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@@ -23,7 +23,7 @@
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\def\racketEd{0}
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\def\pythonEd{1}
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-\def\edition{0}
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+\def\edition{1}
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% material that is specific to the Racket edition of the book
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\newcommand{\racket}[1]{{\if\edition\racketEd\color{olive}{#1}\fi}}
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@@ -838,24 +838,20 @@ defined in Figure~\ref{fig:r0-concrete-syntax}.
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\begin{minipage}{0.96\textwidth}
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{\if\edition\racketEd\color{olive}
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\[
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-\begin{array}{rcl}
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\begin{array}{rcl}
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\Exp &::=& \Int \mid \LP\key{read}\RP \mid \LP\key{-}\;\Exp\RP \mid \LP\key{+} \; \Exp\;\Exp\RP\\
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\LangInt{} &::=& \Exp
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\end{array}
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-\end{array}
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\]
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\fi}
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{\if\edition\pythonEd\color{purple}
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\[
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-\begin{array}{rcl}
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\begin{array}{rcl}
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\Exp &::=& \Int \mid \key{input\_int}\LP\RP \mid \key{-}\;\Exp \mid \Exp \; \key{+} \; \Exp\\
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\Stmt &::=& \key{print}\LP \Exp \RP \mid \Exp\\
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\LangInt{} &::=& \Stmt^{*}
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\end{array}
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-\end{array}
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\]
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\fi}
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@@ -1533,9 +1529,7 @@ def pe_add(r1, r2):
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def pe_exp(e):
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match e:
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case BinOp(left, Add(), right):
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- l = pe_exp(left)
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- r = pe_exp(right)
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- return pe_add(l, r)
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+ return pe_add(pe_exp(left), pe_exp(right))
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case UnaryOp(USub(), v):
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return pe_neg(pe_exp(v))
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case Constant(value):
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@@ -1590,7 +1584,8 @@ Appendix~\ref{appendix:utilities}.\\
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\chapter{Integers and Variables}
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\label{ch:Rvar}
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-This chapter is about compiling a subset of Racket to x86-64 assembly
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+This chapter is about compiling a subset of \racket{Racket}\python{Python}
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+to x86-64 assembly
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code~\citep{Intel:2015aa}. The subset, named \LangVar{}, includes
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integer arithmetic and local variable binding. We often refer to
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x86-64 simply as x86. The chapter begins with a description of the
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@@ -1607,20 +1602,22 @@ We hope to give enough hints that the well-prepared reader, together
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with a few friends, can implement a compiler from \LangVar{} to x86 in
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a couple weeks. To give the reader a feeling for the scale of this
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first compiler, the instructor solution for the \LangVar{} compiler is
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-approximately 500 lines of code.
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+approximately \racket{500}\python{300} lines of code.
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\section{The \LangVar{} Language}
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\label{sec:s0}
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\index{subject}{variable}
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-The \LangVar{} language extends the \LangInt{} language with variable
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-definitions. The concrete syntax of the \LangVar{} language is defined by
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-the grammar in Figure~\ref{fig:Rvar-concrete-syntax} and the abstract
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-syntax is defined in Figure~\ref{fig:Rvar-syntax}. The non-terminal
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-\Var{} may be any Racket identifier. As in \LangInt{}, \key{read} is a
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-nullary operator, \key{-} is a unary operator, and \key{+} is a binary
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-operator. Similar to \LangInt{}, the abstract syntax of \LangVar{} includes the
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-\key{Program} struct to mark the top of the program.
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+The \LangVar{} language extends the \LangInt{} language with
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+variables. The concrete syntax of the \LangVar{} language is defined
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+by the grammar in Figure~\ref{fig:Rvar-concrete-syntax} and the
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+abstract syntax is defined in Figure~\ref{fig:Rvar-syntax}. The
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+non-terminal \Var{} may be any Racket identifier. As in \LangInt{},
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+\key{read} is a nullary operator, \key{-} is a unary operator, and
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+\key{+} is a binary operator. Similar to \LangInt{}, the abstract
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+syntax of \LangVar{} includes the \racket{\key{Program}
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+ struct}\python{\key{Module} instance} to mark the top of the
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+program.
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%% The $\itm{info}$
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%% field of the \key{Program} structure contains an \emph{association
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%% list} (a list of key-value pairs) that is used to communicate
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@@ -1632,6 +1629,7 @@ exhibit several compilation techniques.
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\centering
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\fbox{
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\begin{minipage}{0.96\textwidth}
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+{\if\edition\racketEd\color{olive}
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\[
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\begin{array}{rcl}
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\Exp &::=& \Int{} \mid \CREAD{} \mid \CNEG{\Exp} \mid \CADD{\Exp}{\Exp}\\
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@@ -1639,6 +1637,16 @@ exhibit several compilation techniques.
