a -> an (minor typo fix)

[bison.git] / doc / bison.texinfo

diff --git a/doc/bison.texinfo b/doc/bison.texinfo
index 26d03040eeaad82898efc57116db6a395e86d7bf..8f35ac602d8ae860b86d80bb04c36351f6dee506 100644 (file)
--- a/doc/bison.texinfo
+++ b/doc/bison.texinfo
@@ -16,6 +16,10 @@
 @c @clear shorttitlepage-enabled
 @c @set shorttitlepage-enabled
 
 @c @clear shorttitlepage-enabled
 @c @set shorttitlepage-enabled
 

+@c Set following if you want to document %default-prec and %no-default-prec.
+@c This feature is experimental and may change in future Bison versions.
+@c @set defaultprec
+

 @c ISPELL CHECK: done, 14 Jan 1993 --bob
 
 @c Check COPYRIGHT dates.  should be updated in the titlepage, ifinfo
 @c ISPELL CHECK: done, 14 Jan 1993 --bob
 
 @c Check COPYRIGHT dates.  should be updated in the titlepage, ifinfo


@@ -39,7 +43,7 @@
 This manual is for @acronym{GNU} Bison (version @value{VERSION},
 @value{UPDATED}), the @acronym{GNU} parser generator.
 
 This manual is for @acronym{GNU} Bison (version @value{VERSION},
 @value{UPDATED}), the @acronym{GNU} parser generator.
 

-Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998, 2003,
+Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998,

 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
 
 @quotation
 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
 
 @quotation


@@ -284,8 +288,10 @@ Invoking Bison
 Frequently Asked Questions
 
 * Parser Stack Overflow::      Breaking the Stack Limits
 Frequently Asked Questions
 
 * Parser Stack Overflow::      Breaking the Stack Limits

-* How Can I Reset @code{yyparse}::    @code{yyparse} Keeps some State
+* How Can I Reset the Parser:: @code{yyparse} Keeps some State

 * Strings are Destroyed::      @code{yylval} Loses Track of Strings
 * Strings are Destroyed::      @code{yylval} Loses Track of Strings

+* C++ Parsers::                Compiling Parsers with C++ Compilers
+* Implementing Loops::         Control Flow in the Calculator

 
 Copying This Manual
 
 
 Copying This Manual
 


@@ -350,7 +356,7 @@ encourage people to make other software free.  So we decided to make the
 practical conditions for using Bison match the practical conditions for
 using the other @acronym{GNU} tools.
 
 practical conditions for using Bison match the practical conditions for
 using the other @acronym{GNU} tools.
 

-This exception applies only when Bison is generating C code for a
+This exception applies only when Bison is generating C code for an

 @acronym{LALR}(1) parser; otherwise, the @acronym{GPL} terms operate
 as usual.  You can
 tell whether the exception applies to your @samp{.c} output file by
 @acronym{LALR}(1) parser; otherwise, the @acronym{GPL} terms operate
 as usual.  You can
 tell whether the exception applies to your @samp{.c} output file by


@@ -1413,7 +1419,7 @@ here is the definition we will use:
 void
 yyerror (char const *s)
 @{
 void
 yyerror (char const *s)
 @{

-  printf ("%s\n", s);
+  fprintf (stderr, "%s\n", s);

 @}
 @end group
 @end example
 @}
 @end group
 @end example


@@ -2475,7 +2481,8 @@ does not enforce this convention, but if you depart from it, people who
 read your program will be confused.
 
 All the escape sequences used in string literals in C can be used in
 read your program will be confused.
 
 All the escape sequences used in string literals in C can be used in

-Bison as well.  However, unlike Standard C, trigraphs have no special
+Bison as well, except that you must not use a null character within a
+string literal.  Also, unlike Standard C, trigraphs have no special

 meaning in Bison string literals, nor is backslash-newline allowed.  A
 literal string token must contain two or more characters; for a token
 containing just one character, use a character token (see above).
 meaning in Bison string literals, nor is backslash-newline allowed.  A
 literal string token must contain two or more characters; for a token
 containing just one character, use a character token (see above).


