Debugging Your Parser
* Understanding:: Understanding the structure of your parser.
+* Graphviz:: Getting a visual representation of the parser.
+* Xml:: Getting a markup representation of the parser.
* Tracing:: Tracing the execution of your parser.
Tracing Your Parser
* C++ position:: One point in the source file
* C++ location:: Two points in the source file
+* User Defined Location Type:: Required interface for locations
A Complete C++ Example
the current lookahead and the entire stack (except the current
right-hand side symbols) when the parser returns immediately, and
@item
+the current lookahead and the entire stack (including the current right-hand
+side symbols) when the C++ parser (@file{lalr1.cc}) catches an exception in
+@code{parse},
+@item
the start symbol, when the parser succeeds.
@end itemize
Some of the accepted @var{variable}s are:
@itemize @bullet
+@c ================================================== api.location.type
+@item @code{api.location.type}
+@findex %define api.location.type
+
+@itemize @bullet
+@item Language(s): C++, Java
+
+@item Purpose: Define the location type.
+@xref{User Defined Location Type}.
+
+@item Accepted Values: String
+
+@item Default Value: none
+
+@item History: introduced in Bison 2.7
+@end itemize
+
@c ================================================== api.prefix
@item @code{api.prefix}
@findex %define api.prefix
@itemize @bullet
@item Language(s): All
-@item Purpose: Rename exported symbols
+@item Purpose: Rename exported symbols.
@xref{Multiple Parsers, ,Multiple Parsers in the Same Program}.
@item Accepted Values: String
@menu
* Understanding:: Understanding the structure of your parser.
+* Graphviz:: Getting a visual representation of the parser.
+* Xml:: Getting a markup representation of the parser.
* Tracing:: Tracing the execution of your parser.
@end menu
@samp{*}, but also because the
associativity of @samp{/} is not specified.
+Note that Bison may also produce an HTML version of this output, via an XML
+file and XSLT processing (@pxref{Xml}).
+
+@c ================================================= Graphical Representation
+
+@node Graphviz
+@section Visualizing Your Parser
+@cindex dot
+
+As another means to gain better understanding of the shift/reduce
+automaton corresponding to the Bison parser, a DOT file can be generated. Note
+that debugging a real grammar with this is tedious at best, and impractical
+most of the times, because the generated files are huge (the generation of
+a PDF or PNG file from it will take very long, and more often than not it will
+fail due to memory exhaustion). This option was rather designed for beginners,
+to help them understand LR parsers.
+
+This file is generated when the @option{--graph} option is specified
+(@pxref{Invocation, , Invoking Bison}). Its name is made by removing
+@samp{.tab.c} or @samp{.c} from the parser implementation file name, and
+adding @samp{.dot} instead. If the grammar file is @file{foo.y}, the
+Graphviz output file is called @file{foo.dot}.
+
+The following grammar file, @file{rr.y}, will be used in the sequel:
+
+@example
+%%
+@group
+exp: a ";" | b ".";
+a: "0";
+b: "0";
+@end group
+@end example
+
+The graphical output is very similar to the textual one, and as such it is
+easier understood by making direct comparisons between them. See
+@ref{Debugging, , Debugging Your Parser} for a detailled analysis of the
+textual report.
+
+@subheading Graphical Representation of States
+
+The items (pointed rules) for each state are grouped together in graph nodes.
+Their numbering is the same as in the verbose file. See the following points,
+about transitions, for examples
+
+When invoked with @option{--report=lookaheads}, the lookahead tokens, when
+needed, are shown next to the relevant rule between square brackets as a
+comma separated list. This is the case in the figure for the representation of
+reductions, below.
+
+@sp 1
+
+The transitions are represented as directed edges between the current and
+the target states.
+
+@subheading Graphical Representation of Shifts
+
+Shifts are shown as solid arrows, labelled with the lookahead token for that
+shift. The following describes a reduction in the @file{rr.output} file:
+
+@example
+@group
+state 3
+
+ 1 exp: a . ";"
+
+ ";" shift, and go to state 6
+@end group
+@end example
+
+A Graphviz rendering of this portion of the graph could be:
+
+@center @image{figs/example-shift, 100pt}
+
+@subheading Graphical Representation of Reductions
+
+Reductions are shown as solid arrows, leading to a diamond-shaped node
+bearing the number of the reduction rule. The arrow is labelled with the
+appropriate comma separated lookahead tokens. If the reduction is the default
+action for the given state, there is no such label.
+
+This is how reductions are represented in the verbose file @file{rr.output}:
+@example
+state 1
+
+ 3 a: "0" . [";"]
+ 4 b: "0" . ["."]
