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
* 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
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
* 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
@node How Can I Reset @code{yyparse}
@section How Can I Reset @code{yyparse}
-The following phenomenon gives raise to several incarnations,
-resulting in the following typical questions:
+The following phenomenon has several symptoms, resulting in the
+following typical questions:
@display
I invoke @code{yyparse} several times, and on correct input it works
properly; but when a parse error is found, all the other calls fail
-too. How can I reset @code{yyparse}'s error flag?
+too. How can I reset the error flag of @code{yyparse}?
@end display
@noindent
or
@display
-My parser includes support for a @samp{#include} like feature, in
+My parser includes support for an @samp{#include}-like feature, in
which case I run @code{yyparse} from @code{yyparse}. This fails
although I did specify I needed a @code{%pure-parser}.
@end display
-These problems are not related to Bison itself, but with the Lex
-generated scanners. Because these scanners use large buffers for
+These problems typically come not from Bison itself, but from
+Lex-generated scanners. Because these scanners use large buffers for
speed, they might not notice a change of input file. As a
demonstration, consider the following source file,
@file{first-line.l}:
.*\n ECHO; return 1;
%%
int
-yyparse (const char *file)
+yyparse (char const *file)
{
yyin = fopen (file, "r");
if (!yyin)
exit (2);
/* One token only. */
yylex ();
- if (!fclose (yyin))
+ if (fclose (yyin) != 0)
exit (3);
return 0;
}
int
-main ()
+main (void)
{
yyparse ("input");
yyparse ("input");
@end verbatim
@noindent
-then instead of getting twice the first line, you get:
+then instead of getting the first line twice, you get:
@example
$ @kbd{flex -ofirst-line.c first-line.l}
input:2: World!
@end example
-Therefore, whenever you change @code{yyin}, you must tell the Lex
-generated scanner to discard its current buffer, and to switch to the
-new one. This depends upon your implementation of Lex, see its
-documentation for more. For instance, in the case of Flex, a simple
-call @samp{yyrestart (yyin)} suffices after each change to
-@code{yyin}.
+Therefore, whenever you change @code{yyin}, you must tell the
+Lex-generated scanner to discard its current buffer and switch to the
+new one. This depends upon your implementation of Lex; see its
+documentation for more. For Flex, it suffices to call
+@samp{YY_FLUSH_BUFFER} after each change to @code{yyin}. If your
+Flex-generated scanner needs to read from several input streams to
+handle features like include files, you might consider using Flex
+functions like @samp{yy_switch_to_buffer} that manipulate multiple
+input buffers.
@node Strings are Destroyed
@section Strings are Destroyed
@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
@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
projects / bison.git / blobdiff