NAME¶

bisonc++ - Generate a C++ parser class and parsing function

SYNOPSIS¶

bisonc++ [OPTIONS] grammar-file

SECTIONS¶

This manual page contains the following sections:

1. DESCRIPTION

overview and short history of of bisonc++;

2. GENERATED FILES

files bisonc++ may generate;

3. OPTIONS

Bisonc++’s command-line options;

4. DIRECTIVES

Bisonc++’s grammar-specification directives;

5. POLYMORPHIC SEMANTIC VALUES

How to use polymorphic semantic values in parsers generated by bisonc++;

6. PUBLIC MEMBERS AND -TYPES

Members and types that can be used by calling software;

7. PRIVATE ENUMS AND -TYPES

Enumerations and types only available to the Parser class;

8. PRIVATE MEMBER FUNCTIONS

Member functions that are only available to the Parser class;

9. PRIVATE DATA MEMBERS

Data members that are only available to the Parser class;

10. TYPES AND VARIABLES IN THE ANONYMOUS NAMESPACE

An overview of the types and variables that are used to define and store the grammar-tables generated by bisonc++;

11. RESTRICTIONS ON TOKEN NAMES

Name restrictions for user-defined symbols;

12. OBSOLETE SYMBOLS

Symbols available to bison(1), but not to bisonc++;

13. EXAMPLE

Guess what this is?

14. USING PARSER-CLASS SYMBOLS IN LEXICAL SCANNERS

How to refer to Parser tokens from within a lexical scanner;

15. FILES

(Skeleton) files used by bisonc++;

16. SEE ALSO

References to other programs and documentation;

17. BUGS

Some additional stuff that should not qualify as bugs.

18. ABOUT bisonc++

More history;

AUTHOR

At the end of this man-page.

 

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1. DESCRIPTION¶

Bisonc++ derives from previous work on bison by Alain Coetmeur (coetmeur@icdc.fr), who created in the early ’90s a C++ class encapsulating the yyparse function as generated by the GNU-bison parser generator. Initial versions of bisonc++ (up to version 0.92) wrapped Alain’s program in a program offering a more modern user-interface, removing all old-style ( C) %define directives from bison++’s input specification file (see below for an in-depth discussion of the differences between bison++ and bisonc++). Starting with version 0.98, bisonc++ represents a complete rebuilt of the parser generator, closely following descriptions given in Aho, Sethi and Ullman’s Dragon Book. Since version 0.98 bisonc++ is a C++ program, rather than a C program generating C++ code. Bisonc++ expands the concepts initially implemented in bison and bison++, offering a cleaner setup of the generated parser class. The parser class is derived from a base-class, mainly containing the parser’s token- and type-definitions as well as several member functions which should not be modified by the programmer. Most of these base-class members might also be defined directly in the parser class, but were defined in the parser’s base-class. This design results in a very lean parser class, declaring only members that are actually defined by the programmer or that have to be defined by bisonc++ itself (e.g., the member function parse as well as some support functions requiring access to facilities that are only available in the parser class itself, rather than in the parser’s base class). This design does not require the use of virtual members: the members which are not involved in the actual parsing process may always be (re)implemented directly by the programmer. Thus there is no need to apply or define virtual member functions. In fact, there are only two public members in the parser class generated by bisonc++: setDebug (see below) and parse. Remaining members are private, and those that can be redefined by the programmer using bisonc++ usually receive initial, very simple default in-line implementations. The (partial) exception to this rule is the member function lex, producing the next lexical token. For lex either a standardized interface or a mere declaration is offerered (requiring the programmer to provide his/her own lex implementation). To enforce a primitive namespace, bison used a well-known naming-convention: all its public symbols started with yy or YY. Bison++ followed bison in this respect, even though a class by itself offers enough protection of its identifiers. Consequently, these yy and YY conventions are now outdated, and bisonc++ does not generate or use symbols defined in either the parser (base) class or in its member functions starting with yy or YY. Instead, following a suggestion by Lakos (2001), all data members have names starting with d_, and all static data members have names starting with s_. This convention was not introduced to enforce identifier protection, but to clarify the storage type of variables. Other (local) symbols lack specific prefixes. Furthermore, bisonc++ allows its users to define the parser class in a particular namespace of their own choice. Bisonc++ should be used as follows:

o

As usual, a grammar must be defined. Using bisonc++ this is not different, and the reader is referred to bisonc++’s manual and other sources (like Aho, Sethi and Ullman’s book) for details about how to specify and decorate grammars.

