[macros] Avoid page break between example and codeblock introducers

if they are immediately following each other.

Author: jensmaurer

source/macros.tex

@@ -267,7 +267,7 @@
 \newcommand{\leftshift}[1]{\ensuremath{\mathbin{\mathsf{lshift}_{#1}}}}
 
 %% Notes and examples
-\newcommand{\noteintro}[1]{[\textit{#1}:}
+\newcommand{\noteintro}[1]{[\textit{#1}: }
 \newcommand{\noteoutro}[1]{\textit{\,---\,#1}\kern.5pt]}
 
 % \newnoteenvironment{ENVIRON}{BEGIN TEXT}{END TEXT}
@@ -278,7 +278,7 @@
 \newcommand{\newnoteenvironment}[3]{
 \newsubclausecounter{#1}
 \newenvironment{#1}
-{\def\noteend{#3}\par\small\stepcounter{#1}\noteintro{#2}}
+{\def\noteend{#3}\par\small\stepcounter{#1}\noteintro{#2}\hbox to 0pt{}\ignorespaces}
 {\noteoutro{\noteend}\par}
 }
 
@@ -462,9 +462,10 @@
 % Our usual abbreviation for 'listings'.  Comments are in
 % italics.  Arbitrary TeX commands can be used if they're
 % surrounded by @ signs.
+\def\codeblockbeginpenalty{0}  % default penalty before codeblock
 \newcommand{\CodeBlockSetup}{%
 \lstset{escapechar=@, aboveskip=\parskip, belowskip=0pt,
-        midpenalty=500, endpenalty=-50,
+        beginpenalty=\codeblockbeginpenalty, midpenalty=500, endpenalty=-50,
         emptylinepenalty=-250, semicolonpenalty=0}%
 \renewcommand{\tcode}[1]{\textup{\CodeStylex{##1}}}
 \renewcommand{\term}[1]{\textit{##1}}%
@@ -473,8 +474,27 @@
 
 \lstnewenvironment{codeblock}{\CodeBlockSetup}{}
 
-% Left-align listings titles
 \makeatletter
+
+\newsavebox\@signalbox
+
+% Redefine \begin{codeblock} to look for an immediately-preceding
+% \begin{example}.
+\global\@namedef{codeblock}{%
+  \def\lstenv@name {codeblock}\begingroup%
+  \ifhmode%                             no last box in vertical mode
+    \setbox\@signalbox=\lastbox%        grab and consume last box
+    \copy\@signalbox%                   typeset the last box again
+    \ifhbox\@signalbox%
+      \ifdim\wd\@signalbox=0pt%         zero-width box is our marker
+        \def\codeblockbeginpenalty{100}%
+      \fi%
+    \fi%
+  \fi%
+  \lst@setcatcodes \catcode \active=\active \csname codeblock@\endcsname%
+}
+
+% Left-align listings titles
 \def\lst@maketitle{\@makeleftcaption\lst@title@dropdelim}
 \long\def\@makeleftcaption#1#2{%
   \vskip\abovecaptionskip