive of concurrent computation. In response to a message it receives, an actor can: make local decisions, create more ...
, process calculi, and
lambda calculus Lambda calculus (also written as ''λ''-calculus) is a formal system in mathematical logic for expressing computation based on function abstraction and application using variable binding and substitution. It is a universal model of computation ...
. These models rely on programmers or semantics engineers to write mathematical functions in the so-called continuation-passing style. This means that each function consumes a function that represents the rest of the computation relative to this function call. To return a value, the function calls this "continuation function" with a return value; to abort the computation it returns a value. Functional programmers who write their programs in continuation-passing style gain the expressive power to manipulate the flow of control in arbitrary ways. The cost is that they must maintain the invariants of control and continuations by hand, which can be a highly complex undertaking (but see 'continuation-passing style' below).


Uses

Continuations simplify and clarify the implementation of several common design patterns, including coroutines/ green threads and exception handling, by providing the basic, low-level primitive which unifies these seemingly unconnected patterns. Continuations can provide elegant solutions to some difficult high-level problems, like programming a web server that supports multiple pages, accessed by the use of the forward and back buttons and by following links. The
Smalltalk Smalltalk is an object-oriented, dynamically typed reflective programming language. It was designed and created in part for educational use, specifically for constructionist learning, at the Learning Research Group (LRG) of Xerox PARC by Alan Ka ...
Seaside web framework uses continuations to great effect, allowing one to program the web server in procedural style, by switching continuations when switching pages. More complex constructs for which ''"continuations provide an elegant description"'' also exist. For example, in C,
longjmp setjmp.h is a header defined in the C standard library to provide "non-local jumps": control flow that deviates from the usual subroutine call and return sequence. The complementary functions setjmp and longjmp provide this functionality. A t ...
can be used to jump from the middle of one function to another, provided the second function lies deeper in the stack (if it is waiting for the first function to return, possibly among others). Other more complex examples include coroutines in
Simula 67 Simula is the name of two simulation programming languages, Simula I and Simula 67, developed in the 1960s at the Norwegian Computing Center in Oslo, by Ole-Johan Dahl and Kristen Nygaard. Syntactically, it is an approximate superset of ALGOL ...
,
Lua Lua or LUA may refer to: Science and technology * Lua (programming language) * Latvia University of Agriculture * Last universal ancestor, in evolution Ethnicity and language * Lua people, of Laos * Lawa people, of Thailand sometimes referred t ...
, and Perl; tasklets in Stackless Python; generators in Icon and Python; continuations in Scala (starting in 2.8);
fibers Fiber or fibre (from la, fibra, links=no) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often incorporate ...
in Ruby (starting in 1.9.1); the backtracking mechanism in Prolog; monads in functional programming; and
threads Thread may refer to: Objects * Thread (yarn), a kind of thin yarn used for sewing ** Thread (unit of measurement), a cotton yarn measure * Screw thread, a helical ridge on a cylindrical fastener Arts and entertainment * ''Thread'' (film), 2016 ...
.


Examples

The
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 ...
programming language includes the control operator
call-with-current-continuation In the Scheme computer programming language, the procedure call-with-current-continuation, abbreviated call/cc, is used as a control flow operator. It has been adopted by several other programming languages. Taking a function f as its only argum ...
(abbreviated as: call/cc) with which a Scheme program can manipulate the flow of control: (define the-continuation #f) (define (test) (let ((i 0)) ; call/cc calls its first function argument, passing ; a continuation variable representing this point in ; the program as the argument to that function. ; ; In this case, the function argument assigns that ; continuation to the variable the-continuation. ; (call/cc (lambda (k) (set! the-continuation k))) ; ; The next time the-continuation is called, we start here. (set! i (+ i 1)) i)) Using the above, the following code block defines a function test that sets the-continuation to the future execution state of itself: > (test) 1 > (the-continuation) 2 > (the-continuation) 3 > ; stores the current continuation (which will print 4 next) away > (define another-continuation the-continuation) > (test) ; resets the-continuation 1 > (the-continuation) 2 > (another-continuation) ; uses the previously stored continuation 4 For a gentler introduction to this mechanism, see
call-with-current-continuation In the Scheme computer programming language, the procedure call-with-current-continuation, abbreviated call/cc, is used as a control flow operator. It has been adopted by several other programming languages. Taking a function f as its only argum ...
.


