@subsection Running Bison to Make the Parser
@cindex running Bison (introduction)
-Before running Bison to produce a parser, we need to decide how to arrange
-all the source code in one or more source files. For such a simple example,
-the easiest thing is to put everything in one file. The definitions of
-@code{yylex}, @code{yyerror} and @code{main} go at the end, in the
-``additional C code'' section of the file (@pxref{Grammar Layout, ,The Overall Layout of a Bison Grammar}).
+Before running Bison to produce a parser, we need to decide how to
+arrange all the source code in one or more source files. For such a
+simple example, the easiest thing is to put everything in one file. The
+definitions of @code{yylex}, @code{yyerror} and @code{main} go at the
+end, in the ``additional C code'' section of the file (@pxref{Grammar
+Layout, ,The Overall Layout of a Bison Grammar}).
For a large project, you would probably have several source files, and use
@code{make} to arrange to recompile them.
@end example
@noindent
-The functions @code{yylex}, @code{yyerror} and @code{main} can be the same
-as before.
+The functions @code{yylex}, @code{yyerror} and @code{main} can be the
+same as before.
There are two important new features shown in this code.
Up to this point, this manual has not addressed the issue of @dfn{error
recovery}---how to continue parsing after the parser detects a syntax
-error. All we have handled is error reporting with @code{yyerror}. Recall
-that by default @code{yyparse} returns after calling @code{yyerror}. This
-means that an erroneous input line causes the calculator program to exit.
-Now we show how to rectify this deficiency.
+error. All we have handled is error reporting with @code{yyerror}.
+Recall that by default @code{yyparse} returns after calling
+@code{yyerror}. This means that an erroneous input line causes the
+calculator program to exit. Now we show how to rectify this deficiency.
The Bison language itself includes the reserved word @code{error}, which
may be included in the grammar rules. In the example below it has
@end group
@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 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 @code{yyerrok}, a
-macro defined automatically by Bison; its meaning is that error recovery is
-complete (@pxref{Error Recovery}). Note the difference between
-@code{yyerrok} and @code{yyerror}; neither one is a misprint.@refill
+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
+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
+@code{yyerrok}, a macro defined automatically by Bison; its meaning is
+that error recovery is complete (@pxref{Error Recovery}). Note the
+difference between @code{yyerrok} and @code{yyerror}; neither one is a
+misprint.@refill
This form of error recovery deals with syntax errors. There are other
kinds of errors; for example, division by zero, which raises an exception
@cindex additional C code section
@cindex C code, section for additional
-The @var{additional C code} section is copied verbatim to the end of
-the parser file, just as the @var{C declarations} section 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. @xref{Interface, ,Parser C-Language Interface}.
+The @var{additional C code} section is copied verbatim to the end of the
+parser file, just as the @var{C declarations} section 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. @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 detects a @dfn{parse error} or @dfn{syntax 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 in Actions}).
+macro @code{YYERROR} (@pxref{Action Features, ,Special Features for Use
+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
@findex YYERROR_VERBOSE
If you define the macro @code{YYERROR_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"}}. It doesn't matter what definition you use for
-@code{YYERROR_VERBOSE}, just whether you define it.
+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"}}. It doesn't matter what
+definition you use for @code{YYERROR_VERBOSE}, just whether you define
+it.
The parser can detect one other kind of error: stack overflow. This
happens when the input contains constructions that are very deeply
@item 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}}.
+function @code{yyerror} is not called. @xref{Parser Function, ,The
+Parser Function @code{yyparse}}.
@item YYACCEPT
Macro to pretend that a complete utterance of the language has been
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