+
+ "." reduce using rule 4 (b)
+ $default reduce using rule 3 (a)
+@end example
+
+A Graphviz rendering of this portion of the graph could be:
+
+@center @image{figs/example-reduce, 120pt}
+
+When unresolved conflicts are present, because in deterministic parsing
+a single decision can be made, Bison can arbitrarily choose to disable a
+reduction, see @ref{Shift/Reduce, , Shift/Reduce Conflicts}. Discarded actions
+are distinguished by a red filling color on these nodes, just like how they are
+reported between square brackets in the verbose file.
+
+The reduction corresponding to the rule number 0 is the acceptation state. It
+is shown as a blue diamond, labelled "Acc".
+
+@subheading Graphical representation of go tos
+
+The @samp{go to} jump transitions are represented as dotted lines bearing
+the name of the rule being jumped to.
+
+Note that a DOT file may also be produced via an XML file and XSLT
+processing (@pxref{Xml}).
+
+@c ================================================= XML
+
+@node Xml
+@section Visualizing your parser in multiple formats
+@cindex xml
+
+Bison supports two major report formats: textual output
+(@pxref{Understanding}) when invoked with option @option{--verbose}, and DOT
+(@pxref{Graphviz}) when invoked with option @option{--graph}. However,
+another alternative is to output an XML file that may then be, with
+@command{xsltproc}, rendered as either a raw text format equivalent to the
+verbose file, or as an HTML version of the same file, with clickable
+transitions, or even as a DOT. The @file{.output} and DOT files obtained via
+XSLT have no difference whatsoever with those obtained by invoking
+@command{bison} with options @option{--verbose} or @option{--graph}.
+
+The textual file is generated when the options @option{-x} or
+@option{--xml[=FILE]} are specified, see @ref{Invocation,,Invoking Bison}.
+If not specified, its name is made by removing @samp{.tab.c} or @samp{.c}
+from the parser implementation file name, and adding @samp{.xml} instead.
+For instance, if the grammar file is @file{foo.y}, the default XML output
+file is @file{foo.xml}.
+
+Bison ships with a @file{data/xslt} directory, containing XSL Transformation
+files to apply to the XML file. Their names are non-ambiguous:
+
+@table @file
+@item xml2dot.xsl
+Used to output a copy of the DOT visualization of the automaton.
+@item xml2text.xsl
+Used to output a copy of the .output file.
+@item xml2xhtml.xsl
+Used to output an xhtml enhancement of the .output file.
+@end table
+
+Sample usage (requires @code{xsltproc}):
+@example
+$ bison -x input.y
+@group
+$ bison --print-datadir
+/usr/local/share/bison
+@end group
+$ xsltproc /usr/local/share/bison/xslt/xml2xhtml.xsl input.xml > input.html
+@end example
+
+@c ================================================= Tracing
@node Tracing
@section Tracing Your Parser
Description of the grammar, conflicts (resolved and unresolved), and
parser's automaton.
+@item itemset
+Implies @code{state} and augments the description of the automaton with
+the full set of items for each state, instead of its core only.
+
@item lookahead
Implies @code{state} and augments the description of the automaton with
each rule's lookahead set.
-@item itemset
-Implies @code{state} and augments the description of the automaton with
-the full set of items for each state, instead of its core only.
+@item solved
+Implies @code{state}. Explain how conflicts were solved thanks to
+precedence and associativity directives.
+
+@item all
+Enable all the items.
+
+@item none
+Do not generate the report.
@end table
@item --report-file=@var{file}
@table @file
@item position.hh
@itemx location.hh
-The definition of the classes @code{position} and @code{location},
-used for location tracking. @xref{C++ Location Values}.
+The definition of the classes @code{position} and @code{location}, used for
+location tracking. These files are not generated if the @code{%define}
+variable @code{api.location.type} is defined. @xref{C++ Location Values}.
@item stack.hh
An auxiliary class @code{stack} used by the parser.
@c - %define filename_type "const symbol::Symbol"
When the directive @code{%locations} is used, the C++ parser supports
-location tracking, see @ref{Tracking Locations}. Two auxiliary classes
-define a @code{position}, a single point in a file, and a @code{location}, a
-range composed of a pair of @code{position}s (possibly spanning several
-files).
+location tracking, see @ref{Tracking Locations}.
+
+By default, two auxiliary classes define a @code{position}, a single point
+in a file, and a @code{location}, a range composed of a pair of
+@code{position}s (possibly spanning several files). But if the
+@code{%define} variable @code{api.location.type} is defined, then these
+classes will not be generated, and the user defined type will be used.
@tindex uint
In this section @code{uint} is an abbreviation for @code{unsigned int}: in
genuine code only the latter is used.
@menu
-* C++ position:: One point in the source file
-* C++ location:: Two points in the source file
+* C++ position:: One point in the source file
+* C++ location:: Two points in the source file
+* User Defined Location Type:: Required interface for locations
@end menu
@node C++ position
@code{filename} defined, or equal filename/line or column.
