Tidy up HO translation.

macros.tex

@@ -123,6 +123,9 @@
 \newcommand{\CompCat}{\CatName{Comp}}
 \newcommand{\UCompCat}{\CatName{UComp}}
 \newcommand{\UValCat}{\CatName{UVal}}
+\newcommand{\SCompCat}{\CatName{SComp}}
+\newcommand{\SValCat}{\CatName{SVal}}
+\newcommand{\SPatCat}{\CatName{SPat}}
 \newcommand{\ValCat}{\CatName{Val}}
 \newcommand{\VarCat}{\CatName{Var}}
 \newcommand{\ValTypeCat}{\CatName{VType}}

thesis.tex

@@ -860,8 +860,9 @@ given term.
 The function computes the set of free variables bottom-up. Most cases
 are homomorphic on the syntax constructors. The interesting cases are
 those constructs which feature term binders: lambda abstraction, let
-bindings, pair destructing, and case splitting. In each of those cases
+bindings, pair deconstructing, and case splitting. In each of those
-we subtract the relevant binder(s) from the set of free variables.
+cases we subtract the relevant binder(s) from the set of free
+variables.
 
 \subsection{Typing rules}
 \label{sec:base-language-type-rules}
@@ -1007,7 +1008,7 @@ application $V\,A$ is well-typed whenever the abstractor term $V$ has
 the polymorphic type $\forall \alpha^K.C$ and the type $A$ has kind
 $K$. This rule makes use of type substitution.
 %
-The \tylab{Split} rule handles typing of record destructing. When
+The \tylab{Split} rule handles typing of record deconstructing. When
 splitting a record term $V$ on some label $\ell$ binding it to $x$ and
 the remainder to $y$. The label we wish to split on must be present
 with some type $A$, hence we require that
@@ -1566,9 +1567,9 @@ effect handlers which are an alternative to deep effect handlers.
 %
 Programming with effect handlers is a dichotomy of \emph{performing}
 and \emph{handling} of effectful operations -- or alternatively a
-dichotomy of \emph{constructing} and \emph{destructing}. An operation
+dichotomy of \emph{constructing} and \emph{deconstructing}. An operation
 is a constructor of an effect without a predefined semantics. A
-handler destructs effects by pattern-matching on their operations. By
+handler deconstructs effects by pattern-matching on their operations. By
 matching on a particular operation, a handler instantiates the said
 operation with a particular semantics of its own choosing. The key
 ingredient to make this work in practice is \emph{delimited
@@ -2534,28 +2535,12 @@ operation clauses extract and convert the current resumption stack
 into a function using the $\Res$, and $\hforward$ augments the current
 resumption stack with the current continuation pair.
 %
-% Since we have only changed the representation of resumptions, the
-% translation of top-level programs remains the same.
 
 \subsection{Higher-order translation for deep effect handlers}
 \label{sec:higher-order-uncurried-deep-handlers-cps}
 %
 \begin{figure}
 %
-% \textbf{Static patterns and static lists}
-% %
-% \begin{syntax}
-% \slab{Static patterns} &\sP& ::= & \sk \scons \sP \mid \sks \\
-% \slab{Static lists} &\VS& ::= & V \scons \VS \mid \reflect V \\
-% \end{syntax}
-% %
-% \textbf{Reification}
-% %
-% \begin{equations}
-% \reify (V \scons \VS) &\defas& V \dcons \reify \VS \\
-% \reify \reflect V     &\defas& V \\
-% \end{equations}
-%
 \textbf{Values}
 %
 \begin{displaymath}
@@ -2573,7 +2558,7 @@ resumption stack with the current continuation pair.
 \textbf{Computations}
 %
 \begin{equations}
-\cps{-}  &:& \CompCat \to \UValCat^\ast \to \UCompCat\\
+\cps{-}  &:& \CompCat \to \SValCat^\ast \to \UCompCat\\
 \cps{V\,W}                                       &\defas& \slam \sks.\cps{V} \dapp \cps{W} \dapp \reify \sks \\
 \cps{V\,T}                                       &\defas& \slam \sks.\cps{V} \dapp \Record{} \dapp \reify \sks \\
 \cps{\Let\; \Record{\ell=x;y} = V \; \In \; N}  &\defas& \slam \sks.\Let\; \Record{\ell=x;y} = \cps{V} \; \In \; \cps{N} \sapp \sks \\
@@ -2594,19 +2579,6 @@ resumption stack with the current continuation pair.