Coroutines

This example shows a possible usage of continuations to implement
coroutines Coroutines are computer program components that generalize subroutines for non-preemptive multitasking, by allowing execution to be suspended and resumed. Coroutines are well-suited for implementing familiar program components such as cooperative ...
as separate threads. ;;; A naive queue for thread scheduling. ;;; It holds a list of continuations "waiting to run". (define *queue* '()) (define (empty-queue?) (null? *queue*)) (define (enqueue x) (set! *queue* (append *queue* (list x)))) (define (dequeue) (let ((x (car *queue*))) (set! *queue* (cdr *queue*)) x)) ;;; This starts a new thread running (proc). (define (fork proc) (call/cc (lambda (k) (enqueue k) (proc)))) ;;; This yields the processor to another thread, if there is one. (define (yield) (call/cc (lambda (k) (enqueue k) ((dequeue))))) ;;; This terminates the current thread, or the entire program ;;; if there are no other threads left. (define (thread-exit) (if (empty-queue?) (exit) ((dequeue)))) The functions defined above allow for defining and executing threads through cooperative multitasking, i.e. threads that yield control to the next one in a queue: ;;; The body of some typical Scheme thread that does stuff: (define (do-stuff-n-print str) (lambda () (let loop ((n 0)) (format #t "~A ~A\n" str n) (yield) (loop (+ n 1))))) ;;; Create two threads, and start them running. (fork (do-stuff-n-print "This is AAA")) (fork (do-stuff-n-print "Hello from BBB")) (thread-exit) The previous code will produce this output: This is AAA 0 Hello from BBB 0 This is AAA 1 Hello from BBB 1 This is AAA 2 Hello from BBB 2 ...


Implementation

A program must allocate space in memory for the variables its functions use. Most programming languages use a call stack for storing the variables needed because it allows for fast and simple allocating and automatic deallocation of memory. Other programming languages use a
heap Heap or HEAP may refer to: Computing and mathematics * Heap (data structure), a data structure commonly used to implement a priority queue * Heap (mathematics), a generalization of a group * Heap (programming) (or free store), an area of memory f ...
for this, which allows for flexibility at a higher cost for allocating and deallocating memory. Both of these implementations have benefits and drawbacks in the context of continuations.


Programming language support

Many programming languages exhibit first-class continuations under various names; specifically: *
Common Lisp Common Lisp (CL) is a dialect of the Lisp programming language, published in ANSI standard document ''ANSI INCITS 226-1994 (S20018)'' (formerly ''X3.226-1994 (R1999)''). The Common Lisp HyperSpec, a hyperlinked HTML version, has been derived fro ...

cl-cont
One can also use custom macros * C# /
VB.NET Visual Basic, originally called Visual Basic .NET (VB.NET), is a multi-paradigm, object-oriented programming language, implemented on .NET, Mono, and the .NET Framework. Microsoft launched VB.NET in 2002 as the successor to its original Visua ...
: async and await: "sign up the rest of method as the continuation, and then return to your caller immediately; the task will invoke the continuation when it completes.
Asynchronous Programming for C#
* Factor: callcc0 and callcc1 * Haskell: The Continuation monad in Control.Monad.Cont
/code> * Haxe
haxe-continuation
* Icon, Unicon : create, suspend, @ operator: coexpressions * Java
Lightwolfjavaflow
(requires bytecode manipulation at runtime or compile time) * Kotlin : Continuation * JavaScript Rhino : Continuation * Parrot: Continuation PMC; uses continuation-passing style for all control flow * Perl
Coro
an
Continuity
*
Pico Pico may refer to: Places The Moon * Mons Pico, a lunar mountain in the northern part of the Mare Imbrium basin Portugal * Pico, a civil parish in the municipality of Vila Verde * Pico da Pedra, a civil parish in the municipality of Ribei ...
: call(exp()) and continue(aContinuation, anyValue) * Python: PyPy's _continuation.continulet
/code> *
Racket Racket may refer to: * Racket (crime), a systematised element of organized crime ** Protection racket, a scheme whereby a group provides protection to businesses or other groups through violence outside the sanction of the law * Racket (sports equ ...
:
call-with-current-continuation In the Scheme computer programming language, the procedure call-with-current-continuation, abbreviated call/cc, is used as a control flow operator. It has been adopted by several other programming languages. Taking a function f as its only argum ...
(commonly shortened to call/cc) * Ruby: callcc * Scala: scala.util.continuations provides shift/reset *
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 ...
:
call-with-current-continuation In the Scheme computer programming language, the procedure call-with-current-continuation, abbreviated call/cc, is used as a control flow operator. It has been adopted by several other programming languages. Taking a function f as its only argum ...
(commonly shortened to call/cc) *
Smalltalk Smalltalk is an object-oriented, dynamically typed reflective programming language. It was designed and created in part for educational use, specifically for constructionist learning, at the Learning Research Group (LRG) of Xerox PARC by Alan Ka ...
: Continuation currentDo:; in most modern Smalltalk environments continuations can be implemented without additional VM support. *
Standard ML of New Jersey Standard ML of New Jersey (SML/NJ; Standard Meta-Language of New Jersey) is a free and open-source compiler and programming environment for the Standard ML programming language. Aside from its runtime system, which is written in C, SML/NJ is wr ...
: SMLofNJ.Cont.callcc * Unlambda: c, the flow control operation for call with current continuation In any language which supports closures and proper tail calls, it is possible to write programs in continuation-passing style and manually implement call/cc. (In continuation-passing style, call/cc becomes a simple function that can be written with lambda.) This is a particularly common strategy in Haskell, where it is easy to construct a "continuation-passing monad" (for example, the Cont monad and ContT monad transformer in the mtl library). The support for proper tail calls is needed because in continuation-passing style no function ever returns; ''all'' calls are tail calls.


