X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/1c0c3e955d14f01df1089eb575b79058a1d08d37..637fa3f83edca74df6a9d834ffe7bfd4d7468793:/doc/bison.texinfo?ds=sidebyside diff --git a/doc/bison.texinfo b/doc/bison.texinfo index f9e18e23..d09f42a8 100644 --- a/doc/bison.texinfo +++ b/doc/bison.texinfo @@ -40,7 +40,7 @@ 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, -1999, 2000, 2001, 2002 Free Software Foundation, Inc. +1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc. @quotation Permission is granted to copy, distribute and/or modify this document @@ -119,7 +119,8 @@ Reference sections: * Copying This Manual:: License for copying this manual. * Index:: Cross-references to the text. -@detailmenu --- The Detailed Node Listing --- +@detailmenu + --- The Detailed Node Listing --- The Concepts of Bison @@ -130,6 +131,8 @@ The Concepts of Bison a semantic value (the value of an integer, the name of an identifier, etc.). * Semantic Actions:: Each rule can have an action containing C code. +* GLR Parsers:: Writing parsers for general context-free languages +* Locations Overview:: Tracking Locations. * Bison Parser:: What are Bison's input and output, how is the output used? * Stages:: Stages in writing and running Bison grammars. @@ -143,8 +146,8 @@ Examples Operator precedence is introduced. * Simple Error Recovery:: Continuing after syntax errors. * Location Tracking Calc:: Demonstrating the use of @@@var{n} and @@$. -* Multi-function Calc:: Calculator with memory and trig functions. - It uses multiple data-types for semantic values. +* Multi-function Calc:: Calculator with memory and trig functions. + It uses multiple data-types for semantic values. * Exercises:: Ideas for improving the multi-function calculator. Reverse Polish Notation Calculator @@ -182,15 +185,16 @@ Bison Grammar Files * Rules:: How to write grammar rules. * Recursion:: Writing recursive rules. * Semantics:: Semantic values and actions. +* Locations:: Locations and actions. * Declarations:: All kinds of Bison declarations are described here. * Multiple Parsers:: Putting more than one Bison parser in one program. Outline of a Bison Grammar -* Prologue:: Syntax and usage of the prologue (declarations section). +* Prologue:: Syntax and usage of the prologue. * Bison Declarations:: Syntax and usage of the Bison declarations section. * Grammar Rules:: Syntax and usage of the grammar rules section. -* Epilogue:: Syntax and usage of the epilogue (additional code section). +* Epilogue:: Syntax and usage of the epilogue. Defining Language Semantics @@ -202,12 +206,19 @@ Defining Language Semantics This says when, why and how to use the exceptional action in the middle of a rule. +Tracking Locations + +* Location Type:: Specifying a data type for locations. +* Actions and Locations:: Using locations in actions. +* Location Default Action:: Defining a general way to compute locations. + Bison Declarations * Token Decl:: Declaring terminal symbols. * Precedence Decl:: Declaring terminals with precedence and associativity. * 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. * Start Decl:: Specifying the start symbol. * Pure Decl:: Requesting a reentrant parser. @@ -226,9 +237,9 @@ The Lexical Analyzer Function @code{yylex} * Calling Convention:: How @code{yyparse} calls @code{yylex}. * Token Values:: How @code{yylex} must return the semantic value of the token it has read. -* Token Positions:: How @code{yylex} must return the text position +* Token Locations:: How @code{yylex} must return the text location (line number, etc.) of the token, if the - actions want that. + actions want that. * Pure Calling:: How the calling convention differs in a pure parser (@pxref{Pure Decl, ,A Pure (Reentrant) Parser}). @@ -258,7 +269,7 @@ Handling Context Dependencies * Tie-in Recovery:: Lexical tie-ins have implications for how error recovery rules must be written. -Understanding or Debugging Your Parser +Debugging Your Parser * Understanding:: Understanding the structure of your parser. * Tracing:: Tracing the execution of your parser. @@ -268,11 +279,15 @@ Invoking Bison * Bison Options:: All the options described in detail, in alphabetical order by short options. * Option Cross Key:: Alphabetical list of long options. -* VMS Invocation:: Bison command syntax on @acronym{VMS}. +* Yacc Library:: Yacc-compatible @code{yylex} and @code{main}. Frequently Asked Questions * Parser Stack Overflow:: Breaking the Stack Limits +* How Can I Reset @code{yyparse}:: @code{yyparse} Keeps some State +* 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 @@ -412,42 +427,41 @@ more information on this. @cindex generalized @acronym{LR} (@acronym{GLR}) parsing @cindex ambiguous grammars @cindex non-deterministic parsing -Parsers for @acronym{LALR}(1) grammars are @dfn{deterministic}, -meaning roughly that -the next grammar rule to apply at any point in the input is uniquely -determined by the preceding input and a fixed, finite portion (called -a @dfn{look-ahead}) of the remaining input. -A context-free grammar can be @dfn{ambiguous}, meaning that -there are multiple ways to apply the grammar rules to get the some inputs. -Even unambiguous grammars can be @dfn{non-deterministic}, meaning that no -fixed look-ahead always suffices to determine the next grammar rule to apply. -With the proper declarations, Bison is also able to parse these more general -context-free grammars, using a technique known as @acronym{GLR} parsing (for -Generalized @acronym{LR}). Bison's @acronym{GLR} parsers are able to -handle any context-free -grammar for which the number of possible parses of any given string -is finite. + +Parsers for @acronym{LALR}(1) grammars are @dfn{deterministic}, meaning +roughly that the next grammar rule to apply at any point in the input is +uniquely determined by the preceding input and a fixed, finite portion +(called a @dfn{look-ahead}) of the remaining input. A context-free +grammar can be @dfn{ambiguous}, meaning that there are multiple ways to +apply the grammar rules to get the some inputs. Even unambiguous +grammars can be @dfn{non-deterministic}, meaning that no fixed +look-ahead always suffices to determine the next grammar rule to apply. +With the proper declarations, Bison is also able to parse these more +general context-free grammars, using a technique known as @acronym{GLR} +parsing (for Generalized @acronym{LR}). Bison's @acronym{GLR} parsers +are able to handle any context-free grammar for which the number of +possible parses of any given string is finite. @cindex symbols (abstract) @cindex token @cindex syntactic grouping @cindex grouping, syntactic -In the formal grammatical rules for a language, each kind of syntactic unit -or grouping is named by a @dfn{symbol}. Those which are built by grouping -smaller constructs according to grammatical rules are called +In the formal grammatical rules for a language, each kind of syntactic +unit or grouping is named by a @dfn{symbol}. Those which are built by +grouping smaller constructs according to grammatical rules are called @dfn{nonterminal symbols}; those which can't be subdivided are called @dfn{terminal symbols} or @dfn{token types}. We call a piece of input corresponding to a single terminal symbol a @dfn{token}, and a piece corresponding to a single nonterminal symbol a @dfn{grouping}. We can use the C language as an example of what symbols, terminal and -nonterminal, mean. The tokens of C are identifiers, constants (numeric and -string), and the various keywords, arithmetic operators and punctuation -marks. So the terminal symbols of a grammar for C include `identifier', -`number', `string', plus one symbol for each keyword, operator or -punctuation mark: `if', `return', `const', `static', `int', `char', -`plus-sign', `open-brace', `close-brace', `comma' and many more. (These -tokens can be subdivided into characters, but that is a matter of +nonterminal, mean. The tokens of C are identifiers, constants (numeric +and string), and the various keywords, arithmetic operators and +punctuation marks. So the terminal symbols of a grammar for C include +`identifier', `number', `string', plus one symbol for each keyword, +operator or punctuation mark: `if', `return', `const', `static', `int', +`char', `plus-sign', `open-brace', `close-brace', `comma' and many more. +(These tokens can be subdivided into characters, but that is a matter of lexicography, not grammar.) Here is a simple C function subdivided into tokens: @@ -642,28 +656,28 @@ from the values of the two subexpressions. @cindex conflicts @cindex shift/reduce conflicts -In some grammars, there will be cases where Bison's standard @acronym{LALR}(1) -parsing algorithm cannot decide whether to apply a certain grammar rule -at a given point. That is, it may not be able to decide (on the basis -of the input read so far) which of two possible reductions (applications -of a grammar rule) applies, or whether to apply a reduction or read more -of the input and apply a reduction later in the input. These are known -respectively as @dfn{reduce/reduce} conflicts (@pxref{Reduce/Reduce}), -and @dfn{shift/reduce} conflicts (@pxref{Shift/Reduce}). - -To use a grammar that is not easily modified to be @acronym{LALR}(1), a more -general parsing algorithm is sometimes necessary. If you include +In some grammars, there will be cases where Bison's standard +@acronym{LALR}(1) parsing algorithm cannot decide whether to apply a +certain grammar rule at a given point. That is, it may not be able to +decide (on the basis of the input read so far) which of two possible +reductions (applications of a grammar rule) applies, or whether to apply +a reduction or read more of the input and apply a