@@ -2795,9 +2802,10 @@ Actions, ,Actions in Mid-Rule}).
 The C code in an action can refer to the semantic values of the components
 matched by the rule with the construct @code{$@var{n}}, which stands for
 the value of the @var{n}th component.  The semantic value for the grouping
 The C code in an action can refer to the semantic values of the components
 matched by the rule with the construct @code{$@var{n}}, which stands for
 the value of the @var{n}th component.  The semantic value for the grouping

-being constructed is @code{$$}.  (Bison translates both of these constructs
-into array element references when it copies the actions into the parser
-file.)
+being constructed is @code{$$}.  Bison translates both of these
+constructs into expressions of the appropriate type when it copies the
+actions into the parser file.  @code{$$} is translated to a modifiable
+lvalue, so it can be assigned to.

 
 Here is a typical example:
 
 
 Here is a typical example:
 


@@ -3080,8 +3088,6 @@ Though grammar rules and semantic actions are enough to write a fully
 functional parser, it can be useful to process some additional information,
 especially symbol locations.
 
 functional parser, it can be useful to process some additional information,
 especially symbol locations.
 

-@c (terminal or not) ?
-

 The way locations are handled is defined by providing a data type, and
 actions to take when rules are matched.
 
 The way locations are handled is defined by providing a data type, and
 actions to take when rules are matched.
 


@@ -3146,9 +3152,10 @@ exp:    @dots{}
               else
                 @{
                   $$ = 1;
               else
                 @{
                   $$ = 1;

-                  printf("Division by zero, l%d,c%d-l%d,c%d",
-                         @@3.first_line, @@3.first_column,
-                         @@3.last_line, @@3.last_column);
+                  fprintf (stderr,
+                           "Division by zero, l%d,c%d-l%d,c%d",
+                           @@3.first_line, @@3.first_column,
+                           @@3.last_line, @@3.last_column);

                 @}
             @}
 @end group
                 @}
             @}
 @end group


@@ -3172,9 +3179,10 @@ exp:    @dots{}
               else
                 @{
                   $$ = 1;
               else
                 @{
                   $$ = 1;

-                  printf("Division by zero, l%d,c%d-l%d,c%d",
-                         @@3.first_line, @@3.first_column,
-                         @@3.last_line, @@3.last_column);
+                  fprintf (stderr,
+                           "Division by zero, l%d,c%d-l%d,c%d",
+                           @@3.first_line, @@3.first_column,
+                           @@3.last_line, @@3.last_column);

                 @}
             @}
 @end group
                 @}
             @}
 @end group


@@ -3208,11 +3216,11 @@ By default, @code{YYLLOC_DEFAULT} is defined this way for simple
 
 @example
 @group
 
 @example
 @group

-#define YYLLOC_DEFAULT(Current, Rhs, N)          \
-  Current.first_line   = Rhs[1].first_line;      \
-  Current.first_column = Rhs[1].first_column;    \
-  Current.last_line    = Rhs[N].last_line;       \
-  Current.last_column  = Rhs[N].last_column;
+# define YYLLOC_DEFAULT(Current, Rhs, N)               \
+   ((Current).first_line   = (Rhs)[1].first_line,      \
+    (Current).first_column = (Rhs)[1].first_column,    \
+    (Current).last_line    = (Rhs)[N].last_line,       \
+    (Current).last_column  = (Rhs)[N].last_column)

 @end group
 @end example
 
 @end group
 @end example
 


@@ -3221,11 +3229,11 @@ and like this for @acronym{GLR} parsers:
 
 @example
 @group
 
 @example
 @group

-#define YYLLOC_DEFAULT(Current, Rhs, N)          \
-  Current.first_line   = YYRHSLOC(Rhs,1).first_line;      \
-  Current.first_column = YYRHSLOC(Rhs,1).first_column;    \
-  Current.last_line    = YYRHSLOC(Rhs,N).last_line;       \
-  Current.last_column  = YYRHSLOC(Rhs,N).last_column;
+# define YYLLOC_DEFAULT(yyCurrent, yyRhs, YYN)                 \
+   ((yyCurrent).first_line = YYRHSLOC(yyRhs, 1).first_line,    \
+    (yyCurrent).first_column = YYRHSLOC(yyRhs, 1).first_column,        \
+    (yyCurrent).last_line = YYRHSLOC(yyRhs, YYN).last_line,    \
+    (yyCurrent).last_column  = YYRHSLOC(yyRhs, YYN).last_column)