In Web development

One area that has seen practical use of continuations is in Web programming. The use of continuations shields the programmer from the stateless nature of the HTTP protocol. In the traditional model of web programming, the lack of state is reflected in the program's structure, leading to code constructed around a model that lends itself very poorly to expressing computational problems. Thus continuations enable code that has the useful properties associated with inversion of control, while avoiding its problems. Inverting back the inversion of control or, Continuations versus page-centric programming
/cite> is a paper that provides a good introduction to continuations applied to web programming.


Kinds

Support for continuations varies widely. A programming language supports ''re-invocable'' continuations if a continuation may be invoked repeatedly (even after it has already returned). Re-invocable continuations were introduced by
Peter J. Landin Peter John Landin (5 June 1930 – 3 June 2009) was a British computer scientist. He was one of the first to realise that the lambda calculus could be used to model a programming language, an insight that is essential to the development of bo ...
using his J (for Jump) operator that could transfer the flow of control back into the middle of a procedure invocation. Re-invocable continuations have also been called "re-entrant" in the
Racket Racket may refer to: * Racket (crime), a systematised element of organized crime ** Protection racket, a scheme whereby a group provides protection to businesses or other groups through violence outside the sanction of the law * Racket (sports equ ...
language. However this use of the term "re-entrant" can be easily confused with its use in discussions of multithreading. A more limited kind is the ''escape continuation'' that may be used to escape the current context to a surrounding one. Many languages which do not explicitly support continuations support exception handling, which is equivalent to escape continuations and can be used for the same purposes. C's
setjmp/longjmp setjmp.h is a header defined in the C standard library to provide "non-local jumps": control flow that deviates from the usual subroutine call and return sequence. The complementary functions setjmp and longjmp provide this functionality. A ...
are also equivalent: they can only be used to unwind the stack. Escape continuations can also be used to implement
tail call elimination In computer science, a tail call is a subroutine call performed as the final action of a procedure. If the target of a tail is the same subroutine, the subroutine is said to be tail recursive, which is a special case of direct recursion (computer s ...
. One generalization of continuations are
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. Continuation operators like call/cc capture the ''entire'' remaining computation at a given point in the program and provide no way of delimiting this capture. Delimited continuation operators address this by providing two separate control mechanisms: a ''prompt'' that delimits a continuation operation and a ''reification'' operator such as shift or control. Continuations captured using delimited operators thus only represent a slice of the program context.


Disadvantages

Continuations are the functional expression of the
GOTO GoTo (goto, GOTO, GO TO or other case combinations, depending on the programming language) is a statement found in many computer programming languages. It performs a one-way transfer of control to another line of code; in contrast a function ca ...
statement, and the same caveats apply. While they are a sensible option in some special cases such as web programming, use of continuations can result in code that is difficult to follow. In fact, the esoteric programming language Unlambda includes
call-with-current-continuation In the Scheme computer programming language, the procedure call-with-current-continuation, abbreviated call/cc, is used as a control flow operator. It has been adopted by several other programming languages. Taking a function f as its only argum ...
as one of its features solely because expressions involving it "tend to be hopelessly difficult to track down." The external links below illustrate the concept in more detail.