 \cps{-} &:& \HandlerCat \to \UCompCat\\
 \cps{\{\Return \; x \mapsto N\}} &\defas& \dlam x\, ks.\Let\; (h \dcons ks') = ks \;\In\; \cps{N} \sapp \reflect ks'
 \\
-% \cps{\{(\ell \; p \; r \mapsto N_\ell)_{\ell \in \mathcal{L}}\}}
-% &\defas&
-% \bl
-% \dlam z \, ks.\Case \;z\; \{
-%       \bl
-%       (\ell~\Record{p, s} \mapsto \dLet\;r=\Fun\,s \;\dIn\; \cps{N_{\ell}} \sapp \reflect ks)_{\ell \in \mathcal{L}};\,
-%       y \mapsto \hforward \} \\
-%       \el \\
-% \el \\
-% \hforward &\defas& \bl
-%               \dLet\; (k' \dcons h' \dcons ks') = ks \;\dIn\; \\
-%               \Vmap\,(\dlam\Record{p, s}\,(k \dcons ks).k\,\Record{p, h' \dcons k' \dcons s}\,ks)\,y\,(h' \dcons ks') \\
-%               \el\\
 \cps{\{(\ell \; p \; r \mapsto N_\ell)_{\ell \in \mathcal{L}}\}}
      &\defas& \bl
                 \dlam \Record{z,\Record{p,rs}}\,ks.\Case \;z\; \{
@@ -2630,175 +2602,119 @@ resumption stack with the current continuation pair.
 \label{fig:cps-higher-order-uncurried}
 \end{figure}
 %
-% \begin{figure}[t]
+In the previous sections, we have step-wise refined the initial
-% \flushleft
+curried CPS translation for deep effect handlers
-% Values
+(Section~\ref{sec:first-order-curried-cps}) to be properly
-% \begin{equations}
+tail-recursive (Section~\ref{sec:first-order-uncurried-cps}) and to
-%   \cps{x}                    &\defas& x \\
+avoid yielding unnecessary dynamic administrative redexes for
-%   \cps{\lambda x.M}          &\defas& \dlam x\,\dhk.\Let\;\dRecord{fs,\dRecord{\vhret,\vhops}}\dcons \dhk' = \dhk\;\In\;\cps{M} \sapp (\sRecord{\reflect fs, \sRecord{\reflect \vhret, \reflect \vhops}} \scons \reflect \dhk') \\
+resumptions (Section~\ref{sec:first-order-explicit-resump}).
-%   \cps{\Lambda \alpha.M}     &\defas& \dlam z\,\dhk.\Let\;\dRecord{fs,\dRecord{\vhret,\vhops}}\dcons \dhk' = \dhk\;\In\;\cps{M} \sapp (\sRecord{\reflect fs, \sRecord{\reflect \vhret, \reflect \vhops}} \scons \reflect \dhk') \\
-%   \cps{\Rec\,g\,x.M} &\defas& \Rec\,g\,x\,\dhk.\Let\;\dRecord{fs,\dRecord{\vhret,\vhops}}\dcons \dhk' = \dhk\;\In\;\cps{M} \sapp (\sRecord{\reflect fs, \sRecord{\reflect \vhret, \reflect \vhops}} \scons \reflect \dhk') \\
-%   \multicolumn{3}{c}{
-%   \cps{\Record{}} \defas \Record{}
-%   \qquad
-%   \cps{\Record{\ell = \!\!V; W}} \defas \Record{\ell = \!\cps{V}; \cps{W}}
-%   \qquad
-%   \cps{\ell\,V} \defas \ell\,\cps{V}
-%   }
-% \end{equations}
-% % \begin{displaymath}
-% % \end{displaymath}
-% Computations
-% \begin{equations}
-% \cps{V\,W}                                       &\defas& \slam \shk.\cps{V} \dapp \cps{W} \dapp \reify \shk \\
-% \cps{V\,T}                                       &\defas& \slam \shk.\cps{V} \dapp \Record{} \dapp \reify \shk \\
-% \cps{\Let\; \Record{\ell=x;y} = V \; \In \; N}  &\defas& \slam \shk.\Let\; \Record{\ell=x;y} = \cps{V} \; \In \; \cps{N} \sapp \shk \\
-% \cps{\Case~V~\{\ell~x \mapsto M; y \mapsto N\}} &\defas&
-%   \slam \shk.\Case~\cps{V}~\{\ell~x \mapsto \cps{M} \sapp \shk; y \mapsto \cps{N} \sapp \shk\} \\
