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@ -2254,7 +2254,7 @@ implementation strategies. |
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\hline |
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Effekt & Lexical effect handlers & ??\\ |
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Effekt & Lexical effect handlers & ??\\ |
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\hline |
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Frank & N-ary effect handlers & Abstract machine \\ |
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Frank & N-ary effect handlers & CEK machine \\ |
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\hline |
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\hline |
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Gauche & callcc, shift/reset & Virtual machine \\ |
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Gauche & callcc, shift/reset & Virtual machine \\ |
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@ -2272,8 +2272,8 @@ implementation strategies. |
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Racket & callcc, \textCallcomc{}, cupto, fcontrol, control/prompt, shift/reset, splitter, spawn & Segmented stacks\\ |
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Racket & callcc, \textCallcomc{}, cupto, fcontrol, control/prompt, shift/reset, splitter, spawn & Segmented stacks\\ |
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\hline |
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Rhino JavaScript & JI & Interpreter \\ |
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% Rhino JavaScript & JI & Interpreter \\ |
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% \hline |
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Scala & shift/reset & CPS\\ |
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Scala & shift/reset & CPS\\ |
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\hline |
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SML/NJ & callcc & CPS\\ |
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SML/NJ & callcc & CPS\\ |
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@ -2339,24 +2339,70 @@ slight variation of segmented stacks optimised for one-shot |
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continuations, which has been adapted by Multicore |
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continuations, which has been adapted by Multicore |
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OCaml~\cite{DolanEHMSW17}. |
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OCaml~\cite{DolanEHMSW17}. |
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\dhil{TODO: abstract machines} |
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Continuation passing style (CPS) is a particular idiomatic notation |
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for programs, where every aspect of control flow is made explicit, |
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which makes it a good fit for implementing control abstractions. |
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Full stack copying and segmented stacks both depend on being able to |
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manipulate the stack directly. This is seldom possible if the language |
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implementer do not have control over the target runtime, |
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e.g. compilation to JavaScript. However, it is possible to emulate |
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stack copying and segmented stacks in lieu of direct stack access. For |
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example, \citet{PettyjohnCMKF05} describe a technique that emulates |
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stack copying by piggybacking on the facile stack inception facility |
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provided by exception handlers in order to lazily reify the control |
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stack. |
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% |
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% |
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Using trampolines CPS is even a viable strategy in environments that |
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lack proper tail calls such as JavaScript~\cite{GanzFW99}. |
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% \paragraph{Continuation marks} |
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% \paragraph{Continuation passing style} |
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% \paragraph{Abstract and virtual machines} |
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% \paragraph{Segmented stacks} |
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% \paragraph{Stack copying} |
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\citet{KumarBD98} emulated segmented stacks via threads. Each thread |
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has its own local stack, and as such, a collection of threads |
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effectively models segmented stacks. To actually implement |
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continuations as threads \citeauthor{KumarBD98} also made use of |
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standard synchronisation primitives. |
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% |
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The advantage of these techniques is that they are generally |
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applicable and portable. The disadvantage is the performance overhead |
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induced by emulation. |
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Abstract and virtual machines are a form of full machine emulation. An |
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abstract machine is an idealised machine. Abstract machines, such as |
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the CEK machine~\cite{FelleisenF86}, are attractive because they |
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provide a suitably high-level framework for defining language |
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semantics in terms of control string manipulations, whilst admitting a |
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direct implementation. |
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% |
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We will discuss abstract machines in more detail in |
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Chapter~\ref{ch:abstract-machine}. |
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% |
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The term virtual machine typically connotes an abstract machine that |
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works on a byte code representation of programs, whereas the default |
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connotation of abstract machine is a machine that works on a rich |
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abstract syntax tree representation of programs. |
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% \citeauthor{Landin64}'s SECD machine was the |
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% first abstract machine for evaluating $\lambda$-calculus |
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% terms~\cite{Landin64,Danvy04}. |
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% |
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% Either machine model has an explicit representation of the control |
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% state in terms of an environment and a control string. Thus either machine can to the |
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% interpretative overhead. |
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The disadvantage of abstract machines is their interpretative |
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overhead, although, techniques such as just-in-time compilation can be |
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utilised to reduce this overhead. |
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Continuation passing style (CPS) is a canonical implementation |
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strategy for continuations --- the word `continuation' even feature in |
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its name. |
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% |
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CPS is a particular idiomatic notation for programs, where every |
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function takes an additional argument, the current continuation, as |
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input and every function call appears in tail position. Consequently, |
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every aspect of control flow is made explicit, which makes CPS a good |
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fit for implementing control abstraction. In classic CPS the |
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continuation argument is typically represented as a heap allocated |
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closure~\cite{Appel92}, however, as we shall see in |
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Chapter~\ref{ch:cps} richer representations of continuations are |
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possible. |
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% |
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At first thought it may seem that CPS will not work well in |
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environments that lack proper tail calls such as JavaScript. However, |
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the contrary is true, because the stackless nature of CPS means it can |
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readily be implemented with a trampoline~\cite{GanzFW99}. Alas, at the |
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cost of the indirection induced by the trampoline. |
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\part{Design} |
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\part{Design} |
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@ -8391,6 +8437,7 @@ then in the image $\cps{M}\,k \reducesto^\ast k\,\cps{V}$. |
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\paragraph{Partial evaluation} |
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\paragraph{Partial evaluation} |
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\chapter{Abstract machine semantics} |
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\chapter{Abstract machine semantics} |
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\label{ch:abstract-machine} |
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\dhil{The text is this chapter needs to be reworked} |
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\dhil{The text is this chapter needs to be reworked} |
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In this chapter we develop an abstract machine that supports deep and |
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In this chapter we develop an abstract machine that supports deep and |
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