reduction later in the +input. These are known respectively as @dfn{reduce/reduce} conflicts +(@pxref{Reduce/Reduce}), and @dfn{shift/reduce} conflicts +(@pxref{Shift/Reduce}). + +To use a grammar that is not easily modified to be @acronym{LALR}(1), a +more general parsing algorithm is sometimes necessary. If you include @code{%glr-parser} among the Bison declarations in your file -(@pxref{Grammar Outline}), the result will be a Generalized -@acronym{LR} (@acronym{GLR}) -parser. These parsers handle Bison grammars that contain no unresolved -conflicts (i.e., after applying precedence declarations) identically to -@acronym{LALR}(1) parsers. However, when faced with unresolved -shift/reduce and reduce/reduce conflicts, @acronym{GLR} parsers use -the simple expedient of doing -both, effectively cloning the parser to follow both possibilities. Each -of the resulting parsers can again split, so that at any given time, -there can be any number of possible parses being explored. The parsers +(@pxref{Grammar Outline}), the result will be a Generalized @acronym{LR} +(@acronym{GLR}) parser. These parsers handle Bison grammars that +contain no unresolved conflicts (i.e., after applying precedence +declarations) identically to @acronym{LALR}(1) parsers. However, when +faced with unresolved shift/reduce and reduce/reduce conflicts, +@acronym{GLR} parsers use the simple expedient of doing both, +effectively cloning the parser to follow both possibilities. Each of +the resulting parsers can again split, so that at any given time, there +can be any number of possible parses being explored. The parsers proceed in lockstep; that is, all of them consume (shift) a given input symbol before any of them proceed to the next. Each of the cloned parsers eventually meets one of two possible fates: either it runs into @@ -686,7 +700,10 @@ Let's consider an example, vastly simplified from a C++ grammar. @example %@{ - #define YYSTYPE const char* + #include + #define YYSTYPE char const * + int yylex (void); + void yyerror (char const *); %@} %token TYPENAME ID @@ -784,7 +801,8 @@ stmt : expr ';' %merge and define the @code{stmtMerge} function as: @example -static YYSTYPE stmtMerge (YYSTYPE x0, YYSTYPE x1) +static YYSTYPE +stmtMerge (YYSTYPE x0, YYSTYPE x1) @{ printf (" "); return ""; @@ -797,7 +815,7 @@ in the C declarations at the beginning of the file: @example %@{ - #define YYSTYPE const char* + #define YYSTYPE char const * static YYSTYPE stmtMerge (YYSTYPE x0, YYSTYPE x1); %@} @end example @@ -810,16 +828,43 @@ as both an @code{expr} and a @code{decl}, and print "x" y z + T x T y z + = @end example +@sp 1 + +@cindex @code{incline} +@cindex @acronym{GLR} parsers and @code{inline} +The @acronym{GLR} parsers require a compiler for @acronym{ISO} C89 or +later. In addition, they use the @code{inline} keyword, which is not +C89, but is C99 and is a common extension in pre-C99 compilers. It is +up to the user of these parsers to handle +portability issues. For instance, if using Autoconf and the Autoconf +macro @code{AC_C_INLINE}, a mere + +@example +%@{ + #include +%@} +@end example + +@noindent +will suffice. Otherwise, we suggest + +@example +%@{ + #if __STDC_VERSION__ < 199901 && ! defined __GNUC__ && ! defined inline + #define inline + #endif +%@} +@end example @node Locations Overview @section Locations @cindex location -@cindex textual position -@cindex position, textual +@cindex textual location +@cindex location, textual Many applications, like interpreters or compilers, have to produce verbose and useful error messages. To achieve this, one must be able to keep track of -the @dfn{textual position}, or @dfn{location}, of each syntactic construct. +the @dfn{textual location}, or @dfn{location}, of each syntactic construct. Bison provides a mechanism for handling these locations. Each token has a semantic value. In a similar fashion, each token has an @@ -967,6 +1012,9 @@ in every Bison grammar file to separate the sections. The prologue may define types and variables used in the actions. You can also use preprocessor commands to define macros used there, and use @code{#include} to include header files that do any of these things. +You need to declare the lexical analyzer @code{yylex} and the error +printer @code{yyerror} here, along with any other global identifiers +used by the actions in the grammar rules. The Bison declarations declare the names of the terminal and nonterminal symbols, and may also describe operator precedence and the data types of @@ -975,10 +1023,9 @@ semantic values of various symbols. The grammar rules define how to construct each nonterminal symbol from its parts. -The epilogue can contain any code you want to use. Often the definition of -the lexical analyzer @code{yylex} goes here, plus subroutines called by the -actions in the grammar rules. In a simple program, all the rest of the -program can go here. +The epilogue can contain any code you want to use. Often the +definitions of functions declared in the prologue go here. In a +simple program, all the rest of the program can go here. @node Examples @chapter Examples @@ -1045,8 +1092,10 @@ calculator. As in C, comments are placed between @samp{/*@dots{}*/}. /* Reverse polish notation calculator. */ %@{ -#define YYSTYPE double -#include + #define YYSTYPE double + #include + int yylex (void); + void yyerror (char const *); %@} %token NUM @@ -1055,7 +1104,7 @@ calculator. As in C, comments are placed between @samp{/*@dots{}*/}. @end example The declarations section (@pxref{Prologue, , The prologue}) contains two -preprocessor directives. +preprocessor directives and two forward declarations. The @code{#define} directive defines the macro @code{YYSTYPE}, thus specifying the C data type for semantic values of both tokens and @@ -1068,6 +1117,12 @@ which is a floating point number. The @code{#include} directive is used to declare the exponentiation function @code{pow}. +The forward declarations for @code{yylex} and @code{yyerror} are +needed because the C language requires that functions be declared +before they are used. These functions will be defined in the +epilogue, but the parser calls them so they must be declared in the +prologue. + The second section, Bison declarations, provides information to Bison about the token types (@pxref{Bison Declarations, ,The Bison Declarations Section}). Each terminal symbol that is not a @@ -1088,18 +1143,18 @@ input: /* empty */ ; line: '\n' - | exp '\n' @{ printf ("\t%.10g\n", $1); @} + | exp '\n' @{ printf ("\t%.10g\n", $1); @} ; -exp: NUM @{ $$ = $1; @} - | exp exp '+' @{ $$ = $1 + $2; @} - | exp exp '-' @{ $$ = $1 - $2; @} - | exp exp '*' @{ $$ = $1 * $2; @} - | exp exp '/' @{ $$ = $1 / $2; @} - /* Exponentiation */ - | exp exp '^' @{ $$ = pow ($1, $2); @} - /* Unary minus */ - | exp 'n' @{ $$ = -$1; @} +exp: NUM @{ $$ = $1; @} + | exp exp '+' @{ $$ = $1 + $2; @} + | exp exp '-' @{ $$ = $1 - $2; @} + | exp exp '*' @{ $$ = $1 * $2; @} + | exp exp '/' @{ $$ = $1 / $2; @} + /* Exponentiation */ + | exp exp '^' @{ $$ = pow ($1, $2); @} + /* Unary minus */ + | exp 'n' @{ $$ = -$1; @} ; %% @end example @@ -1348,7 +1403,7 @@ main (void) When @code{yyparse} detects a syntax error, it calls the error reporting function @code{yyerror} to print an error message (usually but not -always @code{"parse error"}). It is up to the programmer to supply +always @code{"syntax error"}). It is up to the programmer to supply @code{yyerror} (@pxref{Interface, ,Parser C-Language Interface}), so here is the definition we will use: @@ -1356,8 +1411,9 @@ here is the definition we will use: @group #include +/* Called by yyparse on error. */ void -yyerror (const char *s) /* Called by yyparse on error. */ +yyerror (char const *s) @{ printf ("%s\n", s); @} @@ -1457,23 +1513,25 @@ parentheses nested to arbitrary depth. Here is the Bison code for @file{calc.y}, an infix desk-top calculator. @example -/* Infix notation calculator--calc */ +/* Infix notation calculator. */ %@{ -#define YYSTYPE double -#include + #define YYSTYPE double + #include + #include + int yylex (void); + void yyerror (char const *); %@} -/* Bison Declarations */ +/* Bison declarations. */ %token NUM %left '-' '+' %left '*' '/' %left NEG /* negation--unary minus */ -%right '^' /* exponentiation */ +%right '^' /* exponentiation */ -/* Grammar follows */ -%% -input: /* empty string */ +%% /* The grammar follows. */ +input: /* empty */ | input line ; @@ -1558,7 +1616,7 @@ line: '\n' @end example This addition to the grammar allows for simple error recovery in the -event of a parse error. If an expression that cannot be evaluated is +event of a syntax error. If an expression that cannot be evaluated is read, the error will be recognized by the third rule for @code{line}, and parsing will continue. (The @code{yyerror} function is still called upon to print its message as well.) The action executes the statement @@ -1603,8 +1661,10 @@ the same as the declarations for the infix notation calculator. /* Location tracking calculator. */ %@{ -#define YYSTYPE int -#include + #define YYSTYPE int + #include + int yylex (void); + void yyerror (char const *); %@} /* Bison declarations. */ @@ -1615,7 +1675,7 @@ the same as the declarations for the infix notation calculator. %left NEG %right '^' -%% /* Grammar follows */ +%% /* The grammar follows. */ @end example @noindent @@ -1706,11 +1766,15 @@ int yylex (void) @{ int c; +@end group +@group /* Skip white space. */ while ((c = getchar ()) == ' ' || c == '\t') ++yylloc.last_column; +@end group +@group /* Step. */ yylloc.first_line = yylloc.last_line; yylloc.first_column = yylloc.last_column; @@ -1832,28 +1896,32 @@ Note that multiple assignment and nested function calls are