I installed this.
2006-01-11 Joel E. Denny <[EMAIL PROTECTED]>
* doc/bison.texinfo: Fix some typos.
(GLR Semantic Actions): New subsection discussing special
considerations because GLR semantic actions might be deferred.
(Actions): Mention look-ahead usage of yylval.
(Actions and Locations): Mention look-ahead usage of yylloc.
(Special Features for Use in Actions): Add YYEOF entry and mention it
in the yychar entry.
In the yychar entry, remove mention of the local yychar case (pure
parser) since this is irrelevant information when writing semantic
actions and since it's already discussed in `Bison Symbols' where
yychar is otherwise described as an external variable.
In the yychar entry, don't call it the `current' look-ahead since it
isn't when semantic actions are deferred.
In the yychar and yyclearin entries, add note about deferred semantic
actions.
Add yylloc and yylval entries discussing look-ahead usage.
(Look-Ahead Tokens): When discussing yychar, don't call it the
`current' look-ahead, and do mention yylval and yylloc.
(Error Recovery): Cross-reference `Action Features' when mentioning
yyclearin.
(Bison Symbols): In the yychar entry, don't call it the `current'
look-ahead.
In the yylloc and yylval entries, mention look-ahead usage.
Index: doc/bison.texinfo
===================================================================
RCS file: /sources/bison/bison/doc/bison.texinfo,v
retrieving revision 1.171
diff -p -u -r1.171 bison.texinfo
--- doc/bison.texinfo 3 Jan 2006 22:35:45 -0000 1.171
+++ doc/bison.texinfo 11 Jan 2006 22:38:03 -0000
@@ -44,7 +44,7 @@ This manual is for @acronym{GNU} Bison (
@value{UPDATED}), the @acronym{GNU} parser generator.
Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998,
-1999, 2000, 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc.
+1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc.
@quotation
Permission is granted to copy, distribute and/or modify this document
@@ -145,9 +145,10 @@ The Concepts of Bison
Writing @acronym{GLR} Parsers
-* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous
grammars
-* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities
-* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler
+* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous
grammars.
+* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities.
+* GLR Semantic Actions:: Deferred semantic actions have special concerns.
+* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler.
Examples
@@ -733,9 +734,10 @@ user-defined function on the resulting v
merged result.
@menu
-* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous
grammars
-* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities
-* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler
+* Simple GLR Parsers:: Using @acronym{GLR} parsers on unambiguous
grammars.
+* Merging GLR Parses:: Using @acronym{GLR} parsers to resolve ambiguities.
+* GLR Semantic Actions:: Deferred semantic actions have special concerns.
+* Compiler Requirements:: @acronym{GLR} parsers require a modern C compiler.
@end menu
@node Simple GLR Parsers
@@ -1094,6 +1096,52 @@ productions that participate in any part
and the parser will report an error during any parse that results in
the offending merge.
[EMAIL PROTECTED] GLR Semantic Actions
[EMAIL PROTECTED] GLR Semantic Actions
+
[EMAIL PROTECTED] deferred semantic actions
+By definition, a deferred semantic action is not performed at the same time as
+the associated reduction.
+This raises caveats for several Bison features you might use in a semantic
+action in a @acronym{GLR} parser.
+
[EMAIL PROTECTED] yychar
[EMAIL PROTECTED] @acronym{GLR} parsers and @code{yychar}
[EMAIL PROTECTED] yylval
[EMAIL PROTECTED] @acronym{GLR} parsers and @code{yylval}
[EMAIL PROTECTED] yylloc
[EMAIL PROTECTED] @acronym{GLR} parsers and @code{yylloc}
+In any semantic action, you can examine @code{yychar} to determine the type of
+the look-ahead token present at the time of the associated reduction.
+After checking that @code{yychar} is not set to @code{YYEMPTY} or @code{YYEOF},
+you can then examine @code{yylval} and @code{yylloc} to determine the
+look-ahead token's semantic value and location, if any.
+In a nondeferred semantic action, you can also modify any of these variables to
+influence syntax analysis.
[EMAIL PROTECTED], ,Look-Ahead Tokens}.
+
[EMAIL PROTECTED] yyclearin
[EMAIL PROTECTED] @acronym{GLR} parsers and @code{yyclearin}
+In a deferred semantic action, it's too late to influence syntax analysis.
+In this case, @code{yychar}, @code{yylval}, and @code{yylloc} are set to
+shallow copies of the values they had at the time of the associated reduction.