 @end group
 @end example
 
 @end group
 @end example
 


@@ -3239,6 +3247,12 @@ result) should be modified by @code{YYLLOC_DEFAULT}.
 @item
 For consistency with semantic actions, valid indexes for the location
 array range from 1 to @var{n}.
 @item
 For consistency with semantic actions, valid indexes for the location
 array range from 1 to @var{n}.

+
+@item
+Your macro should parenthesize its arguments, if need be, since the
+actual arguments may not be surrounded by parentheses.  Also, your
+macro should expand to something that can be used as a single
+statement when it is followed by a semicolon.

 @end itemize
 
 @node Declarations
 @end itemize
 
 @node Declarations


@@ -3495,7 +3509,7 @@ is called when a symbol is thrown away.
 Declare that the @var{code} must be invoked for each of the
 @var{symbols} that will be discarded by the parser.  The @var{code}
 should use @code{$$} to designate the semantic value associated to the
 Declare that the @var{code} must be invoked for each of the
 @var{symbols} that will be discarded by the parser.  The @var{code}
 should use @code{$$} to designate the semantic value associated to the

-@var{symbols}.  The additional parser parameters are also avaible
+@var{symbols}.  The additional parser parameters are also available

 (@pxref{Parser Function, , The Parser Function @code{yyparse}}).
 
 @strong{Warning:} as of Bison 1.875, this feature is still considered as
 (@pxref{Parser Function, , The Parser Function @code{yyparse}}).
 
 @strong{Warning:} as of Bison 1.875, this feature is still considered as


@@ -3671,9 +3685,16 @@ Declare a terminal symbol (token type name) that is left-associative
 
 @deffn {Directive} %nonassoc
 Declare a terminal symbol (token type name) that is nonassociative
 
 @deffn {Directive} %nonassoc
 Declare a terminal symbol (token type name) that is nonassociative

-(using it in a way that would be associative is a syntax error)
-@end deffn

 (@pxref{Precedence Decl, ,Operator Precedence}).
 (@pxref{Precedence Decl, ,Operator Precedence}).

+Using it in a way that would be associative is a syntax error.
+@end deffn
+
+@ifset defaultprec
+@deffn {Directive} %default-prec
+Assign a precedence to rules lacking an explicit @code{%prec} modifier
+(@pxref{Contextual Precedence, ,Context-Dependent Precedence}).
+@end deffn
+@end ifset

 
 @deffn {Directive} %type
 Declare the type of semantic values for a nonterminal symbol
 
 @deffn {Directive} %type
 Declare the type of semantic values for a nonterminal symbol


@@ -3745,6 +3766,14 @@ and so on.  @xref{Multiple Parsers, ,Multiple Parsers in the Same
 Program}.
 @end deffn
 
 Program}.
 @end deffn
 

+@ifset defaultprec
+@deffn {Directive} %no-default-prec
+Do not assign a precedence to rules lacking an explicit @code{%prec}
+modifier (@pxref{Contextual Precedence, ,Context-Dependent
+Precedence}).
+@end deffn
+@end ifset
+

 @deffn {Directive} %no-parser
 Do not include any C code in the parser file; generate tables only.  The
 parser file contains just @code{#define} directives and static variable
 @deffn {Directive} %no-parser
 Do not include any C code in the parser file; generate tables only.  The
 parser file contains just @code{#define} directives and static variable