permitted. Here are the C and Bison declarations for the multi-function calculator. @smallexample +@group %@{ -#include /* For math functions, cos(), sin(), etc. */ -#include "calc.h" /* Contains definition of `symrec' */ + #include /* For math functions, cos(), sin(), etc. */ + #include "calc.h" /* Contains definition of `symrec'. */ + int yylex (void); + void yyerror (char const *); %@} +@end group +@group %union @{ -double val; /* For returning numbers. */ -symrec *tptr; /* For returning symbol-table pointers */ + double val; /* For returning numbers. */ + symrec *tptr; /* For returning symbol-table pointers. */ @} - -%token NUM /* Simple double precision number */ -%token VAR FNCT /* Variable and Function */ +@end group +%token NUM /* Simple double precision number. */ +%token VAR FNCT /* Variable and Function. */ %type exp +@group %right '=' %left '-' '+' %left '*' '/' -%left NEG /* Negation--unary minus */ -%right '^' /* Exponentiation */ - -/* Grammar follows */ - -%% +%left NEG /* negation--unary minus */ +%right '^' /* exponentiation */ +@end group +%% /* The grammar follows. */ @end smallexample The above grammar introduces only two new features of the Bison language. @@ -1886,16 +1954,21 @@ Most of them are copied directly from @code{calc}; three rules, those which mention @code{VAR} or @code{FNCT}, are new. @smallexample +@group input: /* empty */ | input line ; +@end group +@group line: '\n' | exp '\n' @{ printf ("\t%.10g\n", $1); @} | error '\n' @{ yyerrok; @} ; +@end group +@group exp: NUM @{ $$ = $1; @} | VAR @{ $$ = $1->value.var; @} | VAR '=' exp @{ $$ = $3; $1->value.var = $3; @} @@ -1908,7 +1981,8 @@ exp: NUM @{ $$ = $1; @} | exp '^' exp @{ $$ = pow ($1, $3); @} | '(' exp ')' @{ $$ = $2; @} ; -/* End of grammar */ +@end group +/* End of grammar. */ %% @end smallexample @@ -1927,31 +2001,33 @@ provides for either functions or variables to be placed in the table. @smallexample @group -/* Function type. */ +/* Function type. */ typedef double (*func_t) (double); +@end group -/* Data type for links in the chain of symbols. */ +@group +/* Data type for links in the chain of symbols. */ struct symrec @{ - char *name; /* name of symbol */ + char *name; /* name of symbol */ int type; /* type of symbol: either VAR or FNCT */ union @{ - double var; /* value of a VAR */ - func_t fnctptr; /* value of a FNCT */ + double var; /* value of a VAR */ + func_t fnctptr; /* value of a FNCT */ @} value; - struct symrec *next; /* link field */ + struct symrec *next; /* link field */ @}; @end group @group typedef struct symrec symrec; -/* The symbol table: a chain of `struct symrec'. */ +/* The symbol table: a chain of `struct symrec'. */ extern symrec *sym_table; -symrec *putsym (const char *, func_t); -symrec *getsym (const char *); +symrec *putsym (char const *, func_t); +symrec *getsym (char const *); @end group @end smallexample @@ -1960,33 +2036,27 @@ function that initializes the symbol table. Here it is, and @code{init_table} as well: @smallexample -@group #include -int -main (void) -@{ - init_table (); - return yyparse (); -@} -@end group - @group +/* Called by yyparse on error. */ void -yyerror (const char *s) /* Called by yyparse on error. */ +yyerror (char const *s) @{ printf ("%s\n", s); @} +@end group +@group struct init @{ - char *fname; - double (*fnct)(double); + char const *fname; + double (*fnct) (double); @}; @end group @group -struct init arith_fncts[] = +struct init const arith_fncts[] = @{ "sin", sin, "cos", cos, @@ -1996,9 +2066,11 @@ struct init arith_fncts[] = "sqrt", sqrt, 0, 0 @}; +@end group +@group /* The symbol table: a chain of `struct symrec'. */ -symrec *sym_table = (symrec *) 0; +symrec *sym_table; @end group @group @@ -2015,6 +2087,15 @@ init_table (void) @} @} @end group + +@group +int +main (void) +@{ + init_table (); + return yyparse (); +@} +@end group @end smallexample By simply editing the initialization list and adding the necessary include @@ -2029,7 +2110,7 @@ found, a pointer to that symbol is returned; otherwise zero is returned. @smallexample symrec * -putsym (char *sym_name, int sym_type) +putsym (char const *sym_name, int sym_type) @{ symrec *ptr; ptr = (symrec *) malloc (sizeof (symrec)); @@ -2043,7 +2124,7 @@ putsym (char *sym_name, int sym_type) @} symrec * -getsym (const char *sym_name) +getsym (char const *sym_name) @{ symrec *ptr; for (ptr = sym_table; ptr != (symrec *) 0; @@ -2072,7 +2153,9 @@ operators in @code{yylex}. @smallexample @group #include +@end group +@group int yylex (void) @{ @@ -2120,7 +2203,7 @@ yylex (void) if (i == length) @{ length *= 2; - symbuf = (char *)realloc (symbuf, length + 1); + symbuf = (char *) realloc (symbuf, length + 1); @} /* Add this character to the buffer. */ symbuf[i++] = c; @@ -2199,7 +2282,7 @@ appropriate delimiters: @example %@{ -@var{Prologue} + @var{Prologue} %@} @var{Bison declarations} @@ -2222,7 +2305,7 @@ continues until end of line. * Epilogue:: Syntax and usage of the epilogue. @end menu -@node Prologue, Bison Declarations, , Grammar Outline +@node Prologue @subsection The prologue @cindex declarations section @cindex Prologue @@ -2246,8 +2329,8 @@ can be done with two @var{Prologue} blocks, one before and one after the @smallexample %@{ -#include -#include "ptypes.h" + #include + #include "ptypes.h" %@} %union @{ @@ -2256,8 +2339,8 @@ can be done with two @var{Prologue} blocks, one before and one after the @} %@{ -static void yyprint(FILE *, int, YYSTYPE); -#define YYPRINT(F, N, L) yyprint(F, N, L) + static void print_token_value (FILE *, int, YYSTYPE); + #define YYPRINT(F, N, L) print_token_value (F, N, L) %@} @dots{} @@ -2285,7 +2368,7 @@ There must always be at least one grammar rule, and the first @samp{%%} (which precedes the grammar rules) may never be omitted even if it is the first thing in the file. -@node Epilogue, , Grammar Rules, Grammar Outline +@node Epilogue @subsection The epilogue @cindex additional C code section @cindex epilogue @@ -2295,14 +2378,17 @@ The @var{Epilogue} is copied verbatim to the end of the parser file, just as the @var{Prologue} is copied to the beginning. This is the most convenient place to put anything that you want to have in the parser file but which need not come before the definition of @code{yyparse}. For example, the -definitions of @code{yylex} and @code{yyerror} often go here. +definitions of @code{yylex} and @code{yyerror} often go here. Because +C requires functions to be declared before being used, you often need +to declare functions like @code{yylex} and @code{yyerror} in the Prologue, +even if you define them int he Epilogue. @xref{Interface, ,Parser C-Language Interface}. If the last section is empty, you may omit the @samp{%%} that separates it from the grammar rules. -The Bison parser itself contains many static variables whose names start -with @samp{yy} and many macros whose names start with @samp{YY}. It is a +The Bison parser itself contains many macros and identifiers whose +names start with @samp{yy} or @samp{YY}, so it is a good idea to avoid using any such names (except those documented in this manual) in the epilogue of the grammar file. @@ -2749,11 +2835,11 @@ a-or-b: 'a'|'b' @{ a_or_b_found = 1; @}; @cindex default action If you don't specify an action for a rule, Bison supplies a default: -@w{@code{$$ = $1}.} Thus, the value of the first symbol in the rule becomes -the value of the whole rule. Of course, the default rule is valid only -if the two data types match. There is no meaningful default action for -an empty rule; every empty rule must have an explicit action unless the -rule's value does not matter. +@w{@code{$$ = $1}.} Thus, the value of the first symbol in the rule +becomes the value of the whole rule. Of course, the default action is +valid only if the two data types match. There is no meaningful default +action for an empty rule; every empty rule must have an explicit action +unless the rule's value does not matter. @code{$@var{n}} with @var{n} zero or negative is allowed for reference to tokens and groupings on the stack @emph{before} those that match the @@ -2989,8 +3075,8 @@ actually does to implement mid-rule actions. @node Locations @section Tracking Locations @cindex location -@cindex textual position -@cindex position, textual +@cindex textual location +@cindex location, textual Though grammar rules and semantic actions are enough to write a fully functional parser, it can be useful to process some additional information, @@ -3020,13 +3106,13 @@ When @code{YYLTYPE} is not defined, Bison uses a default structure type with four members: @example -struct +typedef struct YYLTYPE @{ int first_line; int first_column; int last_line; int last_column; -@} +@} YYLTYPE; @end example @node Actions and Locations @@ -3104,17 +3190,23 @@ Actually, actions are not the best place to compute locations. Since locations are much more general than semantic values, there is room in the output parser to redefine the default action to take for each rule. The @code{YYLLOC_DEFAULT} macro is invoked each time a rule is -matched, before the associated action is run. +matched, before the associated action is run. It is also invoked +while processing a syntax error, to compute the error's location. Most of the time, this macro is general enough to suppress location dedicated code from semantic actions. The @code{YYLLOC_DEFAULT} macro takes three parameters. The first one is -the location of the grouping (the result of the computation). The second one -is an array holding locations of all right hand side elements of the rule -being matched. The last one is the size of the right hand side rule. +the location of the grouping (the result of the computation). When a +rule is matched, the