X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/fef4cb511e07b026e31b2791c3998515bd36bb0e..22fccf958f542d321740f6718611912ca5fec985:/doc/bison.texinfo diff --git a/doc/bison.texinfo b/doc/bison.texinfo index 9332050e..a6e2ee37 100644 --- a/doc/bison.texinfo +++ b/doc/bison.texinfo @@ -39,7 +39,7 @@ 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, 2003, +Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1995, 1998, 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc. @quotation @@ -284,7 +284,10 @@ Invoking Bison Frequently Asked Questions * Parser Stack Overflow:: Breaking the Stack Limits +* How Can I Reset the Parser:: @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 @@ -1412,7 +1415,7 @@ here is the definition we will use: void yyerror (char const *s) @{ - printf ("%s\n", s); + fprintf (stderr, "%s\n", s); @} @end group @end example @@ -3079,8 +3082,6 @@ 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. -@c (terminal or not) ? - The way locations are handled is defined by providing a data type, and actions to take when rules are matched. @@ -3145,9 +3146,10 @@ exp: @dots{} else @{ $$ = 1; - printf("Division by zero, l%d,c%d-l%d,c%d", - @@3.first_line, @@3.first_column, - @@3.last_line, @@3.last_column); + fprintf (stderr, + "Division by zero, l%d,c%d-l%d,c%d", + @@3.first_line, @@3.first_column, + @@3.last_line, @@3.last_column); @} @} @end group @@ -3171,9 +3173,10 @@ exp: @dots{} else @{ $$ = 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 @@ -3207,11 +3210,11 @@ By default, @code{YYLLOC_DEFAULT} is defined this way for simple @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 @@ -3220,11 +3223,11 @@ and like this for @acronym{GLR} parsers: @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 @@ -3238,6 +3241,12 @@ 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 +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 @@ -3494,7 +3503,7 @@ 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 -@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 @@ -3670,9 +3679,14 @@ Declare a terminal symbol (token type name) that is left-associative @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}). +Using it in a way that would be associative is a syntax error. +@end deffn + +@deffn {Directive} %default-prec +Assign a precedence to rules lacking an explicit @code{%prec} modifier +(@pxref{Contextual Precedence, ,Context-Dependent Precedence}). +@end deffn @deffn {Directive} %type Declare the type of semantic values for a nonterminal symbol @@ -3744,6 +3758,12 @@ and so on. @xref{Multiple Parsers, ,Multiple Parsers in the Same Program}. @end deffn +@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 + @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 @@ -4842,6 +4862,26 @@ exp: @dots{} @end group @end example +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. + @node Parser States @section Parser States @cindex finite-state machine @@ -6353,7 +6393,10 @@ are addressed. @menu * Parser Stack Overflow:: Breaking the Stack Limits +* How Can I Reset the Parser:: @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 @@ -6367,11 +6410,97 @@ message. What can I do? This question is already addressed elsewhere, @xref{Recursion, ,Recursive Rules}. +@node How Can I Reset the Parser +@section How Can I Reset the Parser + +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 losses track of +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 @@ -6426,6 +6555,59 @@ $ @kbd{printf 'one\ntwo\n' | ./split-lines} @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 @@ -6631,6 +6813,12 @@ parsing. @xref{Parser Function, ,The Parser Function @code{yyparse}}. Equip the parser for debugging. @xref{Decl Summary}. @end deffn +@deffn {Directive} %default-prec +Assign a precedence to rules that lack an explicit @samp{%prec} +modifier. @xref{Contextual Precedence, ,Context-Dependent +Precedence}. +@end deffn + @deffn {Directive} %defines Bison declaration to create a header file meant for the scanner. @xref{Decl Summary}. @@ -6684,6 +6872,12 @@ 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 +@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 + @deffn {Directive} %no-lines Bison declaration to avoid generating @code{#line} directives in the parser file. @xref{Decl Summary}. @@ -6967,3 +7161,33 @@ 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