@@ -4843,6 +4872,28 @@ exp:    @dots{}
 @end group
 @end example
 
 @end group
 @end example
 

+@ifset defaultprec
+If you forget to append @code{%prec UMINUS} to the rule for unary
+minus, Bison silently assumes that minus has its usual precedence.
+This kind of problem can be tricky to debug, since one typically
+discovers the mistake only by testing the code.
+
+The @code{%no-default-prec;} declaration makes it easier to discover
+this kind of problem systematically.  It causes rules that lack a
+@code{%prec} modifier to have no precedence, even if the last terminal
+symbol mentioned in their components has a declared precedence.
+
+If @code{%no-default-prec;} is in effect, you must specify @code{%prec}
+for all rules that participate in precedence conflict resolution.
+Then you will see any shift/reduce conflict until you tell Bison how
+to resolve it, either by changing your grammar or by adding an
+explicit precedence.  This will probably add declarations to the
+grammar, but it helps to protect against incorrect rule precedences.
+
+The effect of @code{%no-default-prec;} can be reversed by giving
+@code{%default-prec;}, which is the default.
+@end ifset
+

 @node Parser States
 @section Parser States
 @cindex finite-state machine
 @node Parser States
 @section Parser States
 @cindex finite-state machine


@@ -6354,8 +6405,10 @@ are addressed.
 
 @menu
 * Parser Stack Overflow::      Breaking the Stack Limits
 
 @menu
 * Parser Stack Overflow::      Breaking the Stack Limits

-* How Can I Reset @code{yyparse}::    @code{yyparse} Keeps some State
+* How Can I Reset the Parser:: @code{yyparse} Keeps some State

 * Strings are Destroyed::      @code{yylval} Loses Track of Strings
 * Strings are Destroyed::      @code{yylval} Loses Track of Strings

+* C++ Parsers::                Compiling Parsers with C++ Compilers
+* Implementing Loops::         Control Flow in the Calculator

 @end menu
 
 @node Parser Stack Overflow
 @end menu
 
 @node Parser Stack Overflow


@@ -6369,29 +6422,29 @@ message.  What can I do?
 This question is already addressed elsewhere, @xref{Recursion,
 ,Recursive Rules}.
 
 This question is already addressed elsewhere, @xref{Recursion,
 ,Recursive Rules}.
 

-@node How Can I Reset @code{yyparse}
-@section How Can I Reset @code{yyparse}
+@node How Can I Reset the Parser
+@section How Can I Reset the Parser

 
 

-The following phenomenon gives raise to several incarnations,
-resulting in the following typical questions:
+The following phenomenon has several symptoms, resulting in the
+following typical questions:

 
 @display
 I invoke @code{yyparse} several times, and on correct input it works
 properly; but when a parse error is found, all the other calls fail
 
 @display
 I invoke @code{yyparse} several times, and on correct input it works
 properly; but when a parse error is found, all the other calls fail

-too.  How can I reset @code{yyparse}'s error flag?
+too.  How can I reset the error flag of @code{yyparse}?

 @end display
 
 @noindent
 or
 
 @display
 @end display
 
 @noindent
 or
 
 @display

-My parser includes support for a @samp{#include} like feature, in
+My parser includes support for an @samp{#include}-like feature, in

 which case I run @code{yyparse} from @code{yyparse}.  This fails
 although I did specify I needed a @code{%pure-parser}.
 @end display
 
 which case I run @code{yyparse} from @code{yyparse}.  This fails
 although I did specify I needed a @code{%pure-parser}.
 @end display
 

-These problems are not related to Bison itself, but with the Lex
-generated scanners.  Because these scanners use large buffers for
+These problems typically come not from Bison itself, but from
+Lex-generated scanners.  Because these scanners use large buffers for

 speed, they might not notice a change of input file.  As a
 demonstration, consider the following source file,
 @file{first-line.l}:
 speed, they might not notice a change of input file.  As a
 demonstration, consider the following source file,
 @file{first-line.l}:


@@ -6405,20 +6458,20 @@ demonstration, consider the following source file,
 .*\n    ECHO; return 1;
 %%
 int
 .*\n    ECHO; return 1;
 %%
 int

-yyparse (const char *file)
+yyparse (char const *file)

 {
   yyin = fopen (file, "r");
   if (!yyin)
     exit (2);
   /* One token only. */
   yylex ();
 {
   yyin = fopen (file, "r");
   if (!yyin)
     exit (2);
   /* One token only. */
   yylex ();

