src/Pure/Tools/doc.scala

   private def examples(): List[Entry] =
     Section("Examples", true) ::
       Path.split(Isabelle_System.getenv_strict("ISABELLE_DOCS_EXAMPLES")).map(file =>
         text_file(file) match {
           case Some(entry) => entry
-          case None => error("Bad ISABELLE_DOCS_EXAMPLES entry: " + file)
+          case None => error("Bad entry in ISABELLE_DOCS_EXAMPLES: " + file)
         })
 
   def contents(): List[Entry] =
     (for {
       (dir, line) <- contents_lines()

   /* command line entry point */
 
   def main(args: Array[String])
   {
     Command_Line.tool {
+      val entries = contents()
       if (args.isEmpty) Console.println(cat_lines(contents_lines().map(_._2)))
       else {
-        val entries = contents()
         args.foreach(arg =>
           entries.collectFirst { case Doc(name, _, path) if arg == name => path } match {
             case Some(path) => view(path)
             case None => error("No Isabelle documentation entry: " + quote(arg))
           }