@end deftypefun
+@node User Defined Location Type
+@subsubsection User Defined Location Type
+@findex %define api.location.type
+
+Instead of using the built-in types you may use the @code{%define} variable
+@code{api.location.type} to specify your own type:
+
+@example
+%define api.location.type @var{LocationType}
+@end example
+
+The requirements over your @var{LocationType} are:
+@itemize
+@item
+it must be copyable;
+
+@item
+in order to compute the (default) value of @code{@@$} in a reduction, the
+parser basically runs
+@example
+@@$.begin = @@$1.begin;
+@@$.end = @@$@var{N}.end; // The location of last right-hand side symbol.
+@end example
+@noindent
+so there must be copyable @code{begin} and @code{end} members;
+
+@item
+alternatively you may redefine the computation of the default location, in
+which case these members are not required (@pxref{Location Default Action});
+
+@item
+if traces are enabled, then there must exist an @samp{std::ostream&
+ operator<< (std::ostream& o, const @var{LocationType}& s)} function.
+@end itemize
+
+@sp 1
+
+In programs with several C++ parsers, you may also use the @code{%define}
+variable @code{api.location.type} to share a common set of built-in
+definitions for @code{position} and @code{location}. For instance, one
+parser @file{master/parser.yy} might use:
+
+@example
+%defines
+%locations
+%define namespace "master::"
+@end example
+
+@noindent
+to generate the @file{master/position.hh} and @file{master/location.hh}
+files, reused by other parsers as follows:
+
+@example
+%define api.location.type "master::location"
+%code requires @{ #include <master/location.hh> @}
+@end example
+
@node C++ Parser Interface
@subsection C++ Parser Interface
@c - define parser_class_name
@deftypemethod {parser} {int} parse ()
Run the syntactic analysis, and return 0 on success, 1 otherwise.
+
+@cindex exceptions
+The whole function is wrapped in a @code{try}/@code{catch} block, so that
+when an exception is thrown, the @code{%destructor}s are called to release
+the lookahead symbol, and the symbols pushed on the stack.
@end deftypemethod
@deftypemethod {parser} {std::ostream&} debug_stream ()
defines a class representing a @dfn{location}, a range composed of a pair of
positions (possibly spanning several files). The location class is an inner
class of the parser; the name is @code{Location} by default, and may also be
-renamed using @code{%define location_type "@var{class-name}"}.
+renamed using @code{%define api.location.type "@var{class-name}"}.
The location class treats the position as a completely opaque value.
By default, the class name is @code{Position}, but this can be changed
-with @code{%define position_type "@var{class-name}"}. This class must
+with @code{%define api.position.type "@var{class-name}"}. This class must
be supplied by the user.
@deftypemethod {Lexer} {void} yyerror (Location @var{loc}, String @var{msg})
This method is defined by the user to emit an error message. The first
parameter is omitted if location tracking is not active. Its type can be
-changed using @code{%define location_type "@var{class-name}".}
+changed using @code{%define api.location.type "@var{class-name}".}
@end deftypemethod
@deftypemethod {Lexer} {int} yylex ()
@code{yylex} returned, and the first position beyond it. These
methods are not needed unless location tracking is active.
-The return type can be changed using @code{%define position_type
+The return type can be changed using @code{%define api.position.type
"@var{class-name}".}
@end deftypemethod
@xref{Java Scanner Interface}.
@end deffn
-@deffn {Directive} {%define location_type} "@var{class}"
+@deffn {Directive} {%define api.location.type} "@var{class}"
The name of the class used for locations (a range between two
positions). This class is generated as an inner class of the parser
class by @command{bison}. Default is @code{Location}.
+Formerly named @code{location_type}.
@xref{Java Location Values}.
@end deffn
@xref{Java Bison Interface}.
@end deffn
-@deffn {Directive} {%define position_type} "@var{class}"
+@deffn {Directive} {%define api.position.type} "@var{class}"
The name of the class used for positions. This class must be supplied by
the user. Default is @code{Position}.
+Formerly named @code{position_type}.
@xref{Java Location Values}.
@end deffn
@c LocalWords: getLVal defvar deftypefn deftypefnx gotos msgfmt Corbett LALR's
@c LocalWords: subdirectory Solaris nonassociativity perror schemas Malloy ints
@c LocalWords: Scannerless ispell american ChangeLog smallexample CSTYPE CLTYPE
-@c LocalWords: clval CDEBUG cdebug deftypeopx yyterminate
+@c LocalWords: clval CDEBUG cdebug deftypeopx yyterminate LocationType
+@c LocalWords: errorVerbose
@c Local Variables:
@c ispell-dictionary: "american"
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