+For this reason alone, modifying them is dangerous.
+Moreover, the result of modifying them is undefined and subject to change with
+future versions of Bison.
+For example, if a semantic action might be deferred, you should never write it
+to invoke @code{yyclearin} (@pxref{Action Features}) or to attempt to free
+memory referenced by @code{yylval}.
+
[EMAIL PROTECTED] YYERROR
[EMAIL PROTECTED] @acronym{GLR} parsers and @code{YYERROR}
+Another Bison feature requiring special consideration is @code{YYERROR}
+(@pxref{Action Features}), which you can invoke in any semantic action to
+initiate error recovery.
+During deterministic @acronym{GLR} operation, the effect of @code{YYERROR} is
+the same as its effect in an @acronym{LALR}(1) parser.
+In a deferred semantic action, its effect is undefined.
[EMAIL PROTECTED] The effect is probably a syntax error at the split point.
+
@node Compiler Requirements
@subsection Considerations when Compiling @acronym{GLR} Parsers
@cindex @code{inline}
@@ -3140,6 +3188,12 @@ As long as @code{bar} is used only in th
always refers to the @code{expr} which precedes @code{bar} in the
definition of @code{foo}.
[EMAIL PROTECTED] yylval
+It is also possible to access the semantic value of the look-ahead token, if
+any, from a semantic action.
+This semantic value is stored in @code{yylval}.
[EMAIL PROTECTED] Features, ,Special Features for Use in Actions}.
+
@node Action Types
@subsection Data Types of Values in Actions
@cindex action data types
@@ -3457,6 +3511,12 @@ exp: @dots{}
@end group
@end example
[EMAIL PROTECTED] yylloc
+It is also possible to access the location of the look-ahead token, if any,
+from a semantic action.
+This location is stored in @code{yylloc}.
[EMAIL PROTECTED] Features, ,Special Features for Use in Actions}.
+
@node Location Default Action
@subsection Default Action for Locations
@vindex YYLLOC_DEFAULT
@@ -4763,6 +4823,12 @@ In either case, the rest of the action i
Value stored in @code{yychar} when there is no look-ahead token.
@end deffn
[EMAIL PROTECTED] {Macro} YYEOF
[EMAIL PROTECTED] YYEOF
+Value stored in @code{yychar} when the look-ahead is the end of the input
+stream.
[EMAIL PROTECTED] deffn
+
@deffn {Macro} YYERROR;
@findex YYERROR
Cause an immediate syntax error. This statement initiates error
@@ -4779,15 +4845,20 @@ is recovering from a syntax error, and 0
@end deffn
@deffn {Variable} yychar
-Variable containing the current look-ahead token. (In a pure parser,
-this is actually a local variable within @code{yyparse}.) When there is
-no look-ahead token, the value @code{YYEMPTY} is stored in the variable.
+Variable containing either the look-ahead token, or @code{YYEOF} when the
+look-ahead is the end of the input stream, or @code{YYEMPTY} when no look-ahead
+has been performed so the next token is not yet known.
+Do not modify @code{yychar} in a deferred semantic action (@pxref{GLR Semantic
+Actions}).
@xref{Look-Ahead, ,Look-Ahead Tokens}.
@end deffn
@deffn {Macro} yyclearin;
Discard the current look-ahead token. This is useful primarily in
-error rules. @xref{Error Recovery}.
+error rules.
+Do not invoke @code{yyclearin} in a deferred semantic action (@pxref{GLR
+Semantic Actions}).
[EMAIL PROTECTED] Recovery}.
@end deffn
@deffn {Macro} yyerrok;
@@ -4796,6 +4867,22 @@ errors. This is useful primarily in err
@xref{Error Recovery}.
@end deffn
[EMAIL PROTECTED] {Variable} yylloc
+Variable containing the look-ahead token location when @code{yychar} is not set
+to @code{YYEMPTY} or @code{YYEOF}.
+Do not modify @code{yylloc} in a deferred semantic action (@pxref{GLR Semantic
+Actions}).
[EMAIL PROTECTED] and Locations, ,Actions and Locations}.
[EMAIL PROTECTED] deffn
+
[EMAIL PROTECTED] {Variable} yylval
+Variable containing the look-ahead token semantic value when @code{yychar} is
+not set to @code{YYEMPTY} or @code{YYEOF}.
+Do not modify @code{yylval} in a deferred semantic action (@pxref{GLR Semantic
+Actions}).
[EMAIL PROTECTED], ,Actions}.