second parameter is an array holding locations of +all right hand side elements of the rule being matched, and the third +parameter is the size of the rule's right hand side. When processing +a syntax error, the second parameter is an array holding locations of +the symbols that were discarded during error processing, and the third +parameter is the number of discarded symbols. -By default, it is defined this way for simple @acronym{LALR}(1) parsers: +By default, @code{YYLLOC_DEFAULT} is defined this way for simple +@acronym{LALR}(1) parsers: @example @group @@ -3175,6 +3267,7 @@ Grammars}). * Precedence Decl:: Declaring terminals with precedence and associativity. * 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. * Start Decl:: Specifying the start symbol. * Pure Decl:: Requesting a reentrant parser. @@ -3334,7 +3427,23 @@ This says that the two alternative types are @code{double} and @code{symrec in the @code{%token} and @code{%type} declarations to pick one of the types for a terminal or nonterminal symbol (@pxref{Type Decl, ,Nonterminal Symbols}). -Note that, unlike making a @code{union} declaration in C, you do not write +As an extension to @acronym{POSIX}, a tag is allowed after the +@code{union}. For example: + +@example +@group +%union value @{ + double val; + symrec *tptr; +@} +@end group +@end example + +specifies the union tag @code{value}, so the corresponding C type is +@code{union value}. If you do not specify a tag, it defaults to +@code{YYSTYPE}. + +Note that, unlike making a @code{union} declaration in C, you need not write a semicolon after the closing brace. @node Type Decl @@ -3365,6 +3474,71 @@ use the same @code{<@var{type}>} construction in a declaration for the terminal symbol. All kinds of token declarations allow @code{<@var{type}>}. +@node Destructor Decl +@subsection Freeing Discarded Symbols +@cindex freeing discarded symbols +@findex %destructor + +Some symbols can be discarded by the parser, typically during error +recovery (@pxref{Error Recovery}). Basically, during error recovery, +embarrassing symbols already pushed on the stack, and embarrassing +tokens coming from the rest of the file are thrown away until the parser +falls on its feet. If these symbols convey heap based information, this +memory is lost. While this behavior is tolerable for batch parsers, +such as in compilers, it is unacceptable for parsers that can +possibility ``never end'' such as shells, or implementations of +communication protocols. + +The @code{%destructor} directive allows for the definition of code that +is called when a symbol is thrown away. + +@deffn {Directive} %destructor @{ @var{code} @} @var{symbols} +@findex %destructor +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{$$} to designate the semantic value associated to the +@var{symbols}. The additional parser parameters are also available +(@pxref{Parser Function, , The Parser Function @code{yyparse}}). + +@strong{Warning:} as of Bison 1.875, this feature is still considered as +experimental, as there was not enough user feedback. In particular, +the syntax might still change. +@end deffn + +For instance: + +@smallexample +%union +@{ + char *string; +@} +%token STRING +%type string +%destructor @{ free ($$); @} STRING string +@end smallexample + +@noindent +guarantees that when a @code{STRING} or a @code{string} will be discarded, +its associated memory will be freed. + +Note that in the future, Bison might also consider that right hand side +members that are not mentioned in the action can be destroyed. For +instance, in: + +@smallexample +comment: "/*" STRING "*/"; +@end smallexample + +@noindent +the parser is entitled to destroy the semantic value of the +@code{string}. Of course, this will not apply to the default action; +compare: + +@smallexample +typeless: string; // $$ = $1 does not apply; $1 is destroyed. +typefull: string; // $$ = $1 applies, $1 is not destroyed. +@end smallexample + @node Expect Decl @subsection Suppressing Conflict Warnings @cindex suppressing conflict warnings @@ -3388,7 +3562,7 @@ The declaration looks like this: Here @var{n} is a decimal integer. The declaration says there should be no warning if there are @var{n} shift/reduce conflicts and no -reduce/reduce conflicts. An error, instead of the usual warning, is +reduce/reduce conflicts. The usual warning is given if there are either more or fewer conflicts, or if there are any reduce/reduce conflicts. @@ -3410,9 +3584,9 @@ Add an @code{%expect} declaration, copying the number @var{n} from the number which Bison printed. @end itemize -Now Bison will stop annoying you about the conflicts you have checked, but -it will warn you again if changes in the grammar result in additional -conflicts. +Now Bison will stop annoying you if you do not change the number of +conflicts, but it will warn you again if changes in the grammar result +in more or fewer conflicts. @node Start Decl @subsection The Start-Symbol @@ -3477,53 +3651,60 @@ valid grammar. Here is a summary of the declarations used to define a grammar: -@table @code -@item %union +@deffn {Directive} %union Declare the collection of data types that semantic values may have (@pxref{Union Decl, ,The Collection of Value Types}). +@end deffn -@item %token +@deffn {Directive} %token Declare a terminal symbol (token type name) with no precedence or associativity specified (@pxref{Token Decl, ,Token Type Names}). +@end deffn -@item %right +@deffn {Directive} %right Declare a terminal symbol (token type name) that is right-associative (@pxref{Precedence Decl, ,Operator Precedence}). +@end deffn -@item %left +@deffn {Directive} %left Declare a terminal symbol (token type name) that is left-associative (@pxref{Precedence Decl, ,Operator Precedence}). +@end deffn -@item %nonassoc +@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}). -@item %type +@deffn {Directive} %type Declare the type of semantic values for a nonterminal symbol (@pxref{Type Decl, ,Nonterminal Symbols}). +@end deffn -@item %start +@deffn {Directive} %start Specify the grammar's start symbol (@pxref{Start Decl, ,The Start-Symbol}). +@end deffn -@item %expect +@deffn {Directive} %expect Declare the expected number of shift-reduce conflicts (@pxref{Expect Decl, ,Suppressing Conflict Warnings}). -@end table +@end deffn + @sp 1 @noindent In order to change the behavior of @command{bison}, use the following directives: -@table @code -@item %debug +@deffn {Directive} %debug In the parser file, define the macro @code{YYDEBUG} to 1 if it is not already defined, so that the debugging facilities are compiled. +@end deffn @xref{Tracing, ,Tracing Your Parser}. -@item %defines +@deffn {Directive} %defines Write an extra output file containing macro definitions for the token type names defined in the grammar and the semantic value type @code{YYSTYPE}, as well as a few @code{extern} variable declarations. @@ -3535,27 +3716,27 @@ This output file is essential if you wish to put the definition of @code{yylex} in a separate source file, because @code{yylex} needs to be able to refer to token type codes and the variable @code{yylval}. @xref{Token Values, ,Semantic Values of Tokens}. +@end deffn + +@deffn {Directive} %destructor +Specifying how the parser should reclaim the memory associated to +discarded symbols. @xref{Destructor Decl, , Freeing Discarded Symbols}. +@end deffn -@item %file-prefix="@var{prefix}" +@deffn {Directive} %file-prefix="@var{prefix}" Specify a prefix to use for all Bison output file names. The names are chosen as if the input file were named @file{@var{prefix}.y}. +@end deffn -@c @item %header-extension -@c Specify the extension of the parser header file generated when -@c @code{%define} or @samp{-d} are used. -@c -@c For example, a grammar file named @file{foo.ypp} and containing a -@c @code{%header-extension .hh} directive will produce a header file -@c named @file{foo.tab.hh} - -@item %locations +@deffn {Directive} %locations Generate the code processing the locations (@pxref{Action Features, ,Special Features for Use in Actions}). This mode is enabled as soon as the grammar uses the special @samp{@@@var{n}} tokens, but if your grammar does not use it, using @samp{%locations} allows for more -accurate parse error messages. +accurate syntax error messages. +@end deffn -@item %name-prefix="@var{prefix}" +@deffn {Directive} %name-prefix="@var{prefix}" Rename the external symbols used in the parser so that they start with @var{prefix} instead of @samp{yy}. The precise list of symbols renamed is @code{yyparse}, @code{yylex}, @code{yyerror}, @code{yynerrs}, @@ -3564,8 +3745,9 @@ possible @code{yylloc}. For example, if you use @samp{%name-prefix="c_"}, the names become @code{c_parse}, @code{c_lex}, and so on. @xref{Multiple Parsers, ,Multiple Parsers in the Same Program}. +@end deffn -@item %no-parser +@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 declarations. @@ -3573,34 +3755,32 @@ declarations. This option also tells Bison to write the C code for the grammar actions into a file named @file{@var{filename}.act}, in the form of a brace-surrounded body fit for a @code{switch} statement. +@end deffn -@item %no-lines +@deffn {Directive} %no-lines Don't generate any @code{#line} preprocessor commands in the parser file. Ordinarily Bison writes these commands in the parser file so that the C compiler and debuggers will associate errors and object code with your source file (the grammar file). This directive causes them to associate errors with the parser file, treating it an independent source file in its own right. +@end deffn -@item %output="@var{filename}" +@deffn {Directive} %output="@var{filename}" Specify the @var{filename} for the parser