Linguistics

In "Continuations and the nature of quantification", Chris Barker introduced the "continuation hypothesis", that
some linguistic expressions (in particular, QNPs uantificational noun phrases have denotations that manipulate their own continuations.
Barker argued that this hypothesis could be used to explain phenomena such as ''duality of NP meaning'' (e.g., the fact that the QNP "everyone" behaves very differently from the non-quantificational noun phrase "Bob" in contributing towards the meaning of a sentence like "Alice sees ob/everyone), ''scope displacement'' (e.g., that "a raindrop fell on every car" is interpreted typically as \forall c \exists r, \mbox(r,c) rather than as \exists r \forall c, \mbox(r,c)), and ''scope ambiguity'' (that a sentence like "someone saw everyone" may be ambiguous between \exists x \forall y, \mbox(x,y) and \forall y \exists x, \mbox(x,y)). He also observed that this idea is in a way just a natural extension of Richard Montague's approach in "The Proper Treatment of Quantification in Ordinary English" (PTQ), writing that "with the benefit of hindsight, a limited form of continuation-passing is clearly discernible at the core of Montague’s (1973) PTQ treatment of NPs as generalized quantifiers". The extent to which continuations can be used to explain other general phenomena in natural language is a topic of current research.See for example Chris Barker,
Continuations in Natural Language
(Continuations Workshop 2004), or Chung-chieh Shan,
Linguistic Side Effects
(in "Direct compositionality,'' ed. Chris Barker and Pauline Jacobson, pp. 132-163, Oxford University Press, 2007).


See also

*
Call-with-current-continuation In the Scheme computer programming language, the procedure call-with-current-continuation, abbreviated call/cc, is used as a control flow operator. It has been adopted by several other programming languages. Taking a function f as its only argum ...
* Closure * COMEFROM * Continuation-passing style * Control flow * Coroutine *
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 ...
*
Denotational semantics In computer science, denotational semantics (initially known as mathematical semantics or Scott–Strachey semantics) is an approach of formalizing the meanings of programming languages by constructing mathematical objects (called ''denotations'' ...
*
GOTO GoTo (goto, GOTO, GO TO or other case combinations, depending on the programming language) is a statement found in many computer programming languages. It performs a one-way transfer of control to another line of code; in contrast a function ca ...
*
Spaghetti stack In computer science, an in-tree or parent pointer tree is an -ary tree data structure in which each node has a pointer to its parent node, but no pointers to child nodes. When used to implement a set of stacks, the structure is called a spaghett ...
* Quajects, a type of object which allows selectable continuations (called 'callouts') to be set for methods on a per-object basis, through Dependency Injection.