[EMAIL PROTECTED] deffn
+
@deffn {Value} @@$
@findex @@$
Acts like a structure variable containing information on the textual location
@@ -5033,7 +5120,11 @@ doing so would produce on the stack the
'!'}. No rule allows that sequence.
@vindex yychar
-The current look-ahead token is stored in the variable @code{yychar}.
[EMAIL PROTECTED] yylval
[EMAIL PROTECTED] yylloc
+The look-ahead token is stored in the variable @code{yychar}.
+Its semantic value and location, if any, are stored in the variables
[EMAIL PROTECTED] and @code{yylloc}.
@xref{Action Features, ,Special Features for Use in Actions}.
@node Shift/Reduce
@@ -5850,6 +5941,7 @@ The previous look-ahead token is reanaly
this is unacceptable, then the macro @code{yyclearin} may be used to clear
this token. Write the statement @samp{yyclearin;} in the error rule's
action.
[EMAIL PROTECTED] Features, ,Special Features for Use in Actions}.
For example, suppose that on a syntax error, an error handling routine is
called that advances the input stream to some point where parsing should
@@ -8039,7 +8131,7 @@ token. @xref{Action Features, ,Special
@end deffn
@deffn {Variable} yychar
-External integer variable that contains the integer value of the current
+External integer variable that contains the integer value of the
look-ahead token. (In a pure parser, it is a local variable within
@code{yyparse}.) Error-recovery rule actions may examine this variable.
@xref{Action Features, ,Special Features for Use in Actions}.
@@ -8100,7 +8192,7 @@ the next token. @xref{Lexical, ,The Lex
@deffn {Macro} YYLEX_PARAM
An obsolete macro for specifying an extra argument (or list of extra
-arguments) for @code{yyparse} to pass to @code{yylex}. he use of this
+arguments) for @code{yyparse} to pass to @code{yylex}. The use of this
macro is deprecated, and is supported only for Yacc like parsers.
@xref{Pure Calling,, Calling Conventions for Pure Parsers}.
@end deffn
@@ -8109,9 +8201,12 @@ macro is deprecated, and is supported on
External variable in which @code{yylex} should place the line and column
numbers associated with a token. (In a pure parser, it is a local
variable within @code{yyparse}, and its address is passed to
[EMAIL PROTECTED]) You can ignore this variable if you don't use the
[EMAIL PROTECTED]@@} feature in the grammar actions. @xref{Token Locations,
-,Textual Locations of Tokens}.
[EMAIL PROTECTED])
+You can ignore this variable if you don't use the @samp{@@} feature in the
+grammar actions.
[EMAIL PROTECTED] Locations, ,Textual Locations of Tokens}.
+In semantic actions, it stores the location of the look-ahead token.
[EMAIL PROTECTED] and Locations, ,Actions and Locations}.
@end deffn
@deffn {Type} YYLTYPE
@@ -8123,7 +8218,10 @@ members. @xref{Location Type, , Data Ty
External variable in which @code{yylex} should place the semantic
value associated with a token. (In a pure parser, it is a local
variable within @code{yyparse}, and its address is passed to
[EMAIL PROTECTED]) @xref{Token Values, ,Semantic Values of Tokens}.
[EMAIL PROTECTED])
[EMAIL PROTECTED] Values, ,Semantic Values of Tokens}.
+In semantic actions, it stores the semantic value of the look-ahead token.
[EMAIL PROTECTED], ,Actions}.
@end deffn
@deffn {Macro} YYMAXDEPTH
@@ -8384,7 +8482,7 @@ grammatically indivisible. The piece of
@c LocalWords: yychar yydebug msg YYNTOKENS YYNNTS YYNRULES YYNSTATES
@c LocalWords: cparse clex deftypefun NE defmac YYACCEPT YYABORT param
@c LocalWords: strncmp intval tindex lvalp locp llocp typealt YYBACKUP
[EMAIL PROTECTED] LocalWords: YYEMPTY YYRECOVERING yyclearin GE def UMINUS
maybeword
[EMAIL PROTECTED] LocalWords: YYEMPTY YYEOF YYRECOVERING yyclearin GE def
UMINUS maybeword
@c LocalWords: Johnstone Shamsa Sadaf Hussain Tomita TR uref YYMAXDEPTH
@c LocalWords: YYINITDEPTH stmnts ref stmnt initdcl maybeasm VCG notype
@c LocalWords: hexflag STR exdent itemset asis DYYDEBUG YYFPRINTF args
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