More.

[bison.git] / doc / bison.texinfo

diff --git a/doc/bison.texinfo b/doc/bison.texinfo
index 7c0b3454e1c99b1016d964a729611a226cd96da4..d26295c64c162b5c1b74ad7cf11106a7dfe85564 100644 (file)
--- a/doc/bison.texinfo
+++ b/doc/bison.texinfo
@@ -47,7 +47,7 @@ END-INFO-DIR-ENTRY
 This file documents the Bison parser generator.
 
 Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998, 1999,
-2000, 2001
+2000, 2001, 2002
 Free Software Foundation, Inc.
 
 Permission is granted to make and distribute verbatim copies of
@@ -89,7 +89,7 @@ instead of in the original English.
 @page
 @vskip 0pt plus 1filll
 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998,
-1999, 2000, 2001
+1999, 2000, 2001, 2002
 Free Software Foundation, Inc.
 
 @sp 2
@@ -1083,7 +1083,7 @@ The return value of the lexical analyzer function is a numeric code which
 represents a token type.  The same text used in Bison rules to stand for
 this token type is also a C expression for the numeric code for the type.
 This works in two ways.  If the token type is a character literal, then its
-numeric code is the ASCII code for that character; you can use the same
+numeric code is that of the character; you can use the same
 character literal in the lexical analyzer to express the number.  If the
 token type is an identifier, that identifier is defined by Bison as a C
 macro whose definition is the appropriate number.  In this example,
@@ -1104,8 +1104,8 @@ Here is the code for the lexical analyzer:
 @example
 @group
 /* Lexical analyzer returns a double floating point
-   number on the stack and the token NUM, or the ASCII
-   character read if not a number.  Skips all blanks
+   number on the stack and the token NUM, or the numeric code
+   of the character read if not a number.  Skips all blanks
    and tabs, returns 0 for EOF. */
 
 #include <ctype.h>
@@ -2148,7 +2148,7 @@ your program will confuse other readers.
 
 All the usual escape sequences used in character literals in C can be
 used in Bison as well, but you must not use the null character as a
-character literal because its ASCII code, zero, is the code @code{yylex}
+character literal because its numeric code, zero, is the code @code{yylex}
 returns for end-of-input (@pxref{Calling Convention, ,Calling Convention
 for @code{yylex}}).
 
@@ -2189,7 +2189,7 @@ on when the parser function returns that symbol.
 The value returned by @code{yylex} is always one of the terminal symbols
 (or 0 for end-of-input).  Whichever way you write the token type in the
 grammar rules, you write it the same way in the definition of @code{yylex}.
-The numeric code for a character token type is simply the ASCII code for
+The numeric code for a character token type is simply the numeric code of
 the character, so @code{yylex} can use the identical character constant to
 generate the requisite code.  Each named token type becomes a C macro in
 the parser file, so @code{yylex} can use the name to stand for the code.
@@ -2202,9 +2202,27 @@ option when you run Bison, so that it will write these macro definitions
 into a separate header file @file{@var{name}.tab.h} which you can include
 in the other source files that need it.  @xref{Invocation, ,Invoking Bison}.
 
+The @code{yylex} function must use the same character set and encoding
+that was used by Bison.  For example, if you run Bison in an
+@sc{ascii} environment, but then compile and run the resulting program
+in an environment that uses an incompatible character set like
+@sc{ebcdic}, the resulting program will probably not work because the
+tables generated by Bison will assume @sc{ascii} numeric values for
+character tokens.  Portable grammars should avoid non-@sc{ascii}
+character tokens, as implementations in practice often use different
+and incompatible extensions in this area.  However, it is standard
+practice for software distributions to contain C source files that
+were generated by Bison in an @sc{ascii} environment, so installers on
+platforms that are incompatible with @sc{ascii} must rebuild those
+files before compiling them.
+
 The symbol @code{error} is a terminal symbol reserved for error recovery
 (@pxref{Error Recovery}); you shouldn't use it for any other purpose.
 In particular, @code{yylex} should never return this value.
+The default value of the error token is 256, so in the
+unlikely event that you need to use a character token with numeric
+value 256 you must reassign the error token's value with a
+@code{%token} declaration.
 
 @node Rules
 @section Syntax of Grammar Rules
@@ -2942,7 +2960,7 @@ an integer value in the field immediately following the token name:
 @noindent
 It is generally best, however, to let Bison choose the numeric codes for
 all token types.  Bison will automatically select codes that don't conflict
-with each other or with ASCII characters.
+with each other or with normal characters.
 
 In the event that the stack type is a union, you must augment the
 @code{%token} or other token declaration to include the data type