o

The number and function of the various %define declarations as used by bison++, however, is greatly modified. Actually, all of bison’s %define declarations were replaced by their (former) first arguments. Furthermore, `macro-style’ declarations are no longer supported or required. Finally, all directives use lower-case characters only and do not contain underscore characters (but sometimes hyphens). E.g., %define DEBUG is now declared as %debug; %define LSP_NEEDED is now declared as %lsp-needed (note the hyphen).

o

As noted, no `macro style’ %define declarations are required anymore. Instead, the normal practice of defining class members in source files and declaring them in a class header files can be adhered to using bisonc++. Basically, bisonc++ concentrates on its main tasks: the definition of an parser class and the implementation of its parsing function int parse, leaving all other parts of the parser class’ definition to the programmer.

o

Having specified the grammar and (usually) some directives bisonc++ is able to generate files defining the parser class and the implementation of the member function parse and its support functions. See the next section for details about the various files that may be generated by bisonc++.

o

All members (except for the member parse) and its support functions must be implemented by the programmer. Additional member functions should be declared in the parser class’ header. At the very least the member int lex() must be implemented (although a standardized implementation can also be generated by bisonc++). The member lex is called by parse to obtain the next available token. The member function void error(char const *msg) may also be re-implemented by the programmer, but a basic in-line implementation is provided by default. The member function error is called when parse detects (syntactic) errors.

o

The parser can now be used in a program. A very simple example would be:

    int main()
    {
        Parser parser;
        return parser.parse();
    }
        
    

 

2. GENERATED FILES¶

Bisonc++ may create the following files:

o

A file containing the implementation of the member function parse and its support functions. The member parse is a public member that can be called to parse a token-sequence according to a specified LALR1 type of grammar. The implementations of these members is by default written on the file parse.cc. The programmer should not modify the contents of this file; by default it is rewritten every time bisonc++ is called.

o

A file containing an initial setup of the parser class, containing the declaration of the public member parse and of its (private) support members. New members may safely be declared in the parser class, as it is only created by bisonc++ if not yet existing, using the filename <parser-class>.h (where <parser-class> is the the name of the defined parser class).

o

A file containing the parser class’ base class. This base class should not be modified by the programmer. It contains types defined by bisonc++, as well as several (protected) data members and member functions, which should not be redefined by the programmer. All symbolic parser terminal tokens are defined in this class, thereby escalating these definitions in a separate class (cf. Lakos, (2001)), which in turn prevents circular dependencies between the lexical scanner and the parser (circular dependencies may easily occur here, as the parser needs access to the lexical scanner class when defining the lexical scanner as one of its data members, whereas the lexical scanner needs access to the parser class to know about the grammar’s symbolic terminal tokens; escalation is a way out of such circular dependencies). By default this file is (re)written any time bisonc++ is called, using the filename <parser-class>base.h.

o

A file containing an implementation header. The implementation header rather than the parser’s class header file should be included by the parser’s source files implementing member functions declared by the programmer. The implementation header first includes the parser class’s header file, and then provides default in-line implementations for its members error and print (which may be altered by the programmer). The member lex may also receive a standard in-line implementation. Alternatively, its implementation can be provided by the programmer (see below). Any directives and/or namespace directives required for the proper compilation of the parser’s additional member functions should be declared next. The implementation header is included by the file defining parse. By default the implementation header is created if not yet existing, receiving the filename <parser-class>.ih.

o

A verbose description of the generated parser. This file is comparable to the verbose ouput file originally generated by bison++. It is generated when the option --verbose or -V is provided. If so, bisonc++ writes the file <grammar>.output, where <grammar> is the name of the file containing the grammar definition.