-% \cps{\Absurd~V}                                 &\defas& \slam \shk.\Absurd~\cps{V} \\
-% \end{equations}
-% \begin{equations}
-% \cps{\Return\,V} &=& \slam \shk.\kapp\;(\reify \shk)\;\cps{V} \\
-% \cps{\Let~x \revto M~\In~N} &=&
-%   \bl\slam \sRecord{\shf,  \sRecord{\svhret, \svhops}} \scons \shk.\\
-%   \qquad \cps{M} \sapp (\bl\sRecord{\reflect((\dlam x\,\dhk.\bl\Let\;\dRecord{fs,\dRecord{\vhret,\vhops}}\dcons k' = k\;\In\\
-%     \cps{N} \sapp (\sRecord{\reflect fs, \sRecord{\reflect \vhret, \reflect \vhops}} \scons \reflect k')) \dcons \reify\shf), \el\\
-%     \sRecord{\svhret, \svhops}} \scons \shk)\el
-%   \el\\
-% \cps{\Do\;\ell\;V} &\defas&
-%   \slam \sRecord{\shf, \sRecord{\svhret, \svhops}} \scons \shk.\,
-%          \reify\svhops \dapp \dRecord{\ell,\dRecord{\cps{V}, \dRecord{\reify \shf, \dRecord{\reify\svhret, \reify\svhops}} \dcons \dnil}} \dapp \reify \shk \\
-% \cps{\Handle^\depth \, M \; \With \; H} &\defas&
-% \slam \shk . \cps{M} \sapp (\sRecord{\snil, \cps{H}^\depth} \scons \shk) \\
-% \cps{H}^\depth &=& \sRecord{\reflect \cps{\hret}, \reflect \cps{\hops}^\depth}\\
-% \cps{\{\Return \; x \mapsto N\}} &\defas& \dlam x\,\dhk.\bl\Let\;\dRecord{fs,\dRecord{\vhret,\vhops}} \dcons k' = k\;\In\\\cps{N} \sapp (\sRecord{\reflect fs, \sRecord{\reflect \vhret, \reflect \vhops}} \scons \reflect k')\el
-% \\
-% \cps{\{(\ell \; p \; r \mapsto N_\ell)_{\ell \in \mathcal{L}}\}}^\depth
-% &\defas&
-% \bl
-% \dlam \dRecord{z,\dRecord{p,\dhkr}}\,\dhk.\bl
-%               \Case \;z\; \{
-%                 \begin{eqs}
-%                   (\ell &\mapsto& \Let\;r=\Res^\depth\,\dhkr\;\In\;  \\
-%                         &       & \Let\;\dRecord{fs,\dRecord{\vhret, \vhops}}\dcons k'=k\;\In\\
-%                         &       & \cps{N_{\ell}} \sapp (\sRecord{\reflect fs, \sRecord{\reflect \vhret, \reflect \vhops}} \scons \reflect \dhk'))_{\ell \in \mathcal{L}}\\
-%                   y     &\mapsto& \hforward((y, p, \dhkr), \dhk) \} \\
-%                 \end{eqs} \\
-%               \el \\
-% \el \\
-% \hforward((y, p, \dhkr), \dhk) &\defas& \bl
-%               \Let\; \dRecord{fs, \dRecord{\vhret, \vhops}} \dcons \dhk' = \dhk \;\In \\
-%               \Let\; rk' = \dRecord{fs, \dRecord{\vhret, \vhops}} \dcons \dhkr\;\In\\
-%               \vhops \dapp \dRecord{y,\dRecord{p, rk'}} \dapp \dhk' \\
-%               \el
-% \end{equations}
-
-% Top-level program
-% \begin{equations}
-% \pcps{M} &=& \cps{M} \sapp (\sRecord{\snil, \sRecord{\reflect \dlam x\,\dhk. x, \reflect \dlam \dRecord{z,\dRecord{p,rk}}\,\dhk.\Absurd~z}} \scons \snil) \\
-% \end{equations}
-
-% \caption{Higher-Order Uncurried CPS Translation of $\HCalc$}
-% \label{fig:cps-higher-order-uncurried}
-% \end{figure}
 %
-% We now adapt our uncurried CPS translation to a higher-order one-pass
+There is still one outstanding issue, namely, that the translation
-% CPS translation~\cite{DanvyF90} that partially evaluates
+yields static administrative redexes. In this section we will further
-% administrative redexes at translation time.
