[macros, stmt] Introduce macro \bnfindent and change bnftab to simplebnf.

Indentation that was previously achieved with tabbing is now done with
\bnfindent. One particularly tricky case of aligned comments required
the use of zero-width boxes for alignment.

Author: tkoeppe

source/macros.tex

@@ -428,6 +428,7 @@
 \setlength{\BnfRest}{2\BnfIndent}
 \newcommand{\BnfNontermshape}{\small\rmfamily\itshape}
 \newcommand{\BnfTermshape}{\small\ttfamily\upshape}
+\newcommand{\bnfindent}{\hspace*{\bnfindentfirst}}
 
 \newenvironment{bnfbase}
  {

source/statements.tex

@@ -296,35 +296,27 @@
 
 \pnum
 An \tcode{if} statement of the form
-
-\begin{ncbnf}
+\begin{ncsimplebnf}
 \terminal{if \opt{constexpr} (} init-statement condition \terminal{)} statement
-\end{ncbnf}
-
+\end{ncsimplebnf}
 is equivalent to
-
-\begin{ncbnftab}
+\begin{ncsimplebnf}
 \terminal{\{}\br
-\>init-statement\br
-\>\terminal{if \opt{constexpr} (} condition \terminal{)} statement\br
+\bnfindent init-statement\br
+\bnfindent \terminal{if \opt{constexpr} (} condition \terminal{)} statement\br
 \terminal{\}}
-\end{ncbnftab}
-
+\end{ncsimplebnf}
 and an \tcode{if} statement of the form
-
-\begin{ncbnf}
+\begin{ncsimplebnf}
 \terminal{if \opt{constexpr} (} init-statement condition \terminal{)} statement \terminal{else} statement
-\end{ncbnf}
-
+\end{ncsimplebnf}
 is equivalent to
-
-\begin{ncbnftab}
+\begin{ncsimplebnf}
 \terminal{\{}\br
-\>init-statement\br
-\>\terminal{if \opt{constexpr} (} condition \terminal{)} statement \terminal{else} statement\br
+\bnfindent init-statement\br
+\bnfindent \terminal{if \opt{constexpr} (} condition \terminal{)} statement \terminal{else} statement\br
 \terminal{\}}
-\end{ncbnftab}
-
+\end{ncsimplebnf}
 except that names declared in the \grammarterm{init-statement} are in
 the same declarative region as those declared in the
 \grammarterm{condition}.
@@ -400,20 +392,16 @@
 
 \pnum
 A \tcode{switch} statement of the form
-
-\begin{ncbnf}
+\begin{ncsimplebnf}
 \terminal{switch (} init-statement condition \terminal{)} statement
-\end{ncbnf}
-
+\end{ncsimplebnf}
 is equivalent to
-
-\begin{ncbnftab}
+\begin{ncsimplebnf}
 \terminal{\{}\br
-\>init-statement\br
-\>\terminal{switch (} condition \terminal{)} statement\br
+\bnfindent init-statement\br
+\bnfindent \terminal{switch (} condition \terminal{)} statement\br
 \terminal{\}}
-\end{ncbnftab}
-
+\end{ncsimplebnf}
 except that names declared in the \grammarterm{init-statement} are in
 the same declarative region as those declared in the
 \grammarterm{condition}.%
@@ -513,23 +501,20 @@
 \grammarterm{statement}. A \tcode{while} statement whose \grammarterm{condition}
 is an initialized declaration of some variable \tcode{t}
 is equivalent to
-
-\begin{ncbnftab}
+\begin{ncsimplebnf}
 \terminal{label:}\br
-\terminal{\{}\>\>\>// start of condition scope\br
-\>condition \terminal{;}\>\>// declares \terminal{t}\br
-\>\terminal{if (t) \{}\br
-\>\>statement\br
-\>\>\terminal{goto label;}\br
-\>\terminal{\}}\br
-\terminal{\}}\>\>\>// end of condition scope
-\end{ncbnftab}
-
+\makebox[0pt][l]{\terminal{\{}}\bnfindent\bnfindent\bnfindent\bnfindent// start of condition scope\br
+\bnfindent\makebox[0pt][l]{condition \terminal{;}}\bnfindent\bnfindent\bnfindent// declares \terminal{t}\br
+\bnfindent \terminal{if (t) \{}\br
+\bnfindent\bnfindent statement\br
+\bnfindent\bnfindent \terminal{goto label;}\br
+\bnfindent \terminal{\}}\br
+\makebox[0pt][l]{\terminal{\}}}\bnfindent\bnfindent\bnfindent\bnfindent// end of condition scope
+\end{ncsimplebnf}
 \begin{note}
 The variable created in the condition is destroyed and created with each
 iteration of the loop.
 \begin{example}
-
 \begin{codeblock}
 struct A {
   int val;
@@ -543,7 +528,6 @@
   i = 0;
 }
 \end{codeblock}
-
 In the while-loop, the constructor and destructor are each called twice,
 once for the condition that succeeds and once for the condition that
 fails.
@@ -567,23 +551,19 @@
 