References


Further reading

* Peter Landin. ''A Generalization of Jumps and Labels'' Report. UNIVAC Systems Programming Research. August 1965. Reprinted in Higher Order and Symbolic Computation, 11(2):125-143, 1998, with a foreword by Hayo Thielecke. *
Drew McDermott Drew McDermott (December 27, 1949 – May 26, 2022) was a professor of Computer Science at Yale University. He was known for his contributions in artificial intelligence and planning. Education Drew McDermott earned Bachelor of Science, B.S., Mas ...
and
Gerry Sussman Gerald Jay Sussman (born February 8, 1947) is the Panasonic Professor of Electrical engineering, Electrical Engineering at the Massachusetts Institute of Technology (MIT). He received his Bachelor of Science, S.B. and Doctor of Philosophy, Ph.D. ...
. ''The Conniver Reference Manual'' MIT AI Memo 259. May 1972. *
Daniel Bobrow Daniel Gureasko Bobrow (29 November 1935 – 20 March 2017) was an American computer scientist who created an oft-cited artificial intelligence program STUDENT, with which he earned his PhD., worked at BBN Technologies (BBN), then was a Research Fe ...
: ''A Model for Control Structures for Artificial Intelligence Programming Languages'' IJCAI 1973. * Carl Hewitt,
Peter Bishop Peter Bishop is a fictional character of the Fox television series ''Fringe''. He is portrayed by Joshua Jackson Joshua Carter Jackson (born June 11, 1978) is a Canadian-American actor. He is known for his starring role as Charlie Conway in ...
and
Richard Steiger Richard is a male given name. It originates, via Old French, from Old Frankish and is a compound of the words descending from Proto-Germanic ''*rīk-'' 'ruler, leader, king' and ''*hardu-'' 'strong, brave, hardy', and it therefore means 'str ...
. ''A Universal Modular Actor Formalism for Artificial Intelligence'' IJCAI 1973. *
Christopher Strachey Christopher S. Strachey (; 16 November 1916 – 18 May 1975) was a British computer scientist. He was one of the founders of denotational semantics, and a pioneer in programming language design and computer time-sharing.F. J. Corbató, et al., ...
and
Christopher P. Wadsworth Christopher is the English version of a Europe-wide name derived from the Greek name Χριστόφορος (''Christophoros'' or '' Christoforos''). The constituent parts are Χριστός (''Christós''), "Christ" or "Anointed", and φέρει ...
. ''Continuations: a Mathematical semantics for handling full jumps'' Technical Monograph PRG-11. Oxford University Computing Laboratory. January 1974. Reprinted in Higher Order and Symbolic Computation, 13(1/2):135—152, 2000, with a foreword by Christopher P. Wadsworth. *
John C. Reynolds John Charles Reynolds (June 1, 1935 – April 28, 2013) was an American computer scientist. Education and affiliations John Reynolds studied at Purdue University and then earned a Doctor of Philosophy (Ph.D.) in theoretical physics from Harvard U ...
. ''Definitional Interpreters for Higher-Order Programming Languages'' Proceedings of 25th ACM National Conference, pp. 717–740, 1972. Reprinted in Higher-Order and Symbolic Computation 11(4):363-397, 1998, with a foreword. *John C. Reynolds. ''On the Relation between Direct and Continuation Semantics'' Proceedings of Second Colloquium on Automata, Languages, and Programming. LNCS Vol. 14, pp. 141–156, 1974. * * Gerald Sussman and Guy Steele. ''SCHEME: An Interpreter for Extended Lambda Calculus'' AI Memo 349, MIT Artificial Intelligence Laboratory, Cambridge, Massachusetts, December 1975. Reprinted in Higher-Order and Symbolic Computation 11(4):405-439, 1998, with a foreword. *
Robert Hieb The name Robert is an ancient Germanic given name, from Proto-Germanic "fame" and "bright" (''Hrōþiberhtaz''). Compare Old Dutch ''Robrecht'' and Old High German ''Hrodebert'' (a compound of '' Hruod'' ( non, Hróðr) "fame, glory, honou ...
, R. Kent Dybvig,
Carl Bruggeman Carl may refer to: * Carl, Georgia, city in USA * Carl, West Virginia, an unincorporated community *Carl (name), includes info about the name, variations of the name, and a list of people with the name * Carl², a TV series * "Carl", an episode of ...
. ''Representing Control in the Presence of First-Class Continuations'' Proceedings of the ACM SIGPLAN '90 Conference on Programming Language Design and Implementation, pp. 66–77. *
Will Clinger William D. Clinger is an associate professor in the Khoury College of Computer Sciences at Northeastern University. He is known for his work on higher-order and functional programming languages, and for extensive contributions in helping create an ...
,
Anne Hartheimer Anne, alternatively spelled Ann, is a form of the Latin female given name Anna. This in turn is a representation of the Hebrew Hannah, which means 'favour' or 'grace'. Related names include Annie. Anne is sometimes used as a male name in the ...
,
Eric Ost The given name Eric, Erich, Erikk, Erik, Erick, or Eirik is derived from the Old Norse name ''Eiríkr'' (or ''Eríkr'' in Old East Norse due to monophthongization). The first element, ''ei-'' may be derived from the older Proto-Norse ''* ...
. ''Implementation Strategies for Continuations'' Proceedings of the 1988 ACM conference on LISP and Functional Programming, pp. 124–131, 1988. Journal version: Higher-Order and Symbolic Computation, 12(1):7-45, 1999. *
Christian Queinnec Christians () are people who follow or adhere to Christianity, a monotheistic Abrahamic religion based on the life and teachings of Jesus Christ. The words ''Christ'' and ''Christian'' derive from the Koine Greek title ''Christós'' (Χρισ ...
. ''Inverting back the inversion of control or, Continuations versus page-centric programming'' SIGPLAN Notices 38(2), pp. 57–64, 2003.


External links

*
ACM ACM or A.C.M. may refer to: Aviation * AGM-129 ACM, 1990–2012 USAF cruise missile * Air chief marshal * Air combat manoeuvring or dogfighting * Air cycle machine * Arica Airport (Colombia) (IATA: ACM), in Arica, Amazonas, Colombia Computing * ...
SIGPLANbr>Workshop on Continuations 2011
at the ICFP.
Continuations for Curmudgeons
by Sam Ruby

by Dorai Sitaram features a nice chapter on continuations.

by Christian Tismer

* ttps://web.archive.org/web/20060501194520/http://www.brics.dk/~cw97/ On-line proceedings of the Second ACM SIGPLAN Workshop on Continuationsbr>Continuation, functions and jumpshttp://okmij.org/ftp/continuations/
by Oleg Kiselyov *https://wiki.haskell.org/Continuations
Rhino With ContinuationsContinuations in pure Java
from the RIFE web application framework
Debugging continuations in pure Java
from the RIFE web application framework

{{Formal semantics Control flow Articles with example Scheme (programming language) code