 

3. OPTIONS¶

If available, single letter options are listed between parentheses following their associated long-option variants. Single letter options require arguments if their associated long options require arguments as well. Options affecting the class header or implementation header file are ignored if these files already exist.

o

--analyze-only (-A)

 

Only analyze the grammar. No files are (re)written. This option can be used to test the grammatic correctness of modification `in situ’, without overwriting previously generated files. If the grammar contains syntactic errors only syntax analysis is performed.

o

--baseclass-header=header (-b)

 

Use header as the pathname of the file to contain the parser’s base class. This class defines, e.g., the parser’s symbolic tokens. Defaults to the name of the parser class plus the suffix base.h. It is generated, unless otherwise indicated (see --no-baseclass-header and --dont-rewrite-baseclass-header below).

o

--baseclass-preinclude=header (-H)

 

Use header as the pathname to the file preincluded in the parser’s base-class header. This option is needed in situations where the base class header file refers to types which might not yet be known. E.g., with %polymorphic a std::string value type might be used. Since the string header file is not by default included in parserbase.h we need a way to inform the compiler about this and possibly other headers. The suggested procedure is to use a pre-include header file declaring the required types. By default ` header’ is surrounded by double quotes: #include "header" is used when the option -H header is specified. When the argument is surrounded by pointed brackets #include <header> is included. In the latter case, quotes might be required to escape interpretation by the shell (e.g., using -H ’<header>’).

o

--baseclass-skeleton=skeleton (-B)

 

Use skeleton as the pathname of the file containing the skeleton of the parser’s base class. Its filename defaults to bisonc++base.h.

o

--class-header=header (-c)

 

Use header as the pathname of the file to contain the parser class. Defaults to the name of the parser class plus the suffix .h

o

--class-name className

 

Defines the name of the C++ class that is generated. If neither this option, nor the %class-name directory is specified, then the default class name ( Parser) is used.

o

--class-skeleton=skeleton (-C)

 

Use skeleton as the pathname of the file containing the skeleton of the parser class. Its filename defaults to bisonc++.h.

o

--construction

 

Details about the construction of the parsing tables are written to the same file as written by the --verbose option (i.e., <grammar>.output, where <grammar> is the input file read by bisonc++. This information is primarily useful for developers. It augments the information written to the verbose grammar output file, generated by the --verbose option.

o

--debug

 

Provide parse and its support functions with debugging code, showing the actual parsing process on the standard output stream. When included, the debugging output is active by default, but its activity may be controlled using the setDebug(bool on-off) member. An #ifdef DEBUG macro is not supported by bisonc++. Rerun bisonc++ without the --debug option to remove the debugging code.

o

--error-verbose

 

When a syntactic error is reported, the generated parse function will dump the parser’s state stack to the standard output stream. The stack dump shows on separate lines a stack index followed by the state stored at the indicated stack element. The first stack element is the stack’s top element.

o

--filenames=filename (-f)

 

Specify a filename to use for all files produced by bisonc++. Specific options overriding particular filenames are also available (which then, in turn, overide the name specified by this option).

o

--flex

 

Bisonc++ generates code calling d_scanner.yylex() to obtain the next lexical token, and calling d_scanner.YYText() for the matched text, unless overruled by options or directives explicitly defining these functions. By default, the interface defined by flexc++(1) is used. This option is only interpreted if the --scanner option or %scanner directive is also used.

o

--force-class-header

 

By default the generated class header is not overwritten once it has been created. This option can be used to force the (re)writing of the file containing the parser’s class.

o

--force-implementation-header

 

By default the generated implementation header is not overwritten once it has been created. This option can be used to force the (re)writing of the implementation header file.

o

--help (-h)

 

Write basic usage information to the standard output stream and terminate.

o

--implementation-header=header (-i)

 

Use header as the pathname of the file to contain the implementation header. Defaults to the name of the generated parser class plus the suffix .ih. The implementation header should contain all directives and declarations only used by the implementations of the parser’s member functions. It is the only header file that is included by the source file containing parse’s implementation . User defined implementation of other class members may use the same convention, thus concentrating all directives and declarations that are required for the compilation of other source files belonging to the parser class in one header file.

o

--implementation-skeleton=skeleton (-I)

 

Use skeleton as the pathname of the file containing the skeleton of the implementation header. Its filename defaults to bisonc++.ih.

o

--insert-stype

 

This option is only effective if the debug option (or %debug directive) has also been specified. When insert-stype has been specified the parsing function’s debug output will also show selected semantic values. It should only be used if objects or variables of the semantic value type STYPE__ can be inserted into ostreams.

o

--max-inclusion-depth=value

 

Set the maximum number of nested grammar files. Defaults to 10.

o

--namespace=namespace (-n)

 

Define the parser base class, the paser class and the parser implentations in the namespace namespace. By default no namespace is defined. If this options is used the implementation header will contain a commented out using namespace declaration for the requested namespace.

o

--no-baseclass-header

 