+refine the CPS translation to eliminate all static administrative
-% %
+redexes at translation time.
-% Following Danvy and Nielsen~\cite{DanvyN03}, we adopt a two-level
+%
-% lambda calculus notation to distinguish between \emph{static} lambda
+Specifically, we will adapt the translation to a higher-order one-pass
-% abstraction and application in the meta language and \emph{dynamic}
+CPS translation~\citep{DanvyF90} that partially evaluates
-% lambda abstraction and application in the target language.
+administrative redexes at translation time.
-% %
-% The idea is that redexes marked as static are reduced as part of the
-% translation (at compile time), whereas those marked as dynamic are
-% reduced at runtime.
-% %
-% The CPS translation is given in
-% Figure~\ref{fig:cps-higher-order-uncurried}.
-
-We now adapt the translation of Section~\ref{sec:pure-as-stack} to a
-higher-order one-pass CPS translation~\citep{DanvyF90} that partially
-evaluates administrative redexes at translation time.
 %
 Following \citet{DanvyN03}, we adopt a two-level lambda calculus
 notation to distinguish between \emph{static} lambda abstraction and
 application in the meta language and \emph{dynamic} lambda abstraction
-and application in the target language:
+and application in the target language. To disambiguate syntax
-{\color{blue}$\overline{\text{overline}}$} denotes a static syntax
+constructors in the respective calculi we mark static constructors
-constructor; {\color{red}$\underline{\text{underline}}$} denotes a
+with a {\color{blue}$\overline{\text{blue overline}}$}, whilst dynamic
-dynamic syntax constructor. The principal idea is that redexes marked
+constructors are marked with a
-as static are reduced as part of the translation (at compile time),
+{\color{red}$\underline{\text{red underline}}$}. The principal idea is
-whereas those marked as dynamic are reduced at runtime. To facilitate
+that redexes marked as static are reduced as part of the translation
-this notation we write application in both calculi with an infix
+(at compile time), whereas those marked as dynamic are reduced at
-``at'' symbol ($@$).
+runtime. To facilitate this notation we write application in both
+calculi with an infix ``at'' symbol ($@$).
 
 \paragraph{Static terms}
-Static constructs are marked in
-{\color{blue}$\overline{\text{static blue}}$}, and their redexes are
-reduced as part of the translation (at compile time).  We make use of
-static lambda abstractions, pairs, and lists. Reflection of dynamic
-language values into the static language is written as $\reflect V$.
 %
-We use $\shk$ for variables representing statically known
+As in the dynamic target language, we will represent continuations as
-continuations (frame stacks), $\shf$ for variables representing pure
+alternating lists of pure continuation functions and effect
-frame stacks, and $\chi$ for variables representing handlers.
+continuation functions. To ease notation we are going make use of
+pattern matching notation. The static meta language is generated by
+the following productions.
 %
-We let $\sV, \sW$ range over meta language values,
+\begin{syntax}
-$\sM$ range over static language expressions,
+  \slab{Static patterns} &\sP \in \SPatCat &::=& \sks \mid \sk \scons \sP\\
-and $\sP, \sQ$ over static language patterns.
+  \slab{Static values} & \sV, \sW \in \SValCat &::=& V \mid \reflect V \mid \sV \scons \sW \mid \slam \sP. \sM\\
+  \slab{Static computations} & \sM \in \SCompCat &::=& \sV \sapp \sW \mid \sV \dapp V \dapp W
+\end{syntax}
 %
-We use list and record pattern matching in the meta language, which
+The patterns comprise only static list deconstructing. We let $\sP$
-behaves as follows:
+range over static patterns.
 %
-\begin{displaymath}
+The static values comprise dynamic values, reflected dynamic values,
-  \ba{@{~}l@{~}l}
+static lists, and static lambda abstractions. We let $\sV, \sW$ range
-    &(\slam \sRecord{\sP, \sQ}.\,\sM) \sapp \sRecord{\sV, \sW}\\
+over meta language values; by convention we shall use variables $\sk$
-  = &(\slam \sP.\,\slam \sQ.\,\sM) \sapp \sV \sapp \sW\\
+to denote statically known pure continuations, $\sh$ to denote
-  = &(\slam (\sP \scons \sQ).\,\sM) \sapp (\sV \scons \sW)
+statically known effect continuations, and $\sks$ to denote statically
-  \ea
+known continuations.