 \pnum
 The \tcode{for} statement
-
-\begin{ncbnf}
+\begin{ncsimplebnf}
 \terminal{for (} init-statement \opt{condition} \terminal{;} \opt{expression} \terminal{)} statement
-\end{ncbnf}
-
+\end{ncsimplebnf}
 is equivalent to
-
-\begin{ncbnftab}
+\begin{ncsimplebnf}
 \terminal{\{}\br
-\>init-statement\br
-\>\terminal{while (} condition \terminal{) \{}\br
-\>\>statement\br
-\>\>expression \terminal{;}\br
-\>\terminal{\}}\br
+\bnfindent init-statement\br
+\bnfindent \terminal{while (} condition \terminal{) \{}\br
+\bnfindent\bnfindent statement\br
+\bnfindent\bnfindent expression \terminal{;}\br
+\bnfindent \terminal{\}}\br
 \terminal{\}}
-\end{ncbnftab}
-
+\end{ncsimplebnf}
 except that names declared in the \grammarterm{init-statement} are in
 the same declarative region as those declared in the
 \grammarterm{condition}, and except that a
@@ -629,28 +609,23 @@
 
 \pnum
 The range-based \tcode{for} statement
-
-\begin{ncbnf}
+\begin{ncsimplebnf}
 \terminal{for (} \opt{init-statement} for-range-declaration \terminal{:} for-range-initializer \terminal{)} statement
-\end{ncbnf}
-
+\end{ncsimplebnf}
 is equivalent to
-
-\begin{ncbnftab}
+\begin{ncsimplebnf}
 \terminal{\{}\br
-\>\opt{init-statement}\br
-\>\terminal{auto \&\&__range =} for-range-initializer \terminal{;}\br
-\>\terminal{auto __begin =} begin-expr \terminal{;}\br
-\>\terminal{auto __end =} end-expr \terminal{;}\br
-\>\terminal{for ( ; __begin != __end; ++__begin ) \{}\br
-\>\>for-range-declaration \terminal{= *__begin;}\br
-\>\>statement\br
-\>\terminal{\}}\br
+\bnfindent \opt{init-statement}\br
+\bnfindent \terminal{auto \&\&__range =} for-range-initializer \terminal{;}\br
+\bnfindent \terminal{auto __begin =} begin-expr \terminal{;}\br
+\bnfindent \terminal{auto __end =} end-expr \terminal{;}\br
+\bnfindent \terminal{for ( ; __begin != __end; ++__begin ) \{}\br
+\bnfindent\bnfindent for-range-declaration \terminal{= *__begin;}\br
+\bnfindent\bnfindent statement\br
+\bnfindent \terminal{\}}\br
 \terminal{\}}
-\end{ncbnftab}
-
+\end{ncsimplebnf}
 where
-
 \begin{itemize}
 \item
 if the \grammarterm{for-range-initializer} is an \grammarterm{expression},