Do not write the file containing the parser class’ base class, even if that file doesn’t yet exist. By default the file containing the parser’s base class is (re)written each time bisonc++ is called. Note that this option should normally be avoided, as the base class defines the symbolic terminal tokens that are returned by the lexical scanner. By suppressing the construction of this file any modification in these terminal tokens will not be communicated to the lexical scanner.

o

--no-lines

 

Do not put #line preprocessor directives in the file containing the parser’s parse function. By default #line preprocessor directives are placed in the file containing the parser’s parse function. This option allows the compiler and debuggers to associate errors with lines in your grammar specification file, rather than with the source file containing the parse function itself.

o

--no-parse-member

 

Do not write the file containing the parser’s predefined parser member functions, even if that file doesn’t yet exist. By default the file containing the parser’s parse member function is (re)written each time bisonc++ is called. Note that this option should normally be avoided, as this file contains parsing tables which are altered whenever the grammar definition is modified.

o

--own-debug

 

Extensively displays the actions performed by bisonc++’s parser when it processes the grammar specification s. This implies the --verbose option.

o

--own-tokens (-T)

 

The tokens returned as well as the text matched when bisonc++ reads its input files(s) are shown when this option is used.

This option does not result in the generated parsing function displaying returned tokens and matched text. If that is what you want, use the --print-tokens option.

o

--parsefun-skeleton=skeleton (-P)

 

Use skeleton as the pathname of the file containing the parsing member function’s skeleton. Its filename defaults to bisonc++.cc.

o

--parsefun-source=source (-p)

 

Define source as the name of the source file to contain the parser member function parse. Defaults to parse.cc.

o

--polymorphic-skeleton=skeleton (-M)

 

Use skeleton as the pathname of the file containing the skeleton of the polymorphic template classes. Its filename defaults to bisonc++polymorphic.

o

--polymorphic-inline-skeleton=skeleton (-m)

 

Use skeleton as the pathname of the file containing the skeleton of the inline implementations of the members of the polymorphic template classes. Its filename defaults to bisonc++polymorphic.

o

--print-tokens (-t)

 

The generated parsing function implements a function print__ displaying (on the standard output stream) the tokens returned by the parser’s scanner as well as the corresponding matched text. This implementation is suppressed when the parsing function is generated without using this option. The member print__) is called from Parser::print, which is defined in-line in the the parser’s class header. Calling Parser::print__, therefore, can also easily be controlled by an option controlled by the program using the parser generated by bisonc++.

This option does not show the tokens returned and text matched by bisonc++ itself when reading its input s. If that is what you want, use the --own-tokens option.

o

--required-tokens=number

 

Following a syntactic error, require at least number successfully processed tokens before another syntactic error can be reported. By default number is zero.

o

--scanner=header (-s)

 

Use header as the pathname to the file defining a class Scanner. When this option is used the parser’s member int lex() is predefined as

    int lex()
    {
        return d_scanner.lex();
    }
                
    

and an object Scanner d_scanner is composed into the parser. The example shows the function that’s called by default. By specifying the --flex option (or %flex directive) the function d_scanner.yylex() is called. Any other function to call can be specified using the --scanner-token-function option (or %scanner-token-function directive).

By default header is surrounded by double quotes (using, e.g., #include "header"). When the argument is surrounded by pointed brackets #include <header> is included.

o

--scanner-debug

 

Show de scanner’s matched rules and returned tokens. This offers an extensive display of the rules and tokens matched and returned by bisonc++’s scanner, not of just the tokens and matched text received by bisonc++. If that is what you want use the --own-tokens option.

o

--scanner-matched-text-function=function-call

 

The scanner function returning the text that was matched at the last call of the scanner’s token function. A complete function call expression should be provided (including a scanner object, if used). This option overrules the d_scanner.matched() call used by default when the %scanner directive is specified, and it overrules the d_scanner.YYText() call used when the %flex directive is provided. Example:

    --scanner-matched-text-function "myScanner.matchedText()"
                
    

 

o

--scanner-token-function=function-call

 

The scanner function returning the next token, called from the parser’s lex function. A complete function call expression should be provided (including a scanner object, if used). This option overrules the d_scanner.lex() call used by default when the %scanner directive is specified, and it overrules the d_scanner.yylex() call used when the %flex directive is provided. Example:

    --scanner-token-function "myScanner.nextToken()"
                
    

 

o

--show-filenames

 

Writes the names of the generated files to the standard error stream.

o

--skeleton-directory=directory (-S)

 