file. +@end deffn -@item %pure-parser +@deffn {Directive} %pure-parser Request a pure (reentrant) parser program (@pxref{Pure Decl, ,A Pure (Reentrant) Parser}). +@end deffn -@c @item %source-extension -@c Specify the extension of the parser output file. -@c -@c For example, a grammar file named @file{foo.yy} and containing a -@c @code{%source-extension .cpp} directive will produce a parser file -@c named @file{foo.tab.cpp} - -@item %token-table +@deffn {Directive} %token-table Generate an array of token names in the parser file. The name of the array is @code{yytname}; @code{yytname[@var{i}]} is the name of the token whose internal Bison token code number is @var{i}. The first -three elements of @code{yytname} are always @code{"$end"}, +three elements of @code{yytname} correspond to the predefined tokens +@code{"$end"}, @code{"error"}, and @code{"$undefined"}; after these come the symbols defined in the grammar file. @@ -3628,21 +3808,19 @@ The number of grammar rules, @item YYNSTATES The number of parser states (@pxref{Parser States}). @end table +@end deffn -@item %verbose +@deffn {Directive} %verbose Write an extra output file containing verbose descriptions of the parser states and what is done for each type of look-ahead token in that state. @xref{Understanding, , Understanding Your Parser}, for more information. +@end deffn - - -@item %yacc +@deffn {Directive} %yacc Pretend the option @option{--yacc} was given, i.e., imitate Yacc, including its naming conventions. @xref{Bison Options}, for more. -@end table - - +@end deffn @node Multiple Parsers @@ -3732,19 +3910,20 @@ If you use a reentrant parser, you can optionally pass additional parameter information to it in a reentrant way. To do so, use the declaration @code{%parse-param}: -@deffn {Directive} %parse-param @var{argument-declaration} @var{argument-name} +@deffn {Directive} %parse-param @{@var{argument-declaration}@} @findex %parse-param -Declare that @code{argument-name} is an additional @code{yyparse} -argument. This argument is also passed to @code{yyerror}. The -@var{argument-declaration} is used when declaring functions or -prototypes. +Declare that an argument declared by @code{argument-declaration} is an +additional @code{yyparse} argument. +The @var{argument-declaration} is used when declaring +functions or prototypes. The last identifier in +@var{argument-declaration} must be the argument name. @end deffn Here's an example. Write this in the parser: @example -%parse-param "int *nastiness" "nastiness" -%parse-param "int *randomness" "randomness" +%parse-param @{int *nastiness@} +%parse-param @{int *randomness@} @end example @noindent @@ -3789,7 +3968,7 @@ that need it. @xref{Invocation, ,Invoking Bison}. * Calling Convention:: How @code{yyparse} calls @code{yylex}. * Token Values:: How @code{yylex} must return the semantic value of the token it has read. -* Token Positions:: How @code{yylex} must return the text position +* Token Locations:: How @code{yylex} must return the text location (line number, etc.) of the token, if the actions want that. * Pure Calling:: How the calling convention differs @@ -3922,8 +4101,8 @@ then the code in @code{yylex} might look like this: @end group @end example -@node Token Positions -@subsection Textual Positions of Tokens +@node Token Locations +@subsection Textual Locations of Tokens @vindex yylloc If you are using the @samp{@@@var{n}}-feature (@pxref{Locations, , @@ -3966,7 +4145,7 @@ yylex (YYSTYPE *lvalp, YYLTYPE *llocp) @end example If the grammar file does not use the @samp{@@} constructs to refer to -textual positions, then the type @code{YYLTYPE} will not be defined. In +textual locations, then the type @code{YYLTYPE} will not be defined. In this case, omit the second argument; @code{yylex} will be called with only one argument. @@ -3975,18 +4154,18 @@ If you wish to pass the additional parameter data to @code{yylex}, use @code{%lex-param} just like @code{%parse-param} (@pxref{Parser Function}). -@deffn {Directive} lex-param @var{argument-declaration} @var{argument-name} +@deffn {Directive} lex-param @{@var{argument-declaration}@} @findex %lex-param -Declare that @code{argument-name} is an additional @code{yylex} -argument. +Declare that @code{argument-declaration} is an additional @code{yylex} +argument declaration. @end deffn For instance: @example -%parse-param "int *nastiness" "nastiness" -%lex-param "int *nastiness" "nastiness" -%parse-param "int *randomness" "randomness" +%parse-param @{int *nastiness@} +%lex-param @{int *nastiness@} +%parse-param @{int *randomness@} @end example @noindent @@ -4019,7 +4198,7 @@ int yyparse (int *nastiness, int *randomness); @cindex parse error @cindex syntax error -The Bison parser detects a @dfn{parse error} or @dfn{syntax error} +The Bison parser detects a @dfn{syntax error} or @dfn{parse error} whenever it reads a token which cannot satisfy any syntax rule. An action in the grammar can also explicitly proclaim an error, using the macro @code{YYERROR} (@pxref{Action Features, ,Special Features for Use @@ -4028,14 +4207,14 @@ in Actions}). The Bison parser expects to report the error by calling an error reporting function named @code{yyerror}, which you must supply. It is called by @code{yyparse} whenever a syntax error is found, and it -receives one argument. For a parse error, the string is normally -@w{@code{"parse error"}}. +receives one argument. For a syntax error, the string is normally +@w{@code{"syntax error"}}. @findex %error-verbose If you invoke the directive @code{%error-verbose} in the Bison declarations section (@pxref{Bison Declarations, ,The Bison Declarations Section}), then Bison provides a more verbose and specific error message -string instead of just plain @w{@code{"parse error"}}. +string instead of just plain @w{@code{"syntax error"}}. The parser can detect one other kind of error: stack overflow. This happens when the input contains constructions that are very deeply @@ -4050,7 +4229,7 @@ The following definition suffices in simple programs: @example @group void -yyerror (const char *s) +yyerror (char const *s) @{ @end group @group @@ -4071,15 +4250,15 @@ parsers, but not for the Yacc parser, for historical reasons. I.e., if @code{yyerror} are: @example -void yyerror (const char *msg); /* Yacc parsers. */ -void yyerror (YYLTYPE *locp, const char *msg); /* GLR parsers. */ +void yyerror (char const *msg); /* Yacc parsers. */ +void yyerror (YYLTYPE *locp, char const *msg); /* GLR parsers. */ @end example -If @samp{%parse-param "int *nastiness" "nastiness"} is used, then: +If @samp{%parse-param @{int *nastiness@}} is used, then: @example -void yyerror (int *randomness, const char *msg); /* Yacc parsers. */ -void yyerror (int *randomness, const char *msg); /* GLR parsers. */ +void yyerror (int *nastiness, char const *msg); /* Yacc parsers. */ +void yyerror (int *nastiness, char const *msg); /* GLR parsers. */ @end example Finally, GLR and Yacc parsers share the same @code{yyerror} calling @@ -4092,10 +4271,10 @@ convention of @code{yylex} @emph{and} the calling convention of %locations /* Pure yylex. */ %pure-parser -%lex-param "int *nastiness" "nastiness" +%lex-param @{int *nastiness@} /* Pure yyparse. */ -%parse-param "int *nastiness" "nastiness" -%parse-param "int *randomness" "randomness" +%parse-param @{int *nastiness@} +%parse-param @{int *randomness@} @end example @noindent @@ -4106,14 +4285,20 @@ int yylex (YYSTYPE *lvalp, YYLTYPE *llocp, int *nastiness); int yyparse (int *nastiness, int *randomness); void yyerror (YYLTYPE *locp, int *nastiness, int *randomness, - const char *msg); + char const *msg); @end example @noindent -Please, note that the prototypes are only indications of how the code -produced by Bison will use @code{yyerror}; you still have freedom on the -exit value, and even on making @code{yyerror} a variadic function. It -is precisely to enable this that the message is always passed last. +The prototypes are only indications of how the code produced by Bison +uses @code{yyerror}. Bison-generated code always ignores the returned +value, so @code{yyerror} can return any type, including @code{void}. +Also, @code{yyerror} can be a variadic function; that is why the +message is always passed last. + +Traditionally @code{yyerror} returns an @code{int} that is always +ignored, but this is purely for historical reasons, and @code{void} is +preferable since it more accurately describes the return type for +@code{yyerror}. @vindex yynerrs The variable @code{yynerrs} contains the number of syntax errors @@ -4129,34 +4314,39 @@ then it is a local variable which only the actions can access. Here is a table of Bison constructs, variables and macros that are useful in actions. -@table @samp -@item $$ +@deffn {Variable} $$ Acts like a variable that contains the semantic value for the grouping made by the current rule. @xref{Actions}. +@end deffn -@item $@var{n} +@deffn {Variable} $@var{n} Acts like a variable that contains the semantic value for the @var{n}th component of the current rule. @xref{Actions}. +@end deffn -@item $<@var{typealt}>$ +@deffn {Variable} $<@var{typealt}>$ Like @code{$$} but specifies alternative @var{typealt} in the union specified by the @code{%union} declaration. @xref{Action Types, ,Data Types of Values in Actions}. +@end deffn -@item $<@var{typealt}>@var{n} +@deffn {Variable} $<@var{typealt}>@var{n} Like @code{$@var{n}} but specifies alternative @var{typealt} in the union specified by the @code{%union} declaration. @xref{Action Types, ,Data Types of Values in Actions}. +@end deffn -@item YYABORT; +@deffn {Macro} YYABORT; Return immediately from @code{yyparse}, indicating failure. @xref{Parser Function, ,The Parser Function @code{yyparse}}. +@end deffn -@item YYACCEPT; +@deffn {Macro} YYACCEPT; Return immediately from @code{yyparse}, indicating success. @xref{Parser Function, ,The Parser Function @code{yyparse}}. +@end deffn -@item YYBACKUP (@var{token}, @var{value}); +@deffn {Macro} YYBACKUP (@var{token}, @var{value}); @findex YYBACKUP Unshift a token. This macro is allowed only for rules that reduce a single value, and only when there is no look-ahead token. @@ -4171,42 +4361,49 @@ a message @samp{cannot back up} and performs ordinary error recovery. In either case, the rest of the action is not executed. +@end deffn -@item YYEMPTY +@deffn {Macro} YYEMPTY @vindex YYEMPTY Value stored in @code{yychar} when there is no look-ahead token. +@end deffn -@item YYERROR; +@deffn {Macro} YYERROR; @findex YYERROR Cause an immediate syntax error. This statement initiates error recovery just as if the parser itself had detected an error; however, it does not call @code{yyerror}, and does not print any message. If you want to print an error message, call @code{yyerror} explicitly before the @samp{YYERROR;} statement. @xref{Error Recovery}. +@end deffn -@item YYRECOVERING +@deffn {Macro} YYRECOVERING This macro stands for an expression that has the value 1 when the parser is recovering from a syntax error, and 0 the rest of the time. @xref{Error Recovery}. +@end deffn -@item yychar +@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. @xref{Look-Ahead, ,Look-Ahead Tokens}. +@end deffn -@item yyclearin; +@deffn {Macro} yyclearin; Discard the current look-ahead token. This is useful primarily in error rules. @xref{Error Recovery}. +@end deffn -@item yyerrok; +@deffn {Macro} yyerrok; Resume generating error messages immediately for subsequent syntax errors. This is useful primarily in error rules. @xref{Error Recovery}. +@end deffn -@item @@$ +@deffn {Value} @@$ @findex @@$ -Acts like a structure variable containing information on the textual position +Acts like a structure variable containing information on the textual location of the grouping made by the current rule. @xref{Locations, , Tracking Locations}. @@ -4228,14 +4425,15 @@ Tracking Locations}. @c those members. @c The use of this feature makes the parser noticeably slower. +@end deffn -@item @@@var{n} +@deffn {Value} @@@var{n} @findex @@@var{n} -Acts like a structure variable containing information on the textual position +Acts like a structure variable containing information on the textual location of the @var{n}th component of the current rule. @xref{Locations, , Tracking Locations}. +@end deffn -@end table @node Algorithm @chapter The Bison Parser Algorithm @@ -4977,6 +5175,13 @@ structure should generally be adequate. On @acronym{LALR}(1) portions of a grammar, in particular, it is only slightly slower than with the default Bison parser. +For a more detailed exposition of GLR parsers, please see: Elizabeth +Scott, Adrian Johnstone and Shamsa Sadaf Hussain, Tomita-Style +Generalised @acronym{LR} Parsers, Royal Holloway, University of +London, Department of Computer Science, TR-00-12, +@uref{http://www.cs.rhul.ac.uk/research/languages/publications/tomita_style_1.ps}, +(2000-12-24). + @node Stack Overflow @section Stack Overflow, and How to Avoid It @cindex stack overflow @@ -5028,7 +5233,7 @@ provided which addresses this issue. @cindex error recovery @cindex recovery from errors -It is not usually acceptable to have a program terminate on a parse +It is not usually acceptable to have a program terminate on a syntax error. For example, a compiler should recover sufficiently to parse the rest of the input file and check it for errors; a calculator should accept another expression. @@ -5070,15 +5275,17 @@ will be tokens to read before the next newline. So the rule is not applicable in the ordinary way. But Bison can force the situation to fit the rule, by discarding part of -the semantic context and part of the input. First it discards states and -objects from the stack until it gets back to a state in which the +the semantic context and part of the input. First it discards states +and objects from the stack until it gets back to a state in which the @code{error} token is acceptable. (This means that the subexpressions -already parsed are discarded, back to the last complete @code{stmnts}.) At -this point the @code{error} token can be shifted. Then, if the old +already parsed are discarded, back to the last complete @code{stmnts}.) +At this point the @code{error} token can be shifted. Then, if the old look-ahead token is not acceptable to be shifted next, the parser reads tokens and discards them until it finds a token which is acceptable. In -this example, Bison reads and discards input until the next newline -so that the fourth rule can apply. +this example, Bison reads and discards input until the next newline so +that the fourth rule can apply. Note that discarded symbols are +possible sources of memory leaks, see @ref{Destructor Decl, , Freeing +Discarded Symbols}, for a means to reclaim this memory. The choice of error rules in the grammar is a choice of strategies for error recovery. A simple and useful strategy is simply to skip the rest of @@ -5129,7 +5336,7 @@ 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. -For example, suppose that on a parse error, an error handling routine is +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 once again commence. The next symbol returned by the lexical scanner is probably correct. The previous look-ahead token ought to be discarded @@ -5252,7 +5459,9 @@ as an identifier if it appears in that context. Here is how you can do it: @example @group %@{ -int hexflag; + int hexflag; + int yylex (void); + void yyerror (char const *); %@} %% @dots{} @@ -5400,8 +5609,8 @@ useless: STR; @example calc.y: warning: 1 useless nonterminal and 1 useless rule calc.y:11.1-7: warning: useless nonterminal: useless -calc.y:11.8-12: warning: useless rule: useless: STR -calc.y contains 7 shift/reduce conflicts. +calc.y:11.10-12: warning: useless rule: useless: STR +calc.y: conflicts: 7 shift/reduce @end example When given @option{--report=state}, in addition to @file{calc.tab.c}, it @@ -5423,10 +5632,10 @@ Conflict in state 8 between rule 2 and token '*' resolved as shift. The next section lists states that still have conflicts. @example -State 8 contains 1 shift/reduce conflict. -State 9 contains 1 shift/reduce conflict. -State 10 contains 1 shift/reduce conflict. -State 11 contains 4 shift/reduce conflicts. +State 8 conflicts: 1 shift/reduce +State 9 conflicts: 1 shift/reduce +State 10 conflicts: 1 shift/reduce +State 11 conflicts: 4 shift/reduce @end example @noindent @@ -5516,7 +5725,7 @@ after having reduced a rule that produced an @code{exp}, the control flow jumps to state 2. If there is no such transition on a nonterminal symbol, and the lookahead is a @code{NUM}, then this token is shifted on the parse stack, and the control flow jumps to state 1. Any other -lookahead triggers a parse error.'' +lookahead triggers a syntax error.'' @cindex core, item set @cindex item set core @@ -5584,7 +5793,7 @@ because of the item @samp{exp -> exp . '+' exp}, if the lookahead if @samp{+}, it will be shifted on the parse stack, and the automaton control will jump to state 4, corresponding to the item @samp{exp -> exp '+' . exp}. Since there is no default action, any other token than -those listed above will trigger a parse error. +those listed above will trigger a syntax error. The state 3 is named the @dfn{final state}, or the @dfn{accepting state}: @@ -5638,8 +5847,8 @@ state 7 exp go to state 11 @end example -As was announced in beginning of the report, @samp{State 8 contains 1 -shift/reduce conflict}: +As was announced in beginning of the report, @samp{State 8 conflicts: +1 shift/reduce}: @example state 8 @@ -5850,15 +6059,20 @@ Here is an example of @code{YYPRINT} suitable for the multi-function calculator (@pxref{Mfcalc Decl, ,Declarations for @code{mfcalc}}): @smallexample -#define YYPRINT(file, type, value) yyprint (file, type, value) +%@{ + static void print_token_value (FILE *, int, YYSTYPE); + #define YYPRINT(file, type, value) print_token_value (file, type, value) +%@} + +@dots{} %% @dots{} %% @dots{} static void -yyprint (FILE *file, int type, YYSTYPE value) +print_token_value (FILE *file, int type, YYSTYPE value) @{ if (type == VAR) - fprintf (file, " %s", value.tptr->name); + fprintf (file, "%s", value.tptr->name); else if (type == NUM) - fprintf (file, " %d", value.val); + fprintf (file, "%d", value.val); @} @end smallexample @@ -5902,11 +6116,15 @@ bison -d -o @var{output.c++} @var{infile.y} @noindent will produce @file{output.c++} and @file{outfile.h++}. +For compatibility with @acronym{POSIX}, the standard Bison +distribution also contains a shell script called @command{yacc} that +invokes Bison with the @option{-y} option. + @menu * Bison Options:: All the options described in detail, in alphabetical order by short options. * Option Cross Key:: Alphabetical list of long options. -* VMS Invocation:: Bison command syntax on @acronym{VMS}. +* Yacc Library:: Yacc-compatible @code{yylex} and @code{main}. @end menu @node Bison Options @@ -5942,10 +6160,12 @@ Equivalent to @samp{-o y.tab.c}; the parser output file is called @file{y.tab.c}, and the other outputs are called @file{y.output} and @file{y.tab.h}. The purpose of this option is to imitate Yacc's output file name conventions. Thus, the following shell script can substitute -for Yacc: +for Yacc, and the Bison distribution contains such a script for +compatibility with @acronym{POSIX}: @example -bison -y $* +#! /bin/sh +bison -y "$@" @end example @end table @@ -6098,34 +6318,32 @@ the corresponding short option. @end example @end ifinfo -@node VMS Invocation -@section Invoking Bison under @acronym{VMS} -@cindex invoking Bison under @acronym{VMS} -@cindex @acronym{VMS} +@node Yacc Library +@section Yacc Library -The command line syntax for Bison on @acronym{VMS} is a variant of the usual -Bison command syntax---adapted to fit @acronym{VMS} conventions. +The Yacc library contains default implementations of the +@code{yyerror} and @code{main} functions. These default +implementations are normally not useful, but @acronym{POSIX} requires +them. To use the Yacc library, link your program with the +@option{-ly} option. Note that Bison's implementation of the Yacc +library is distributed under the terms of the @acronym{GNU} General +Public License (@pxref{Copying}). -To find the @acronym{VMS} equivalent for any Bison option, start with the long -option, and substitute a @samp{/} for the leading @samp{--}, and -substitute a @samp{_} for each @samp{-} in the name of the long option. -For example, the following invocation under @acronym{VMS}: +If you use the Yacc library's @code{yyerror} function, you should +declare @code{yyerror} as follows: @example -bison /debug/name_prefix=bar foo.y +int yyerror (char const *); @end example -@noindent -is equivalent to the following command under @acronym{POSIX}. +Bison ignores the @code{int} value returned by this @code{yyerror}. +If you use the Yacc library's @code{main} function, your +@code{yyparse} function should have the following type signature: @example -bison --debug --name-prefix=bar foo.y +int yyparse (void); @end example -The @acronym{VMS} file system does not permit filenames such as -@file{foo.tab.c}. In the above example, the output file -would instead be named @file{foo_tab.c}. - @c ================================================= Invoking Bison @node FAQ @@ -6138,6 +6356,10 @@ are addressed. @menu * Parser Stack Overflow:: Breaking the Stack Limits +* How Can I Reset @code{yyparse}:: @code{yyparse} Keeps some State +* 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 @@ -6151,6 +6373,204 @@ message. What can I do? This question is already addressed elsewhere, @xref{Recursion, ,Recursive Rules}. +@node How Can I Reset @code{yyparse} +@section How Can I Reset @code{yyparse} + +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 +too. How can I reset the error flag of @code{yyparse}? +@end display + +@noindent +or + +@display +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 + +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}: + +@verbatim +%{ +#include +#include +%} +%% +.*\n ECHO; return 1; +%% +int +yyparse (char const *file) +{ + yyin = fopen (file, "r"); + if (!yyin) + exit (2); + /* One token only. */ + yylex (); + if (fclose (yyin) != 0) + exit (3); + return 0; +} + +int +main (void) +{ + yyparse ("input"); + yyparse ("input"); + return 0; +} +@end verbatim + +@noindent +If the file @file{input} contains + +@verbatim +input:1: Hello, +input:2: World! +@end verbatim + +@noindent +then instead of getting the first line twice, you get: + +@example +$ @kbd{flex -ofirst-line.c first-line.l} +$ @kbd{gcc -ofirst-line first-line.c -ll} +$ @kbd{./first-line} +input:1: Hello, +input:2: World! +@end example + +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 + +@display +My parser seems to destroy old strings, or maybe it loses track of +them. Instead of reporting @samp{"foo", "bar"}, it reports +@samp{"bar", "bar"}, or even @samp{"foo\nbar", "bar"}. +@end display + +This error is probably the single most frequent ``bug report'' sent to +Bison lists, but is only concerned with a misunderstanding of the role +of scanner. Consider the following Lex code: + +@verbatim +%{ +#include +char *yylval = NULL; +%} +%% +.* yylval = yytext; return 1; +\n /* IGNORE */ +%% +int +main () +{ + /* Similar to using $1, $2 in a Bison action. */ + char *fst = (yylex (), yylval); + char *snd = (yylex (), yylval); + printf ("\"%s\", \"%s\"\n", fst, snd); + return 0; +} +@end verbatim + +If you compile and run this code, you get: + +@example +$ @kbd{flex -osplit-lines.c split-lines.l} +$ @kbd{gcc -osplit-lines split-lines.c -ll} +$ @kbd{printf 'one\ntwo\n' | ./split-lines} +"one +two", "two" +@end example + +@noindent +this is because @code{yytext} is a buffer provided for @emph{reading} +in the action, but if you want to keep it, you have to duplicate it +(e.g., using @code{strdup}). Note that the output may depend on how +your implementation of Lex handles @code{yytext}. For instance, when +given the Lex compatibility option @option{-l} (which triggers the +option @samp{%array}) Flex generates a different behavior: + +@example +$ @kbd{flex -l -osplit-lines.c split-lines.l} +$ @kbd{gcc -osplit-lines split-lines.c -ll} +$ @kbd{printf 'one\ntwo\n' | ./split-lines} +"two", "two" +@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 @@ -6158,303 +6578,353 @@ This question is already addressed elsewhere, @xref{Recursion, @cindex Bison symbols, table of @cindex symbols in Bison, table of -@table @code -@item @@$ +@deffn {Variable} @@$ In an action, the location of the left-hand side of the rule. @xref{Locations, , Locations Overview}. +@end deffn -@item @@@var{n} +@deffn {Variable} @@@var{n} In an action, the location of the @var{n}-th symbol of the right-hand side of the rule. @xref{Locations, , Locations Overview}. +@end deffn -@item $$ +@deffn {Variable} $$ In an action, the semantic value of the left-hand side of the rule. @xref{Actions}. +@end deffn -@item $@var{n} +@deffn {Variable} $@var{n} In an action, the semantic value of the @var{n}-th symbol of the right-hand side of the rule. @xref{Actions}. +@end deffn -@item $accept +@deffn {Symbol} $accept The predefined nonterminal whose only rule is @samp{$accept: @var{start} $end}, where @var{start} is the start symbol. @xref{Start Decl, , The Start-Symbol}. It cannot be used in the grammar. +@end deffn -@item $end +@deffn {Symbol} $end The predefined token marking the end of the token stream. It cannot be used in the grammar. +@end deffn -@item $undefined +@deffn {Symbol} $undefined The predefined token onto which all undefined values returned by @code{yylex} are mapped. It cannot be used in the grammar, rather, use @code{error}. +@end deffn -@item error +@deffn {Symbol} error A token name reserved for error recovery. This token may be used in grammar rules so as to allow the Bison parser to recognize an error in the grammar without halting the process. In effect, a sentence -containing an error may be recognized as valid. On a parse error, the +containing an error may be recognized as valid. On a syntax error, the token @code{error} becomes the current look-ahead token. Actions corresponding to @code{error} are then executed, and the look-ahead token is reset to the token that originally caused the violation. @xref{Error Recovery}. +@end deffn -@item YYABORT +@deffn {Macro} YYABORT Macro to pretend that an unrecoverable syntax error has occurred, by making @code{yyparse} return 1 immediately. The error reporting function @code{yyerror} is not called. @xref{Parser Function, ,The Parser Function @code{yyparse}}. +@end deffn -@item YYACCEPT +@deffn {Macro} YYACCEPT Macro to pretend that a complete utterance of the language has been read, by making @code{yyparse} return 0 immediately. @xref{Parser Function, ,The Parser Function @code{yyparse}}. +@end deffn -@item YYBACKUP +@deffn {Macro} YYBACKUP Macro to discard a value from the parser stack and fake a look-ahead token. @xref{Action Features, ,Special Features for Use in Actions}. +@end deffn -@item YYDEBUG +@deffn {Macro} YYDEBUG Macro to define to equip the parser with tracing code. @xref{Tracing, ,Tracing Your Parser}. +@end deffn -@item YYERROR +@deffn {Macro} YYERROR Macro to pretend that a syntax error has just been detected: call @code{yyerror} and then perform normal error recovery if possible (@pxref{Error Recovery}), or (if recovery is impossible) make @code{yyparse} return 1. @xref{Error Recovery}. +@end deffn -@item YYERROR_VERBOSE -An obsolete macro that you define with @code{#define} in the Bison -declarations section to request verbose, specific error message strings +@deffn {Macro} YYERROR_VERBOSE +An obsolete macro that you define with @code{#define} in the prologue +to request verbose, specific error message strings when @code{yyerror} is called. It doesn't matter what definition you use for @code{YYERROR_VERBOSE}, just whether you define it. Using @code{%error-verbose} is preferred. +@end deffn -@item YYINITDEPTH +@deffn {Macro} YYINITDEPTH Macro for specifying the initial size of the parser stack. @xref{Stack Overflow}. +@end deffn -@item YYLEX_PARAM +@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 macro is deprecated, and is supported only for Yacc like parsers. @xref{Pure Calling,, Calling Conventions for Pure Parsers}. +@end deffn -@item YYLTYPE -Macro for the data type of @code{yylloc}; a structure with four +@deffn {Type} YYLTYPE +Data type of @code{yylloc}; by default, a structure with four members. @xref{Location Type, , Data Types of Locations}. +@end deffn -@item yyltype -Default value for YYLTYPE. - -@item YYMAXDEPTH -Macro for specifying the maximum size of the parser stack. -@xref{Stack Overflow}. +@deffn {Macro} YYMAXDEPTH +Macro for specifying the maximum size of the parser stack. @xref{Stack +Overflow}. +@end deffn -@item YYPARSE_PARAM +@deffn {Macro} YYPARSE_PARAM An obsolete macro for specifying the name of a parameter that @code{yyparse} should accept. 