Start a set of simple examples.

* examples/calc++/Makefile, examples/calc++/calc++-driver.cc,
* examples/calc++/calc++-driver.hh,
* examples/calc++/calc++-parser.yy,
* examples/calc++/calc++-scanner.ll, examples/calc++/calc++.cc,
* examples/calc++/compile, examples/calc++/test: New.

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

@@ -0,0 +1,68 @@
+%skeleton "lalr1.cc"                                  /*  -*- C++ -*- */
+%define "parser_class_name" "calcxx_parser"
+%defines
+%{
+# include <string>
+# include "calc++-driver.hh"
+%}
+
+%error-verbose
+
+// The parsing context.
+%parse-param { calcxx_driver& driver }
+%lex-param   { calcxx_driver& driver }
+
+%locations
+%initial-action
+{
+  // Initialize the initial location.
+  @$.begin.filename = @$.end.filename = &driver.file;
+};
+
+// Define yydebug.
+%debug
+
+// Symbols.
+
+%union
+{
+  /// Value of a numeric literal.
+  int          ival;
+  /// Name of a variable.
+  std::string *sval;
+};
+
+%token        YYEOF          0 "end of file"
+%token        TOKEN_ASSIGN     ":="
+%token <sval> TOKEN_IDENTIFIER "identifier"
+%token <ival> TOKEN_NUMBER     "number"
+%type  <ival> exp              "expression"
+
+%printer    { debug_stream () << *$$; } "identifier"
+%destructor { delete $$; } "identifier"
+
+%printer    { debug_stream () << $$; } "number" "expression"
+
+%%
+%start unit;
+unit: assignments exp  { driver.result = $2; };
+
+assignments: assignments assignment {}
+           | /* Nothing. */         {};
+
+assignment: TOKEN_IDENTIFIER ":=" exp { driver.variables[*$1] = $3; };
+
+%left '+' '-';
+%left '*' '/';
+exp: exp '+' exp   { $$ = $1 + $3; }
+   | exp '-' exp   { $$ = $1 - $3; }
+   | exp '*' exp   { $$ = $1 * $3; }
+   | exp '/' exp   { $$ = $1 / $3; }
+   | TOKEN_IDENTIFIER  { $$ = driver.variables[*$1]; }
+   | TOKEN_NUMBER      { $$ = $1; };
+%%
+void
+yy::calcxx_parser::error (const location& l, const std::string& m)
+{
+  driver.error (l, m);
+}