Specifies the directory containing the skeleton files to use. This option can be overridden by the specific skeleton-specifying options ( -B -C, -H, -I, -M and -m).

o

--target-directory=directory

 

Specifies the directory where generated files should be written. By default this is the directory of bisonc++’s input file. The --target-directory option does not affect files that were explicitly named (either as option or as directive).

o

--thread-safe

 

No static data are modified, making bisonc++ thread-safe.

o

--usage

 

Write basic usage information to the standard output stream and terminate.

o

--verbose (-V)

 

Write a file containing verbose descriptions of the parser states and what is done for each type of look-ahead token in that state. This file also describes all conflicts detected in the grammar, both those resolved by operator precedence and those that remain unresolved. It is not created by default, but if requested the information is written on <grammar>.output, where <grammar> is the grammar specification file passed to bisonc++.

o

--version (-v)

 

Display bisonc++’s version number and terminate.

 

4. DIRECTIVES¶

The following directives can be specified in the initial section of the grammar specification file. When command-line options for directives exist, they overrule the corresponding directives given in the grammar specification file. Directives affecting the class header or implementation header file are ignored if these files already exist.

o

%baseclass-header header

 

Defines the pathname of the file containing the parser’s base class. This directive is overridden by the --baseclass-header or -b command-line options.

o

%baseclass-preinclude header

 

Use header as the pathname to the file pre-included in the parser’s base-class header. See the description of the --baseclass-preinclude option for details about this directive. Like the convention adopted for this argument, header will (by default) be surrounded by double quotes. However, when the argument is surrounded by pointed brackets #include <header> is included.

o

%class-header header

 

Defines the pathname of the file containing the parser class. This directive is overridden by the --class-header or -c command-line options.

o

%class-name parser-class-name

 

Declares the name of the parser class. It defines the name of the C++ class that is generated. If no %class-name is specified the default class name Parser is used.

o

%debug

 

Provide parse and its support functions with debugging code, showing the actual parsing process on the standard output stream. When included, the debugging output is active by default, but its activity may be controlled using the setDebug(bool on-off) member. No #ifdef DEBUG macros are used anymore. By rerunning bisonc++ without the --debug option or %debug declaration an equivalent parser is generated not containing the debugging code.

o

%error-verbose

 

This directive can be specified to dump the parser’s state stack to the standard output stream when the parser encounters a syntactic error. The stack dump shows on separate lines a stack index followed by the state stored at the indicated stack element. The first stack element is the stack’s top element.

o

%expect number

 

This directive specifies the exact number of shift/reduce and reduce/reduce conflicts for which no warnings are to be generated. Details of the conflicts are reported in the verbose output file (e.g., grammar.output). If the number of encountered conflicts deviates from ` number’, then this directive is ignored.

o

%filenames header

 

Defines the generic name of all generated files, unless overridden by specific names. This directive is overridden by the --filenames or -f command-line options.

o

%flex

 

When provided, the scanner matched text function is called as d_scanner.YYText(), and the scanner token function is called as d_scanner.yylex(). This directive is only interpreted if the %scanner directive is also provided.

o

%implementation-header header

 

Defines the pathname of the file containing the implementation header. This directive is overridden by the --implementation-header or -i command-line options.

o

%include path

 

This directive is used to switch to path while processing the grammar description. Unless path is an absolute file-path, path is searched relative to the location of bisonc++’s grammar specification file. This directive can be used to split long grammar specification files in shorter, meaningful units. After processing path processing continues beyond the %include path directive.

o

%left terminal ...

 

Defines the names of symbolic terminal tokens that must be treated as left-associative. I.e., in case of a shift/reduce conflict, a reduction is preferred over a shift. Sequences of %left, %nonassoc, %right and %token directives may be used to define the precedence of operators. In expressions, the first used directive will have the lowest precedence, the last used the highest. See also %token below.

o

%locationstruct struct-definition

 

Defines the organization of the location-struct data type LTYPE__. This struct should be specified analogously to the way the parser’s stacktype is defined using %union (see below). The location struct is named LTYPE__. If neither locationstruct nor LTYPE__ is specified, the aforementioned default struct is used.

o

%lsp-needed

 

Defining this causes bisonc++ to include code into the generated parser using the standard location stack. The token-location type defaults to the following struct, defined in the parser’s base class when this directive is specified:

    struct LTYPE__
    {
        int timestamp;
        int first_line;
        int first_column;
        int last_line;
        int last_column;
        char *text;
    };
           