-  if (!fclose (yyin))
+  if (fclose (yyin) != 0)

     exit (3);
   return 0;
 }
 
 int
     exit (3);
   return 0;
 }
 
 int

-main ()
+main (void)

 {
   yyparse ("input");
   yyparse ("input");
 {
   yyparse ("input");
   yyparse ("input");


@@ -6435,7 +6488,7 @@ input:2: World!
 @end verbatim
 
 @noindent
 @end verbatim
 
 @noindent

-then instead of getting twice the first line, you get:
+then instead of getting the first line twice, you get:

 
 @example
 $ @kbd{flex -ofirst-line.c first-line.l}
 
 @example
 $ @kbd{flex -ofirst-line.c first-line.l}


@@ -6445,12 +6498,15 @@ input:1: Hello,
 input:2: World!
 @end example
 
 input:2: World!
 @end example
 

-Therefore, whenever you change @code{yyin}, you must tell the Lex
-generated scanner to discard its current buffer, and to switch to the
-new one.  This depends upon your implementation of Lex, see its
-documentation for more.  For instance, in the case of Flex, a simple
-call @samp{yyrestart (yyin)} suffices after each change to
-@code{yyin}.
+Therefore, whenever you change @code{yyin}, you must tell the
+Lex-generated scanner to discard its current buffer and switch to the
+new one.  This depends upon your implementation of Lex; see its
+documentation for more.  For Flex, it suffices to call
+@samp{YY_FLUSH_BUFFER} after each change to @code{yyin}.  If your
+Flex-generated scanner needs to read from several input streams to
+handle features like include files, you might consider using Flex
+functions like @samp{yy_switch_to_buffer} that manipulate multiple
+input buffers.

 
 @node Strings are Destroyed
 @section Strings are Destroyed
 
 @node Strings are Destroyed
 @section Strings are Destroyed


@@ -6511,6 +6567,59 @@ $ @kbd{printf 'one\ntwo\n' | ./split-lines}
 @end example
 
 
 @end example
 
 

+@node C++ Parsers
+@section C++ Parsers
+
+@display
+How can I generate parsers in C++?
+@end display
+
+We are working on a C++ output for Bison, but unfortunately, for lack
+of time, the skeleton is not finished.  It is functional, but in
+numerous respects, it will require additional work which @emph{might}
+break backward compatibility.  Since the skeleton for C++ is not
+documented, we do not consider ourselves bound to this interface,
+nevertheless, as much as possible we will try to keep compatibility.
+
+Another possibility is to use the regular C parsers, and to compile
+them with a C++ compiler.  This works properly, provided that you bear
+some simple C++ rules in mind, such as not including ``real classes''
+(i.e., structure with constructors) in unions.  Therefore, in the
+@code{%union}, use pointers to classes, or better yet, a single
+pointer type to the root of your lexical/syntactic hierarchy.
+
+
+@node Implementing Loops
+@section Implementing Loops
+
+@display
+My simple calculator supports variables, assignments, and functions,
+but how can I implement loops?
+@end display
+
+Although very pedagogical, the examples included in the document blur
+the distinction to make between the parser---whose job is to recover
+the structure of a text and to transmit it to subsequent modules of
+the program---and the processing (such as the execution) of this
+structure.  This works well with so called straight line programs,
+i.e., precisely those that have a straightforward execution model:
+execute simple instructions one after the others.
+
+@cindex abstract syntax tree
+@cindex @acronym{AST}
+If you want a richer model, you will probably need to use the parser
+to construct a tree that does represent the structure it has
+recovered; this tree is usually called the @dfn{abstract syntax tree},
+or @dfn{@acronym{AST}} for short.  Then, walking through this tree,
+traversing it in various ways, will enable treatments such as its
+execution or its translation, which will result in an interpreter or a
+compiler.
+
+This topic is way beyond the scope of this manual, and the reader is
+invited to consult the dedicated literature.
+
+
+

 @c ================================================= Table of Symbols
 
 @node Table of Symbols
 @c ================================================= Table of Symbols
 
