starting on explicate

book.tex

@@ -7789,7 +7789,7 @@ list of \code{passes} and then run the script to test your compiler.
 
 \racket{Recall that the purpose of \code{explicate\_control} is to
   make the order of evaluation explicit in the syntax of the program.
-  With the addition of \key{if} this get more interesting.}
+  With the addition of \key{if} this gets more interesting.}
 %
 The \code{explicate\_control} pass translates from \LangIf{} to \LangCIf{}.
 %
@@ -7847,8 +7847,9 @@ above example would be as follows.
 \end{lstlisting}
 \end{minipage}
 \end{center}
-However, if we take context into account we can do better and reduce
-the use of \key{cmpq} instructions for accessing the EFLAG register.
+Notice that the three instructions starting with \code{setl} are
+redundant: the conditional jump could come immediately after the first
+\code{cmpq}. 
 
 Our goal will be to compile \key{if} expressions so that the relevant
 comparison instruction appears directly before the conditional jump.
@@ -7894,7 +7895,7 @@ print(((y + 2) if x == 0 else (y + 10)) \
 \end{center}
 Unfortunately, this approach duplicates the two branches from the
 outer \code{if} and a compiler must never duplicate code!  After all,
-the two branches could have been very large expressions.
+the two branches could be very large expressions.
 
 We need a way to perform the above transformation but without
 duplicating code. That is, we need a way for different parts of a
@@ -7908,7 +7909,7 @@ label the code for each branch and insert jumps in all the places that
 need to execute the branch.
 %
 Likewise, our language \LangCIf{} provides the ability to label a
-sequence of code and to jump to a label via \code{goto}.
+sequence of statements and to jump to a label via \code{goto}.
 %
 %% In particular, we use a standard program representation called a
 %% \emph{control flow graph} (CFG), due to Frances Elizabeth
@@ -7929,7 +7930,7 @@ sequence of code and to jump to a label via \code{goto}.
 {\if\edition\racketEd        
 %
 Recall that in Section~\ref{sec:explicate-control-Lvar} we implement
-\code{explicate\_control} for \LangVar{} using two mutually recursive
+\code{explicate\_control} for \LangVar{} using two recursive
 functions, \code{explicate\_tail} and \code{explicate\_assign}.  The
 former function translates expressions in tail position whereas the
 later function translates expressions on the right-hand-side of a
@@ -7937,9 +7938,9 @@ later function translates expressions on the right-hand-side of a
 have a new kind of position to deal with: the predicate position of
 the \key{if}. We need another function, \code{explicate\_pred}, that
 decides how to compile an \key{if} by analyzing its predicate.  So
-\code{explicate\_pred} takes an \LangIf{} expression and two \LangCIf{}
-tails for the then-branch and else-branch and outputs a tail.  In the
-following paragraphs we discuss specific cases in the
+\code{explicate\_pred} takes an \LangIf{} expression and two
+\LangCIf{} tails for the then-branch and else-branch and outputs a
+tail.  In the following paragraphs we discuss specific cases in the
 \code{explicate\_tail}, \code{explicate\_assign}, and
 \code{explicate\_pred} functions.
 %