    

Bisonc++ does not provide the elements of the LTYPE__ struct with values. Action blocks of production rules may refer to the location stack element associated with a production element using @ variables, like @1.timestamp, @3.text, @5. The rule’s location struct itself may be referred to as either d_loc__ or @@.

o

%ltype typename

 

Specifies a user-defined token location type. If %ltype is used, typename should be the name of an alternate (predefined) type (e.g., size_t). It should not be used if a %locationstruct specification is defined (see below). Within the parser class, this type is available as the type ` LTYPE__’. All text on the line following %ltype is used for the typename specification. It should therefore not contain comment or any other characters that are not part of the actual type definition.

o

%namespace namespace

 

Define all of the code generated by bisonc++ in the name space namespace. By default no name space is defined. If this options is used the implementation header is provided with a commented out using namespace declaration for the specified name space. This directive is overridden by the --namespace command-line option.

o

%negative-dollar-indices

 

Do not generate warnings when zero- or negative dollar-indices are used in the grammar’s action blocks. Zero or negative dollar-indices are commonly used to implement inherited attributes, and should normally be avoided. When used, they can be specified like $-1 or $<type>-1, where type is empty, an STYPE__ tag or a field-name.

o

%no-lines

 

By default #line preprocessor directives are inserted just before action statements in the file containing the parser’s parse function. These directives are suppressed by the %no-lines directive.

o

%nonassoc terminal ...

 

Defines the names of symbolic terminal tokens that should be treated as non-associative. I.e., in case of a shift/reduce conflict, a reduction is preferred over a shift. Sequences of %left, %nonassoc, %right and %token directives may be used to define the precedence of operators. In expressions, the first used directive has the lowest precedence, the last one used the highest. See also %token below.

o

%parsefun-source source

 

Defines the pathname of the file containing the parser member parse. This directive is overridden by the --parse-source or -p command-line options.

o

%polymorphic polymorphic-specification(s)

 

Bison’s traditional way of handling multiple semantic values is to use a %union specification (see below). Although %union is also supported by bisonc++, a polymorphic semantic value class is preferred due to its improved type safety.

The %polymorphic directive defines a polymorphic semantic value class and can be used instead of a %union specification. Refer to section POLYMORPHIC SEMANTIC VALUES below or to bisonc++’s user manual for a detailed description of the specification, characteristics, and use of polymorphic semantic values.

o

%prec token

 

Overrules the defined precendence of an operator for a particular grammatical rule. A well known application of %prec is:

    expression:
        ’-’ expression %prec UMINUS
        {
            ...
        }
                
    

Here, the default priority and precedence of the ` -’ token as the subtraction operator is overruled by the precedence and priority of the UMINUS token, which is commonly defined as

    %right UMINUS
                
    

(see below) following, e.g., the ’*’ and ’/’ operators.

o

%print-tokens

 

The print directive provides an implementation of the Parser class’s print__ function displaying the current token value and the text matched by the lexical scanner as received by the generated parse function.

o

%required-tokens number

 

Following a syntactic error, require at least number successfully processed tokens before another syntactic error can be reported. By default number is zero.

o

%right terminal ...

 

Defines the names of symbolic terminal tokens that should be treated as right-associative. I.e., in case of a shift/reduce conflict, a shift is preferred over a reduction. Sequences of %left, %nonassoc, %right and %token directives may be used to define the precedence of operators. In expressions, the first used directive will have the lowest precedence, the last used the highest. See also %token below.

o

%scanner header

 

Use header as the pathname to the file pre-included in the parser’s class header. See the description of the --scanner option for details about this option. Similar to the convention adopted for this argument, header by default is surrounded by double quotes. However, when the argument is surrounded by pointed brackets #include <header> is included. This directive results in the definition of a composed Scanner d_scanner data member into the generated parser, and in the definition of a int lex() member, returning d_scanner.lex().

By specifying the %flex directive the function d_scanner.yylex() is called. Any other function to call can be specified using the --scanner-token-function option (or %scanner-token-function directive).

o

%scanner-matched-text-function function-call

 

The scanner function returning the text that was matched by the lexical scanner after its token function (see below) has returned. A complete function call expression should be provided (including a scanner object, if used). Example:

    %scanner-matched-text-function myScanner.matchedText()
                
    

By specifying the %flex directive the function d_scanner.YYText() is called.