-\end{displaymath}
 %
-Static language values, comprised of reflected values, pairs, and list
+We shall use $\sM$ to range over static computations, which comprise
-conses, are reified as dynamic language values $\reify \sV$ by
+static application and binary dynamic application of a static value to
-induction on their structure:
+two dynamic values.
+%
+Static computations are subject to the following equational axioms.
+%
+\begin{equations}
+  (\slam \sks. \sM) \sapp \sV &\defas& \sM[\sV/\sks]\\
+  (\slam \sk \scons \sks. \sM) \sapp (\sV \scons \sW) &\defas& (\slam \sks. \sM[\sV/\sk]) \sapp \sW\\
+\end{equations}
+%
+The first equation is static $\beta$-equivalence, it states that
+applying a static lambda abstraction with binder $\sks$ and body $\sM$
+to a static value $\sV$ is equal to substituting $\sV$ for $\sks$ in
+$\sM$. The second equation provides a means for applying a static
+lambda abstraction to a static list component-wise.
+%
+\dhil{What about $\eta$-equivalence?}
+
+Reflected static values are reified as dynamic language values
+$\reify \sV$ by induction on their structure.
 %
 \[
-  \ba{@{}l@{\qquad}c@{\qquad}r}
+  \ba{@{}l@{\qquad}c}
     \reify \reflect V \defas V
     &\reify (\sV \scons \sW) \defas \reify \sV \dcons \reify \sW
-    &\reify \sRecord{\sV, \sW} \defas \dRecord{\reify \sV, \reify \sW}
   \ea
 \]
 %
-We assume the static language is pure and hence respects the usual
+\dhil{Need to spell out that static pattern matching may induce dynamic (administrative) reductions}
-$\beta$ and $\eta$ equivalences.
+%
-
 \paragraph{Higher-order translation}
-The CPS translation is given in
+%
+The complete CPS translation is given in
 Figure~\ref{fig:cps-higher-order-uncurried}. In essence, it is the
-same as the CPS translation for deep and shallow handlers we described
+same as the refined first-order uncurried CPS translation, although
-in Section~\ref{sec:pure-as-stack}, albeit separated into static and
+the notation is slightly more involved due to the separation of static
-dynamic parts. A major difference that has a large cosmetic effect on
+and dynamic parts.
-the presentation of the translation is that we maintain the invariant
-that the statically known stack ($\sk$) always contains at least one
-frame, consisting of a triple
-$\sRecord{\reflect V_{fs}, \sRecord{\reflect V_{ret}, \reflect
-    V_{ops}}}$ of reflected dynamic pure frame stacks, return
-handlers, and operation handlers. Maintaining this invariant ensures
-that all translations are uniform in whether they appear statically
-within the scope of a handler or not, and this simplifies our
-correctness proof.  To maintain the invariant, any place where a
-dynamically known stack is passed in (as a continuation parameter
-$k$), it is immediately decomposed using a dynamic language $\Let$ and
-repackaged as a static value with reflected variable
-names. Unfortunately, this does add some clutter to the translation
-definition, as compared to the translations above. However, there is a
-payoff in the removal of administrative reductions at run time.
 %
-\dhil{Rewrite the above.}
+The translation on values is mostly homomorphic on the syntax
+constructors, except for $\lambda$- and $\Lambda$-abstractions which
+are translated in the exact same way, because the target calculus has
+no notion of types. As per usual continuation passing style practice,
+the translation of a lambda abstraction yields a dynamic binary lambda
+abstraction, where the second parameter is intended to be the
+continuation parameter. However, the translation slightly diverge from
+the usual practice in the translation of the body as the result of
+$\cps{M}$ is applied statically, rather than dynamically, to the
+(reflected) continuation parameter.
 %
+The reason is that the translation on computations is staged: for any
+given computation term the translation yields a static function, which
+can be applied to a static continuation to ultimately produce a
+$\UCalc$-computation term. This staging is key to eliminating static
+administrative redexes as any static function may perform static
+computation by manipulating its provided static continuation, as is
+for instance done in the translation of $\Let$.
+%
+\dhil{Spell out why this translation qualifies as `higher-order'.}
+
 Let us again revisit the example from
 Section~\ref{sec:first-order-curried-cps} to see that the higher-order
 translation eliminates the static redex at translation time.