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\LangVarM{} &::=& \Exp
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\end{array}
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\]
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+\fi}
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+{\if\edition\pythonEd\color{purple}
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+\[
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+\begin{array}{rcl}
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+ \Exp &::=& \Int \mid \key{input\_int}\LP\RP \mid \key{-}\;\Exp \mid \Exp \; \key{+} \; \Exp \mid \Var{} \\
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+ \Stmt &::=& \key{print}\LP \Exp \RP \mid \Exp \mid \Var\mathop{\key{=}}\Exp\\
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+ \LangVarM{} &::=& \Stmt^{*}
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+\end{array}
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+\]
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+\fi}
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\end{minipage}
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}
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\caption{The concrete syntax of \LangVar{}.}
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@@ -1649,6 +1657,7 @@ exhibit several compilation techniques.
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\centering
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\fbox{
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\begin{minipage}{0.96\textwidth}
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+{\if\edition\racketEd\color{olive}
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\[
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\begin{array}{rcl}
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\Exp &::=& \INT{\Int} \mid \READ{} \\
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@@ -1657,12 +1666,25 @@ exhibit several compilation techniques.
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\LangVarM{} &::=& \PROGRAM{\code{'()}}{\Exp}
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\end{array}
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\]
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+\fi}
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+{\if\edition\pythonEd\color{purple}
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+\[
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+\begin{array}{rcl}
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+\Exp{} &::=& \INT{\Int} \mid \READ{} \\
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+ &\mid& \NEG{\Exp} \mid \ADD{\Exp}{\Exp} \mid \VAR{\Var{}} \\
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+\Stmt{} &::=& \PRINT{\Exp} \mid \EXPR{\Exp} \\
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+ &\mid& \ASSIGN{\VAR{\Var}}{\Exp}\\
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+\LangInt{} &::=& \PROGRAM{}{\Stmt^{*}}
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+\end{array}
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+\]
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+\fi}
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\end{minipage}
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}
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\caption{The abstract syntax of \LangVar{}.}
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\label{fig:Rvar-syntax}
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\end{figure}
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+{\if\edition\racketEd\color{olive}
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Let us dive further into the syntax and semantics of the \LangVar{}
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language. The \key{let} feature defines a variable for use within its
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body and initializes the variable with the value of an expression.
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@@ -1676,6 +1698,26 @@ evaluates the body \code{(+ 10 x)}, producing $42$.
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\begin{lstlisting}
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(let ([x (+ 12 20)]) (+ 10 x))
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\end{lstlisting}
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+\fi}
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+%
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+{\if\edition\pythonEd\color{purple}
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+The \LangVar{} language adds variables and the assignment statement
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+to \LangInt{}. The assignment statement defines a variable for use by
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+later statements and initializes the variable with the value of an expression.
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+The abstract syntax for assignment is defined in
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+Figure~\ref{fig:Rvar-syntax}. The concrete syntax for assignment is
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+\begin{lstlisting}
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+|$\itm{var}$| = |$\itm{exp}$|
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+\end{lstlisting}
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+For example, the following program initializes \code{x} to $32$ and then
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+prints the result of \code{10 + x}, producing $42$.
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+\begin{lstlisting}
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+x = 12 + 20
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+print(10 + x)
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+\end{lstlisting}
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+\fi}
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+
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+{\if\edition\racketEd\color{olive}
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When there are multiple \key{let}'s for the same variable, the closest
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enclosing \key{let} is used. That is, variable definitions overshadow
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prior definitions. Consider the following program with two \key{let}'s
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@@ -1698,6 +1740,7 @@ $52$ then $10$, the following produces $42$ (not $-42$).
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\begin{lstlisting}
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(let ([x (read)]) (let ([y (read)]) (+ x (- y))))
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\end{lstlisting}
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+\fi}
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\subsection{Extensible Interpreters via Method Overriding}
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\label{sec:extensible-interp}
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@@ -1708,7 +1751,7 @@ object-oriented programming, that is, as a collection of methods
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inside of a class. Throughout this book we define many interpreters,
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one for each of the languages that we study. Because each language
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builds on the prior one, there is a lot of commonality between these
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-interpreters. We want to write down those common parts just once
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+interpreters. We want to write down the common parts just once
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instead of many times. A naive approach would be to have, for example,
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the interpreter for \LangIf{} handle all of the new features in that
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language and then have a default case that dispatches to the
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Jeremy Siek