If the function call contains white space scanner-token-function should be surrounded by double quotes.

o

%scanner-token-function function-call

 

The scanner function returning the next token, called from the generated parser’s lex function. A complete function call expression should be provided (including a scanner object, if used). Example:

    %scanner-token-function d_scanner.lex()
                
    

If the function call contains white space scanner-token-function should be surrounded by double quotes.

o

%start non-terminal

 

The non-terminal non-terminal should be used as the grammar’s start-symbol. If omitted, the first grammatical rule is used as the grammar’s starting rule. All syntactically correct sentences must be derivable from this starting rule.

o

%stype typename

 

The type of the semantic value of non-terminal tokens. By default it is int. %stype, %union, and %polymorphic are mutually exclusive directives.

Within the parser class, the semantic value type is available by the type name ` STYPE__’. All text on the line following %stype is used for the typename specification. It should therefore not contain comment or any other characters that are not part of the actual type definition.

o

%target-directory directory

 

Specifies the directory where generated files should be written. By default this is the directory of bisonc++’s input file. The %target-directory directive does not affect files that were explicitly named (either as option or as directive).

o

%token terminal ...

 

Defines the names of symbolic terminal tokens. Sequences of %left, %nonassoc, %right and %token directives may be used to define the precedence of operators. In expressions, the first used directive has the lowest precedence, the last used the highest.

 

NOTE: Symbolic tokens are defined as enum-values in the parser’s base class. The names of symbolic tokens may not be equal to the names of the members and types defined by bisonc++ itself (see the next sections). This requirement is not currently enforced by bisonc++, but compilation errors may result if this requirement is violated.

o

%type <type> non-terminal ...

 

In combination with %polymorphic or %union: associate the semantic value of a non-terminal symbol with a polymorphic semantic value tag or union field defined by these directives.

o

%union union-definition

 

Acts identically to the identically named bison and bison++ declaration. Bisonc++ generates a union, named STYPE__, as its semantic type.

o

%weak-tags

 

This directive is ignored unless the %polymorphic directive was specified. It results in the declaration of enum Tag__ rather than enum class Tag__. When in doubt, this directive should not be used.

 

5. POLYMORPHIC SEMANTIC VALUES¶

The %polymorphic directive results in bisonc++ generating a parser using polymorphic semantic values. The various semantic values are specified by pairs, consisting of tags, which are C++ identifiers, and C++ type names. Tags and type names are separated from each other by colons. Multiple tag and type name combinations are separated from each other by semicolons, and an optional semicolon ends the final tag/type specification. Here is an example, defining three semantic values: an int, a std::string and a std::vector<double>:

    %polymorphic INT: int; STRING: std::string; 
                 VECT: std::vector<double>
        

The identifier to the left of the colon is called the tag-identifier (or simply tag), and the type name to the right of the colon is called the type-name. The type-names must be built-in types or must offer default constructors. If type-names refer to types declared in header files that were not already included by the parser’s base class header, then these header s must be inserted using the %baseclass-preinclude directive. The %type directive is used to associate (non-)terminals with semantic value types. Semantic values may also be associated with terminal tokens. In that case it is the lexical scanner’s responsibility to assign a properly typed value to the parser’s STYPE__ d_val__ data member. Non-terminals may be automatically be associated with polymorphic semantic values using %type directives. E.g., following

    %polymorphic INT: int; TEXT: std::string
    %type <INT> expr
        

the expr non-terminal returns int semantic values. In this case, a rule like

    expr:
        expr ’+’ expr
        {
            $$ = $1 + $3;
        }
        

automatically associates $$, $1 and $3 with int values. $$ is an lvalue (representing the semantic value associated with the expr: rule), while $1 and $3 represent the int semantic value associated with the expr non-terminal in the production rule ’-’ expr (rvalues). When negative dollar indices (like $-1) are used, any pre-defined associations between non-terminals and semantic types are ignored. However, semantic value types can explicitly be specified (or provided %type associations can be overruled) using the common `$<type>$’ or `$<type>1’ syntax (in this and following examples index number 1 represents any valid positive index (i.e., not exceeding the number of production rule elements seen so far); -1 represents any valid negative index). The type-overruling syntax does not allow blanks to be used (so $<INT>$ is OK, $< INT >$ isn’t). Various combinations of type-associations and type specifications may be encountered:

o

$-1: %type associations are ignored, and the semantic value type STYPE__ is used instead. A warning is issued unless the %negative-dollar-indices directive was specified.

o

$<tag>-1: error: <tag> specifications are not allowed for negative dollar indices.