@@ -2811,27 +2727,24 @@ translation eliminates the static redex at translation time.
 \end{equations}
 %
 In contrast with the previous translations, the image of this
-translation admits only a single dynamic reduction.
+translation admits only a single dynamic reduction (disregarding the
+dynamic administrative reductions arising from continuation
+construction and deconstruction).
 
 \subsubsection{Correctness}
 \label{sec:higher-order-cps-deep-handlers-correctness}
 
-To prove the correctness of our CPS translation
+We establish the correctness of the higher-order uncurried CPS
-(Theorem~\ref{thm:ho-simulation}), we first state several lemmas
+translation via a simulation result in style of
-describing how translated terms behave. In view of the invariant of
+Plotkin~\cite{Plotkin75} (Theorem~\ref{thm:ho-simulation}). However,
-the translation that we described above, we state each of these lemmas
+before we can state and prove this result, we first several auxiliary
-in terms of static continuation stacks where the shape of the top
+lemmas describing how translated terms behave. First, the higher-order
-element is always known statically, i.e., it is of the form
+CPS translation commutes with substitution.
-$\sRecord{\sV_{fs}, \sRecord{\sV_{ret},\sV_{ops}}} \scons
-\sW$. Moreover, the static values $\sV_{fs}$, $\sV_{ret}$, and
-$\sV_{ops}$ are all reflected dynamic terms (i.e., of the form
-$\reflect V$). This fact is used implicitly in our proofs, which are
-given in Appendix~\ref{sec:proofs}.
-
-First, the higher-order CPS translation commutes with substitution:
-\begin{lemma}[Substitution]\label{lem:subst}
 %
-  The CPS translation $\cps{-}$ commutes with substitution in value terms
+\begin{lemma}[Substitution]\label{lem:ho-cps-subst}
+  %
+  The higher-order uncurried CPS translation commutes with
+  substitution in value terms
   %
   \[
     \cps{W}[\cps{V}/x] = \cps{W[V/x]},
@@ -2840,33 +2753,55 @@ First, the higher-order CPS translation commutes with substitution:
   and with substitution in computation terms
   \[
        (\cps{M} \sapp (\sk \scons \sh \scons \sks))[\cps{V}/x]
-      = \cps{M[V/x]} \sapp (\sk \scons \sh \scons \sks)[\cps{V}/x].
+      = \cps{M[V/x]} \sapp (\sk \scons \sh \scons \sks)[\cps{V}/x],
   \]
   %
+  and with substitution in handler definitions
+  %
+  \begin{equations}
+     (\cps{\hret} \sapp (\sk \scons \sh \scons \sks))[\cps{V}/x]
+      &=& \cps{\hret[V/x]} \sapp (\sk \scons \sh \scons \sks)[\cps{V}/x],\\
+     (\cps{\hops} \sapp (\sk \scons \sh \scons \sks))[\cps{V}/x]
+      &=& \cps{\hops[V/x]} \sapp (\sk \scons \sh \scons \sks)[\cps{V}/x].
+  \end{equations}
 \end{lemma}
 %
 \begin{proof}
-  TODO\dots
+  Proof is by mutual induction on the structure of $W$, $M$, $\hret$,
+  and $\hops$.
 \end{proof}
 %
-In order to reason about the behaviour of the \semlab{Op} rule,
+It follows as a corollary that top-level substitution is well-behaved.
-which is defined in terms of an evaluation context, we extend the CPS
+%
+\begin{corollary}[Top-level substitution]
+  \[
+    \pcps{M}[\cps{V}/x] = \pcps{M[V/x]}.
+  \]
+\end{corollary}
+%
+\begin{proof}
+  Follows immediately by the definitions of $\pcps{-}$ and
+  Lemma~\ref{lem:ho-cps-subst}.
+\end{proof}
+%
+In order to reason about the behaviour \semlab{Op} rule, which is
+defined in terms of an evaluation context, we need to extend the CPS
 translation to evaluation contexts.