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 -@item YYRECOVERING +@deffn {Macro} YYRECOVERING Macro whose value indicates whether the parser is recovering from a syntax error. @xref{Action Features, ,Special Features for Use in Actions}. +@end deffn -@item YYSTACK_USE_ALLOCA +@deffn {Macro} YYSTACK_USE_ALLOCA Macro used to control the use of @code{alloca}. If defined to @samp{0}, the parser will not use @code{alloca} but @code{malloc} when trying to grow its internal stacks. Do @emph{not} define @code{YYSTACK_USE_ALLOCA} to anything else. +@end deffn -@item YYSTYPE -Macro for the data type of semantic values; @code{int} by default. +@deffn {Type} YYSTYPE +Data type of semantic values; @code{int} by default. @xref{Value Type, ,Data Types of Semantic Values}. +@end deffn -@item yychar +@deffn {Variable} yychar External integer variable that contains the integer value of the current 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}. +@end deffn -@item yyclearin +@deffn {Variable} yyclearin Macro used in error-recovery rule actions. It clears the previous look-ahead token. @xref{Error Recovery}. +@end deffn -@item yydebug +@deffn {Variable} yydebug External integer variable set to zero by default. If @code{yydebug} is given a nonzero value, the parser will output information on input symbols and parser action. @xref{Tracing, ,Tracing Your Parser}. +@end deffn -@item yyerrok +@deffn {Macro} yyerrok Macro to cause parser to recover immediately to its normal mode -after a parse error. @xref{Error Recovery}. +after a syntax error. @xref{Error Recovery}. +@end deffn -@item yyerror -User-supplied function to be called by @code{yyparse} on error. The -function receives one argument, a pointer to a character string -containing an error message. @xref{Error Reporting, ,The Error +@deffn {Function} yyerror +User-supplied function to be called by @code{yyparse} on error. +@xref{Error Reporting, ,The Error Reporting Function @code{yyerror}}. +@end deffn -@item yylex +@deffn {Function} yylex User-supplied lexical analyzer function, called with no arguments to get the next token. @xref{Lexical, ,The Lexical Analyzer Function @code{yylex}}. +@end deffn -@item yylval +@deffn {Variable} yylval 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 @code{yylex}.) @xref{Token Values, ,Semantic Values of Tokens}. +@end deffn -@item yylloc +@deffn {Variable} yylloc 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 @code{yylex}.) You can ignore this variable if you don't use the -@samp{@@} feature in the grammar actions. @xref{Token Positions, -,Textual Positions of Tokens}. +@samp{@@} feature in the grammar actions. @xref{Token Locations, +,Textual Locations of Tokens}. +@end deffn -@item yynerrs -Global variable which Bison increments each time there is a parse error. +@deffn {Variable} yynerrs +Global variable which Bison increments each time there is a syntax error. (In a pure parser, it is a local variable within @code{yyparse}.) @xref{Error Reporting, ,The Error Reporting Function @code{yyerror}}. +@end deffn -@item yyparse +@deffn {Function} yyparse The parser function produced by Bison; call this function to start parsing. @xref{Parser Function, ,The Parser Function @code{yyparse}}. +@end deffn -@item %debug +@deffn {Directive} %debug Equip the parser for debugging. @xref{Decl Summary}. +@end deffn -@item %defines +@deffn {Directive} %defines Bison declaration to create a header file meant for the scanner. @xref{Decl Summary}. +@end deffn -@item %dprec +@deffn {Directive} %destructor +Specifying how the parser should reclaim the memory associated to +discarded symbols. @xref{Destructor Decl, , Freeing Discarded Symbols}. +@end deffn + +@deffn {Directive} %dprec Bison declaration to assign a precedence to a rule that is used at parse time to resolve reduce/reduce conflicts. @xref{GLR Parsers, ,Writing @acronym{GLR} Parsers}. +@end deffn -@item %error-verbose +@deffn {Directive} %error-verbose Bison declaration to request verbose, specific error message strings when @code{yyerror} is called. +@end deffn -@item %file-prefix="@var{prefix}" +@deffn {Directive} %file-prefix="@var{prefix}" Bison declaration to set the prefix of the output files. @xref{Decl Summary}. +@end deffn -@item %glr-parser +@deffn {Directive} %glr-parser Bison declaration to produce a @acronym{GLR} parser. @xref{GLR Parsers, ,Writing @acronym{GLR} Parsers}. +@end deffn -@c @item %source-extension -@c Bison declaration to specify the generated parser output file extension. -@c @xref{Decl Summary}. -@c -@c @item %header-extension -@c Bison declaration to specify the generated parser header file extension -@c if required. @xref{Decl Summary}. - -@item %left +@deffn {Directive} %left Bison declaration to assign left associativity to token(s). @xref{Precedence Decl, ,Operator Precedence}. +@end deffn -@item %lex-param "@var{argument-declaration}" "@var{argument-name}" +@deffn {Directive} %lex-param @{@var{argument-declaration}@} Bison declaration to specifying an additional parameter that @code{yylex} should accept. @xref{Pure Calling,, Calling Conventions for Pure Parsers}. +@end deffn -@item %merge +@deffn {Directive} %merge Bison declaration to assign a merging function to a rule. If there is a reduce/reduce conflict with a rule having the same merging function, the function is applied to the two semantic values to get a single result. @xref{GLR Parsers, ,Writing @acronym{GLR} Parsers}. +@end deffn -@item %name-prefix="@var{prefix}" +@deffn {Directive} %name-prefix="@var{prefix}" Bison declaration to rename the external symbols. @xref{Decl Summary}. +@end deffn -@item %no-lines +@deffn {Directive} %no-lines Bison declaration to avoid generating @code{#line} directives in the parser file. @xref{Decl Summary}. +@end deffn -@item %nonassoc +@deffn {Directive} %nonassoc Bison declaration to assign non-associativity to token(s). @xref{Precedence Decl, ,Operator Precedence}. +@end deffn -@item %output="@var{filename}" +@deffn {Directive} %output="@var{filename}" Bison declaration to set the name of the parser file. @xref{Decl Summary}. +@end deffn -@item %parse-param "@var{argument-declaration}" "@var{argument-name}" +@deffn {Directive} %parse-param @{@var{argument-declaration}@} Bison declaration to specifying an additional parameter that @code{yyparse} should accept. @xref{Parser Function,, The Parser Function @code{yyparse}}. +@end deffn -@item %prec +@deffn {Directive} %prec Bison declaration to assign a precedence to a specific rule. @xref{Contextual Precedence, ,Context-Dependent Precedence}. +@end deffn -@item %pure-parser +@deffn {Directive} %pure-parser Bison declaration to request a pure (reentrant) parser. @xref{Pure Decl, ,A Pure (Reentrant) Parser}. +@end deffn -@item %right +@deffn {Directive} %right Bison declaration to assign right associativity to token(s). @xref{Precedence Decl, ,Operator Precedence}. +@end deffn -@item %start +@deffn {Directive} %start Bison declaration to specify the start symbol. @xref{Start Decl, ,The Start-Symbol}. +@end deffn -@item %token +@deffn {Directive} %token Bison declaration to declare token(s) without specifying precedence. @xref{Token Decl, ,Token Type Names}. +@end deffn -@item %token-table +@deffn {Directive} %token-table Bison declaration to include a token name table in the parser file. @xref{Decl Summary}. +@end deffn -@item %type +@deffn {Directive} %type Bison declaration to declare nonterminals. @xref{Type Decl, ,Nonterminal Symbols}. +@end deffn -@item %union +@deffn {Directive} %union Bison declaration to specify several possible data types for semantic values. @xref{Union Decl, ,The Collection of Value Types}. -@end table +@end deffn @sp 1 These are the punctuation and delimiters used in Bison input: -@table @samp -@item %% +@deffn {Delimiter} %% Delimiter used to separate the grammar rule section from the Bison declarations section or the epilogue. @xref{Grammar Layout, ,The Overall Layout of a Bison Grammar}. +@end deffn -@item %@{ %@} +@c Don't insert spaces, or check the DVI output. +@deffn {Delimiter} %@{@var{code}%@} All code listed between @samp{%@{} and @samp{%@}} is copied directly to the output file uninterpreted. Such code forms the prologue of the input file. @xref{Grammar Outline, ,Outline of a Bison Grammar}. +@end deffn -@item /*@dots{}*/ +@deffn {Construct} /*@dots{}*/ Comment delimiters, as in C. +@end deffn -@item : +@deffn {Delimiter} : Separates a rule's result from its components. @xref{Rules, ,Syntax of Grammar Rules}. +@end deffn -@item ; +@deffn {Delimiter} ; Terminates a rule. @xref{Rules, ,Syntax of Grammar Rules}. +@end deffn -@item | +@deffn {Delimiter} | Separates alternate rules for the same result nonterminal. @xref{Rules, ,Syntax of Grammar Rules}. -@end table +@end deffn @node Glossary @appendix Glossary @@ -6559,10 +7029,6 @@ A grammar symbol standing for a grammatical construct that can be expressed through rules in terms of smaller constructs; in other words, a construct that is not a token. @xref{Symbols}. -@item Parse error -An error encountered during parsing of an input stream due to invalid -syntax. @xref{Error Recovery}. - @item Parser A function that recognizes valid sentences of a language by analyzing the syntax structure of a set of tokens passed to it from a lexical @@ -6615,6 +7081,10 @@ A data structure where symbol names and associated data are stored during parsing to allow for recognition and use of existing information in repeated uses of a symbol. @xref{Multi-function Calc}. +@item Syntax error +An error encountered during parsing of an input stream due to invalid +syntax. @xref{Error Recovery}. + @item Token A basic, grammatically indivisible unit of a language. The symbol that describes a token in the grammar is a terminal symbol. @@ -6642,3 +7112,33 @@ grammatically indivisible. The piece of text it represents is a token. @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