doc: token.prefix

* doc/bison.simple (Decl Summary): Document token.prefix.
	(Calc++ Parser): Various fixes.
	Formatting changes.
	Use token.prefix.
	Introduce a macro TOKEN to shorten the code and make it more
	readable.
	(Calc++ Scanner): Adjust.
	* NEWS (Variable token.prefix): New.

doc/bison.texinfo

@@ -5190,10 +5190,47 @@ is not already defined, so that the debugging facilities are compiled.
 
 @item Default Value: @code{false}
 @end itemize
-@end table
 @c parse.trace
+
+@item token.prefix
+@findex %define token.prefix
+
+@itemize
+@item Languages(s): all
+
+@item Purpose:
+Add a prefix to the token names when generating their definition in the
+target language.  For instance
+
+@example
+%token FILE for ERROR
+%define token.prefix "TOK_"
+%%
+start: FILE for ERROR;
+@end example
+
+@noindent
+generates the definition of the symbols @code{TOK_FILE}, @code{TOK_for},
+and @code{TOK_ERROR} in the generated source files.  In particular, the
+scanner must use these prefixed token names, while the grammar itself
+may still use the short names (as in the sample rule given above).  The
+generated informational files (@file{*.output}, @file{*.xml},
+@file{*.dot}) are not modified by this prefix.  See @ref{Calc++ Parser}
+and @ref{Calc++ Scanner}, for a complete example.
+
+@item Accepted Values:
+Any string.  Should be a valid identifier prefix in the target language,
+in other words, it should typically be an identifier itself (sequence of
+letters, underscores, and ---not at the beginning--- digits).
+
+@item Default Value:
+empty
+@end itemize
+@c token.prefix
+
+@end table
 @end deffn
-@c %define
+@c ----------------------------------------------------------   %define
 
 @deffn {Directive} %defines
 Write a header file containing macro definitions for the token type
@@ -8777,13 +8814,14 @@ The code between @samp{%code @{} and @samp{@}} is output in the
 
 @noindent
 The token numbered as 0 corresponds to end of file; the following line
-allows for nicer error messages referring to ``end of file'' instead
-of ``$end''.  Similarly user friendly named are provided for each
-symbol.  Note that the tokens names are prefixed by @code{TOKEN_} to
-avoid name clashes.
+allows for nicer error messages referring to ``end of file'' instead of
+``$end''.  Similarly user friendly names are provided for each symbol.
+To avoid name clashes in the generated files (@pxref{Calc++ Scanner}),
+prefix tokens with @code{TOK_} (@pxref{Decl Summary,, token.prefix}).
 
 @comment file: calc++-parser.yy
 @example
+%define token.prefix "TOK_"
 %token        END      0 "end of file"
 %token        ASSIGN     ":="
 %token <sval> IDENTIFIER "identifier"
@@ -8813,22 +8851,24 @@ The grammar itself is straightforward.
 %start unit;
 unit: assignments exp  @{ driver.result = $2; @};
 
-assignments: assignments assignment @{@}
-           | /* Nothing.  */        @{@};
+assignments:
+  assignments assignment @{@}
+| /* Nothing.  */        @{@};
 
 assignment:
-     "identifier" ":=" exp
+  "identifier" ":=" exp
        @{ driver.variables[*$1] = $3; delete $1; @};
 
 %left '+' '-';
 %left '*' '/';
-exp: exp '+' exp   @{ $$ = $1 + $3; @}
-   | exp '-' exp   @{ $$ = $1 - $3; @}
-   | exp '*' exp   @{ $$ = $1 * $3; @}
-   | exp '/' exp   @{ $$ = $1 / $3; @}
-   | '(' exp ')'   @{ $$ = $2; @}
-   | "identifier"  @{ $$ = driver.variables[*$1]; delete $1; @}
-   | "number"      @{ $$ = $1; @};
+exp:
+  exp '+' exp   @{ $$ = $1 + $3; @}
+| exp '-' exp   @{ $$ = $1 - $3; @}
+| exp '*' exp   @{ $$ = $1 * $3; @}
+| exp '/' exp   @{ $$ = $1 / $3; @}
+| '(' exp ')'   @{ $$ = $2; @}
+| "identifier"  @{ $$ = driver.variables[*$1]; delete $1; @}
+| "number"      @{ $$ = $1; @};
 %%
 @end example
 
@@ -8869,10 +8909,10 @@ parser's to get the set of defined tokens.
 # undef yywrap
 # define yywrap() 1
 
-/* By default yylex returns int, we use token_type.
-   Unfortunately yyterminate by default returns 0, which is
+/* By default yylex returns an int; we use token_type.
+   The default yyterminate implementation returns 0, which is
    not of token_type.  */
-#define yyterminate() return token::END
+#define yyterminate() return TOKEN(END)
 %@}
 @end example
 
@@ -8920,28 +8960,32 @@ preceding tokens.  Comments would be treated equally.
 @end example
 
 @noindent
-The rules are simple, just note the use of the driver to report errors.
-It is convenient to use a typedef to shorten
-@code{yy::calcxx_parser::token::identifier} into
-@code{token::identifier} for instance.
+The rules are simple.  The driver is used to report errors.  It is
+convenient to use a macro to shorten
+@code{yy::calcxx_parser::token::TOK_@var{Name}} into
+@code{TOKEN(@var{Name})}; note the token prefix, @code{TOK_}.
 
 @comment file: calc++-scanner.ll
 @example
 %@{
-  typedef yy::calcxx_parser::token token;
+# define TOKEN(Name)                          \
+  yy::calcxx_parser::token::TOK_ ## Name
 %@}
            /* Convert ints to the actual type of tokens.  */
 [-+*/()]   return yy::calcxx_parser::token_type (yytext[0]);
-":="       return token::ASSIGN;
+":="       return TOKEN(ASSIGN);
 @{int@}      @{
   errno = 0;
   long n = strtol (yytext, NULL, 10);
   if (! (INT_MIN <= n && n <= INT_MAX && errno != ERANGE))
     driver.error (*yylloc, "integer is out of range");
   yylval->ival = n;
-  return token::NUMBER;
+  return TOKEN(NUMBER);
+@}
+@{id@}       @{
+  yylval->sval = new std::string (yytext);
+  return TOKEN(IDENTIFIER);
 @}
-@{id@}       yylval->sval = new std::string (yytext); return token::IDENTIFIER;
 .          driver.error (*yylloc, "invalid character");
 %%
 @end example