 %
-\begin{displaymath}
+\begin{equations}
-\ba{@{}r@{~}c@{~}r@{~}l@{}}
+\cps{-}                             &:& \EvalCat \to \SValCat\\
-\cps{[~]}                           &=& \slam \sks.           &\sks \\
+\cps{[~]}                           &\defas& \slam \sks.\sks \\
-\cps{\Let\; x \revto \EC \;\In\; N} &=& \slam \sk \scons \sks.&\cps{\EC} \sapp ((\dlam x\,ks.\cps{N} \sapp (k \scons \reflect ks)) \scons \sks) \\
+\cps{\Let\; x \revto \EC \;\In\; N} &\defas& \slam \sk \scons \sks.\cps{\EC} \sapp ((\dlam x\,ks.\cps{N} \sapp (k \scons \reflect ks)) \scons \sks) \\
-\cps{\Handle\; \EC \;\With\; H}     &=& \slam \sks.           &\cps{\EC} \sapp (\cps{\hret} \scons \cps{\hops} \scons \sks) \\
+\cps{\Handle\; \EC \;\With\; H}     &\defas& \slam \sks. \cps{\EC} \sapp (\cps{\hret} \scons \cps{\hops} \scons \sks)
-\ea
+\end{equations}
-\end{displaymath}
 %
 The following lemma is the characteristic property of the CPS
 translation on evaluation contexts.
 %
-This allows us to focus on the computation contained within
+It provides a means for decomposing an evaluation context, such that
-an evaluation context.
+we can focus on the computation contained within the evaluation
-
+context.
+%
 \begin{lemma}[Decomposition]
 \label{lem:decomposition}
 %
@@ -2877,35 +2812,41 @@ an evaluation context.
 \end{lemma}
 %
 \begin{proof}
-  TODO\dots
+  Proof by structural induction on the evaluation context $\EC$.
 \end{proof}
 %
-Though we have eliminated the static administrative redexes, we are
+Even though we have eliminated the static administrative redexes, we
-still left with one form of administrative redex that cannot be
+still need to account for the dynamic administrative redexes that
-eliminated statically because it only appears at run-time. These arise
+arise from pattern matching against a reified continuation. To
-from pattern matching against a reified stack of continuations and are
+properly account for these administrative redexes it is convenient to
-given by the $\usemlab{SplitList}$ rule.
+treat list pattern matching as a primitive in $\UCalc$, therefore we
-
+introduce a new reduction rule $\usemlab{SplitList}$ in $\UCalc$.
+%
 \begin{reductions}
 \usemlab{SplitList} & \Let\; (k \dcons ks) = V \dcons W \;\In\; M &\reducesto& M[V/k, W/ks] \\
 \end{reductions}
 %
-This is isomorphic to the \usemlab{Split} rule, but we now treat lists
+Note this rule is isomorphic to the \usemlab{Split} rule with lists
-and \usemlab{SplitList} as distinct from pairs, unit, and
+encoded as right nested pairs using unit to denote nil.
-\usemlab{Split} in the higher-order translation so that we can
-properly account for administrative reduction.
 %
 We write $\areducesto$ for the compatible closure of
 \usemlab{SplitList}.
 
-By definition, $\reify \reflect V = V$, but we also need to reason
+We also need to be able to reason about the computational content of
-about the inverse composition.
+reflection after reification. By definition we have that
+$\reify \reflect V = V$, the following lemma lets us reason about the
+inverse composition.
 %
 \begin{lemma}[Reflect after reify]
 \label{lem:reflect-after-reify}
-$\cps{M} \sapp (V_1 \scons \dots V_n \scons \reflect \reify \VS)
+%
-  \areducesto^*
+Reflection after reification may give rise to dynamic administrative
-    \cps{M} \sapp (V_1 \scons \dots V_n \scons \VS)$
+reductions, i.e.
+%
+\[
+\cps{M} \sapp (V_1 \scons \dots V_n \scons \reflect \reify \sV)
+  \areducesto^* \cps{M} \sapp (V_1 \scons \dots V_n \scons \sV)
+\]
 \end{lemma}
 %
 \begin{proof}
@@ -2916,48 +2857,45 @@ We next observe that the CPS translation simulates forwarding.
 %
 \begin{lemma}[Forwarding]
 \label{lem:forwarding}
-If $\ell \notin dom(H_1)$ then:
+If $\ell \notin dom(H_1)$ then
 %
-\begin{displaymath}
+\[
-    \cps{\hops_1} \dapp \ell\,\Record{U, V} \dapp (V_2 \dcons \cps{\hops_2} \dcons W)
+    \cps{\hops_1} \dapp \Record{\ell,\Record{U, V}} \dapp (V_2 \dcons \cps{\hops_2} \dcons W)
 \reducesto^+
-    \cps{\hops_2} \dapp \ell\,\Record{U, \cps{\hops_2} \dcons V_2 \dcons V} \dapp W
+    \cps{\hops_2} \dapp \Record{\ell,\Record{U, \cps{\hops_2} \dcons V_2 \dcons V}} \dapp W
-\end{displaymath}
+\]
+%
 \end{lemma}
 %
 \begin{proof}
-  TODO\dots
+  Proof by direct calculation.
