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@ -2097,16 +2097,16 @@ Shallow handlers can be used to simulate control0 and prompt0. |
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\slab{Resume} & \Continue~\cont_{\EC}~V &\reducesto& \EC[V] |
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\end{reductions} |
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\subsection{Second-class control operators} |
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Coroutines, async/await, generators/iterators, amb. |
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% \subsection{Second-class control operators} |
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% Coroutines, async/await, generators/iterators, amb. |
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Backtracking: Amb~\cite{McCarthy63}. |
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% Backtracking: Amb~\cite{McCarthy63}. |
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Coroutines~\cite{DahlDH72} as introduced by Simula |
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67~\cite{DahlMN68}. The notion of coroutines was coined by Melvin |
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Conway, who used coroutines as a code idiom in assembly |
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programs~\cite{Knuth97}. Canonical reference for implementing |
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coroutines with call/cc~\cite{HaynesFW86}. |
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% Coroutines~\cite{DahlDH72} as introduced by Simula |
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% 67~\cite{DahlMN68}. The notion of coroutines was coined by Melvin |
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% Conway, who used coroutines as a code idiom in assembly |
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% programs~\cite{Knuth97}. Canonical reference for implementing |
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% coroutines with call/cc~\cite{HaynesFW86}. |
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\section{Programming continuations} |
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%Blind vs non-blind backtracking. Engines. Web |
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@ -2118,17 +2118,65 @@ jumps, such as \citeauthor{Landin98}'s modelling of \Algol{} labels |
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and gotos using the J |
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operator~\cite{Landin65,Landin65a,Landin98,Reynolds93}. |
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Backtracking is another early and prominent use of |
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continuations. \citet{Burstall69} used the J operator to implement a |
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backtracking mechanism to facilitate tree-based search. |
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Backtracking is another early and prominent use of continuations. For |
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example, \citet{Burstall69} used the J operator to implement a |
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heuristic-driven search procedure with continuation-backed |
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backtracking for tree-based search. |
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% |
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Somewhat related to backtracking, \citet{FriedmanHK84} posed the |
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\emph{devils and angels problem} as an example that has no direct |
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solution in a programming language without first-class control. Any |
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solution to the devils and angels problem involves extensive |
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manipulation of control to jump both backwards and forwards to resume |
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computation. |
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If the reader ever find themselves in a quiz show asked to single out |
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a canonical example of continuation use, then implementation of |
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cooperative concurrency would be a qualified guess. Various forms of |
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coroutines as continuations occur so frequently in the literature and |
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in the wild that they have become routine. |
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% |
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\citet{HaynesFW86} published one of the first implementations of |
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coroutines using first-class control. \citet{HiebD90} demonstrated how |
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to implement engines. An engine is a kind of scheduler for |
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computations running on a time budget~\cite{HaynesF84}. |
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% |
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Various other forms of schedulers were developed by \citet{GanzFW99}. |
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Continuations have also been used in meta-programming to speed up |
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partial evaluation and |
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multi-staging~\cite{LawallD94,KameyamaKS11,OishiK17,Yallop17}. Let |
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insertion is a canonical example of use of continuations in |
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multi-staging~\cite{Yallop17}. |
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Meta-programming~\cite{LawallD94,KameyamaKS11,OishiK17,Yallop17}. |
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The aforementioned applications of continuations is by no means |
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exhaustive, however, the diverse application spectrum underlines the |
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versatility of continuations. |
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\section{Constraining continuations} |
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\citet{FriedmanH85} argued in favour of constraining the power of |
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continuations~\cite{HaynesF87}. Although, they were concerned with |
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callcc and undelimited continuations many of their arguments are |
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applicable to other control operators and delimited continuations. |
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For example callec is a variation of callcc where the continuation |
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only can be invoked during the dynamic extent of |
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callec~\cite{Flatt20}. |
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Dynamic-wind\dots |
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To avoid resource leakage the implementation of effect handlers in |
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Multicore OCaml provides both a \emph{continue} primitive for |
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continuing a given continuation and a \emph{discontinue} primitive for |
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aborting a given continuation~\cite{DolanWSYM15,DolanEHMSW17}. The |
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latter throws an exception at the operation invocation site to clean |
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up resources. |
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% |
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A similar approached is used by \citet{Fowler19}, who uses a |
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substructural type system to statically enforce the use of |
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continuations, either by means of a continue or a discontinue. |
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\section{Implementing continuations} |
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Table~\ref{tbl:ctrl-operators-impls} lists some programming languages |
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with support for first-class control operators and their |
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@ -2178,7 +2226,7 @@ implementation strategies. |
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\paragraph{Continuation passing style} |
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\paragraph{Interpreter} |
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\paragraph{Abstract and virtual machines} |
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\paragraph{Segmented stacks} |
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