Extract calc++ from the documentation.

* doc/bison.texinfo (Calc++): Add the extraction marks.
* examples/extexi: New, from the aborted GNU Programming 2E.
Separate the different paragraph of a file with empty lines.
* examples/Makefile: Use it to extract the whole calc++ example.

examples/calc++/calc++-parser.yy

@@ -1,48 +1,44 @@
-%skeleton "lalr1.cc"                                  /*  -*- C++ -*- */
+#line 7188 "../../doc/bison.texinfo"
+%skeleton "lalr1.cc"                          /*  -*- C++ -*- */
 %define "parser_class_name" "calcxx_parser"
 %defines
 %{
 # include <string>
 # include "calc++-driver.hh"
 %}
-
-%error-verbose
-
+#line 7204 "../../doc/bison.texinfo"
 // The parsing context.
 %parse-param { calcxx_driver& driver }
 %lex-param   { calcxx_driver& driver }
-
+#line 7217 "../../doc/bison.texinfo"
 %locations
 %initial-action
 {
   // Initialize the initial location.
   @$.begin.filename = @$.end.filename = &driver.file;
 };
-
-// Define yydebug.
+#line 7231 "../../doc/bison.texinfo"
 %debug
-
+%error-verbose
+#line 7241 "../../doc/bison.texinfo"
 // Symbols.
-
 %union
 {
-  /// Value of a numeric literal.
   int          ival;
-  /// Name of a variable.
   std::string *sval;
 };
-
+#line 7258 "../../doc/bison.texinfo"
 %token        YYEOF          0 "end of file"
 %token        TOKEN_ASSIGN     ":="
 %token <sval> TOKEN_IDENTIFIER "identifier"
 %token <ival> TOKEN_NUMBER     "number"
 %type  <ival> exp              "expression"
-
+#line 7271 "../../doc/bison.texinfo"
 %printer    { debug_stream () << *$$; } "identifier"
 %destructor { delete $$; } "identifier"
 
 %printer    { debug_stream () << $$; } "number" "expression"
-
+#line 7282 "../../doc/bison.texinfo"
 %%
 %start unit;
 unit: assignments exp  { driver.result = $2; };
@@ -61,8 +57,10 @@ exp: exp '+' exp   { $$ = $1 + $3; }
    | TOKEN_IDENTIFIER  { $$ = driver.variables[*$1]; }
    | TOKEN_NUMBER      { $$ = $1; };
 %%
+#line 7308 "../../doc/bison.texinfo"
 void
-yy::calcxx_parser::error (const location& l, const std::string& m)
+yy::calcxx_parser::error (const yy::calcxx_parser::location_type& l,
+                          const std::string& m)
 {
   driver.error (l, m);
 }