@value{UPDATED}), the @acronym{GNU} parser generator.
Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998,
-1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
+1999, 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc.
@quotation
Permission is granted to copy, distribute and/or modify this document
* Union Decl:: Declaring the set of all semantic value types.
* Type Decl:: Declaring the choice of type for a nonterminal symbol.
* Destructor Decl:: Declaring how symbols are freed.
-* Expect Decl:: Suppressing warnings about shift/reduce conflicts.
+* Expect Decl:: Suppressing warnings about parsing conflicts.
* Start Decl:: Specifying the start symbol.
* Pure Decl:: Requesting a reentrant parser.
* Decl Summary:: Table of all Bison declarations.
%@}
%union @{
- long n;
+ long int n;
tree t; /* @r{@code{tree} is defined in @file{ptypes.h}.} */
@}
In most programs, you will need different data types for different kinds
of tokens and groupings. For example, a numeric constant may need type
-@code{int} or @code{long}, while a string constant needs type @code{char *},
+@code{int} or @code{long int}, while a string constant needs type @code{char *},
and an identifier might need a pointer to an entry in the symbol table.
To use more than one data type for semantic values in one parser, Bison
* Union Decl:: Declaring the set of all semantic value types.
* Type Decl:: Declaring the choice of type for a nonterminal symbol.
* Destructor Decl:: Declaring how symbols are freed.
-* Expect Decl:: Suppressing warnings about shift/reduce conflicts.
+* Expect Decl:: Suppressing warnings about parsing conflicts.
* Start Decl:: Specifying the start symbol.
* Pure Decl:: Requesting a reentrant parser.
* Decl Summary:: Table of all Bison declarations.
Precedence}.
You can explicitly specify the numeric code for a token type by appending
-an integer value in the field immediately following the token name:
+a decimal or hexadecimal integer value in the field immediately
+following the token name:
@example
%token NUM 300
+%token XNUM 0x12d // a GNU extension
@end example
@noindent
@cindex warnings, preventing
@cindex conflicts, suppressing warnings of
@findex %expect
+@findex %expect-rr
Bison normally warns if there are any conflicts in the grammar
(@pxref{Shift/Reduce, ,Shift/Reduce Conflicts}), but most real grammars
given if there are either more or fewer conflicts, or if there are any
reduce/reduce conflicts.
+For normal LALR(1) parsers, reduce/reduce conflicts are more serious,
+and should be eliminated entirely. Bison will always report
+reduce/reduce conflicts for these parsers. With GLR parsers, however,
+both shift/reduce and reduce/reduce are routine (otherwise, there
+would be no need to use GLR parsing). Therefore, it is also possible
+to specify an expected number of reduce/reduce conflicts in GLR
+parsers, using the declaration:
+
+@example
+%expect-rr @var{n}
+@end example
+
In general, using @code{%expect} involves these steps:
@itemize @bullet
@example
#! /bin/sh
-bison -y "$@"
+bison -y "$@@"
@end example
@end table
functions like @samp{yy_switch_to_buffer} that manipulate multiple
input buffers.
+If your Flex-generated scanner uses start conditions (@pxref{Start
+conditions, , Start conditions, flex, The Flex Manual}), you might
+also want to reset the scanner's state, i.e., go back to the initial
+start condition, through a call to @samp{BEGIN (0)}.
+
@node Strings are Destroyed
@section Strings are Destroyed