 \end{proof}
 %
 Now we show that the translation simulates the \semlab{Op}
 rule.
-
 %
 \begin{lemma}[Handling]
 \label{lem:handle-op}
-If $\ell \notin BL(\EC)$ and $\hell = \{\ell\,p\,r \mapsto N_\ell\}$ then:
+If $\ell \notin BL(\EC)$ and $\hell = \{\ell\,p\,r \mapsto N_\ell\}$ then
 %
 \begin{displaymath}
 \bl
-\cps{\Do\;\ell\;V} \sapp (\cps{\EC} \sapp (\cps{\hret} \scons \cps{\hops} \scons \VS)) \reducesto^+\areducesto^* \\
+\cps{\Do\;\ell\;V} \sapp (\cps{\EC} \sapp (\cps{\hret} \scons \cps{\hops} \scons \sV)) \reducesto^+\areducesto^* \\
 \quad
-    (\cps{N_\ell} \sapp \VS)[\cps{V}/p, (\lambda y\,ks.\cps{\Return\;y} \sapp (\cps{\EC} \sapp (\cps{\hret} \scons \cps{\hops} \scons \reflect ks)))/r] \\
+    (\cps{N_\ell} \sapp \sV)[\cps{V}/p, (\lambda y\,ks.\cps{\Return\;y} \sapp (\cps{\EC} \sapp (\cps{\hret} \scons \cps{\hops} \scons \reflect ks)))/r] \\
 \el
 \end{displaymath}
 \end{lemma}
 %
-%
 \begin{proof}
 Follows from Lemmas~\ref{lem:decomposition},
 \ref{lem:reflect-after-reify}, and \ref{lem:forwarding}.
 \end{proof}
 %
-We now turn to our main result which is a simulation result in style
+Finally, we have the ingredients to state and prove the simulation
-of Plotkin~\cite{Plotkin75}. The theorem shows that the only extra
+result. The following theorem shows that the only extra behaviour
-behaviour exhibited by a translated term is the bureaucracy of
+exhibited by a translated term is the bureaucracy of deconstructing
-deconstructing the continuation stack.
+the continuation stack.
-%
-
 %
 \begin{theorem}[Simulation]
 \label{thm:ho-simulation}
@@ -2965,25 +2903,23 @@ If $M \reducesto N$ then $\pcps{M} \reducesto^+ \areducesto^* \pcps{N}$.
 \end{theorem}
 %
 \begin{proof}
-  TODO\dots
+  Proof is by case analysis on the reduction relation using Lemmas
+  \ref{lem:decomposition}--\ref{lem:handle-op}. The \semlab{Op} case
+  follows from Lemma~\ref{lem:handle-op}.
 \end{proof}
 %
-The proof is by case analysis on the reduction relation using Lemmas
+% In common with most CPS translations, full abstraction does not
-\ref{lem:decomposition}--\ref{lem:handle-op}. The \semlab{Op}
+% hold. However, as our semantics is deterministic it is straightforward
-case follows from Lemma~\ref{lem:handle-op}.
+% to show a backward simulation result.
-
+% %
-In common with most CPS translations, full abstraction does not
+% \begin{corollary}[Backwards simulation]
-hold. However, as our semantics is deterministic it is straightforward
+% If $\pcps{M} \reducesto^+ \areducesto^* V$ then there exists $W$ such that
-to show a backward simulation result.
+% $M \reducesto^* W$ and $\pcps{W} = V$.
-%
+% \end{corollary}
-\begin{corollary}[Backwards simulation]
+% %
-If $\pcps{M} \reducesto^+ \areducesto^* V$ then there exists $W$ such that
+% \begin{proof}
-$M \reducesto^* W$ and $\pcps{W} = V$.
+%   TODO\dots
-\end{corollary}
+% \end{proof}
-%
-\begin{proof}
-  TODO\dots
-\end{proof}
 %
 \chapter{Abstract machine semantics}