 @node Table of Symbols


@@ -6716,6 +6825,14 @@ parsing.  @xref{Parser Function, ,The Parser Function @code{yyparse}}.
 Equip the parser for debugging.  @xref{Decl Summary}.
 @end deffn
 
 Equip the parser for debugging.  @xref{Decl Summary}.
 @end deffn
 

+@ifset defaultprec
+@deffn {Directive} %default-prec
+Assign a precedence to rules that lack an explicit @samp{%prec}
+modifier.  @xref{Contextual Precedence, ,Context-Dependent
+Precedence}.
+@end deffn
+@end ifset
+

 @deffn {Directive} %defines
 Bison declaration to create a header file meant for the scanner.
 @xref{Decl Summary}.
 @deffn {Directive} %defines
 Bison declaration to create a header file meant for the scanner.
 @xref{Decl Summary}.


@@ -6769,6 +6886,14 @@ function is applied to the two semantic values to get a single result.
 Bison declaration to rename the external symbols.  @xref{Decl Summary}.
 @end deffn
 
 Bison declaration to rename the external symbols.  @xref{Decl Summary}.
 @end deffn
 

+@ifset defaultprec
+@deffn {Directive} %no-default-prec
+Do not assign a precedence to rules that lack an explicit @samp{%prec}
+modifier.  @xref{Contextual Precedence, ,Context-Dependent
+Precedence}.
+@end deffn
+@end ifset
+

 @deffn {Directive} %no-lines
 Bison declaration to avoid generating @code{#line} directives in the
 parser file.  @xref{Decl Summary}.
 @deffn {Directive} %no-lines
 Bison declaration to avoid generating @code{#line} directives in the
 parser file.  @xref{Decl Summary}.


@@ -7052,3 +7177,33 @@ grammatically indivisible.  The piece of text it represents is a token.
 @printindex cp
 
 @bye
 @printindex cp
 
 @bye

+
+@c LocalWords: texinfo setfilename settitle setchapternewpage finalout
+@c LocalWords: ifinfo smallbook shorttitlepage titlepage GPL FIXME iftex
+@c LocalWords: akim fn cp syncodeindex vr tp synindex dircategory direntry
+@c LocalWords: ifset vskip pt filll insertcopying sp ISBN Etienne Suvasa
+@c LocalWords: ifnottex yyparse detailmenu GLR RPN Calc var Decls Rpcalc
+@c LocalWords: rpcalc Lexer Gen Comp Expr ltcalc mfcalc Decl Symtab yylex
+@c LocalWords: yyerror pxref LR yylval cindex dfn LALR samp gpl BNF xref
+@c LocalWords: const int paren ifnotinfo AC noindent emph expr stmt findex
+@c LocalWords: glr YYSTYPE TYPENAME prog dprec printf decl init stmtMerge
+@c LocalWords: pre STDC GNUC endif yy YY alloca lf stddef stdlib YYDEBUG
+@c LocalWords: NUM exp subsubsection kbd Ctrl ctype EOF getchar isdigit
+@c LocalWords: ungetc stdin scanf sc calc ulator ls lm cc NEG prec yyerrok
+@c LocalWords: longjmp fprintf stderr preg yylloc YYLTYPE cos ln
+@c LocalWords: smallexample symrec val tptr FNCT fnctptr func struct sym
+@c LocalWords: fnct putsym getsym fname arith fncts atan ptr malloc sizeof
+@c LocalWords: strlen strcpy fctn strcmp isalpha symbuf realloc isalnum
+@c LocalWords: ptypes itype YYPRINT trigraphs yytname expseq vindex dtype
+@c LocalWords: Rhs YYRHSLOC LE nonassoc op deffn typeless typefull yynerrs
+@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
+@c LocalWords: YYEMPTY 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
+@c LocalWords: YYPRINTF infile ypp yxx outfile itemx vcg tex leaderfill
+@c LocalWords: hbox hss hfill tt ly yyin fopen fclose ofirst gcc ll
+@c LocalWords: yyrestart nbar yytext fst snd osplit ntwo strdup AST
+@c LocalWords: YYSTACK DVI fdl printindex