 

%type<TAG> and $$ or $1 specifications:

$$ or $1 specifications
%type<TAG>
absent		no <tag>		STYPE__ is used
			$<id>
			$<>
			$<STYPE__>
STYPE__		no <tag>		STYPE__ is used
			$<id>
			$<>
			$<STYPE__>
(existing) tag		no <tag>		auto-tag
			$<id>
			$<>
			$<STYPE__>
(undefined) tag		no <tag>		tag-error
			$<id>
			$<>
			$<STYPE__>

auto-tag: $$ and $1 represent, respectively, $$.get<tag>() and $1.get<tag>(); tag-error: error: tag undefined; tag-override: if id is a defined tag, then $<tag>$ and $<tag>1 represent the tag’s type. Otherwise: error (using undefined tag id). Member calls (`$$.’, `$1.’): When using `$$.’ or `$1.’ default tags are ignored. Instead, a warning is issued that the default tag is ignored. This syntax allows members of the semantic value type ( STYPE__) to be called explicitly. The default tag is only ignored if there are no additional characters (e.g., blanks, closing parentheses) between the dollar-expressions and the member selector operator. The opposite, ignoring default tag associations, is accomplished using tconstructions like $<STYPE__>$ and $<STYPE__>1. The %polymorphic directive adds the following definitions and declarations to the generated base class header and parser source file (if the %namespace directive was used then all declared/defined elements are placed within the name space specified by that directive):

o

Three additional headers are included by the parser’s base class header:

    #include <memory>
    #include <stdexcept>
    #include <type_traits>
            
    

o

All semantic value type identifiers are collected in a strongy typed enumeration ` Tag__’. E.g.,

    enum class Tag__
    {
        INT,
        STRING,
        VECT
    };
        
    

o

The namespace Meta__ contains almost all of the code implementing polymorphic values.

 

The name space Meta__ contains the following elements:

o

A polymorphic base class Base. This class is normally not explicitly referred to by user-defined code. Refer to by bisonc++’s user manual for a detailed description of this class.

o

For each of the tag-identifiers specified with the %polymorphic directive a class template Semantic<Tag__> is defined, containing a data element of the type-name matching the Tag__ for which Semantic<Tag__> was derived. The Semantic<Tag__> classes are normally not explicitly referred to by user-defined code. Refer to by bisonc++’s user manual for a detailed description of these classes.

o

A class SType, derived from std::shared_ptr<Base>. This class becomes the parser’s semantic value type. It offers the following members:

 

Constructors: default, copy and move constructors;

 

Assignment operators: copy and move assignment operators declaring SType or any of the %polymorphic type-names as their right-hand side operands;

 

Tag__ tag() const, returning Semantic<Tag__>’s Tag__ value;

 

ReturnType get<Tag__>() const. ReturnType refers to the semantic value stored inside Semantic<Tag__>. If the type-name is a built-in type a copy of the value is returned, otherwise a reference to a constant object is returned;

 

This member checks for 0-pointers and for Tag__ mismatches between the requested and actual Tag__, throwing a std::logic_error if found. DataType &get<Tag__>() returns a reference to the (modifiable) semantic value stored inside Semantic<Tag__>.

 

This member checks for 0-pointers and for Tag__ mismatches between the requested and actual Tag__, in that case replacing the current Semantic object pointed to by a new Semantic<Tag__> object of the requested Tag__. ReturnType data<Tag__>() const. ReturnType refers to the semantic value stored inside Semantic<Tag__>. If the type-name is a built-in type a copy of the value is returned, otherwise a reference to a constant object is returned;

 

This is a (partially) unchecking variant of the corresponing get member, resulting in a Segfault if used when the shared_ptr holds a 0-pointer, and throwing a std::bad_cast in case of a mismatch between the requested and actual Tag__. DataType &data<Tag__>() returns a reference to the (modifiable) semantic value stored inside Semantic<Tag__>.

 

This is a (partially) unchecking variant of the corresponing get member, resulting in a Segfault if used when the shared_ptr holds a 0-pointer, and throwing a std::bad_cast in case of a mismatch between the requested and actual Tag__. Since bisonc++ declares typedef Meta__::SType STYPE__, polymorphic semantic values can be used without referring to the name space Meta__.

6. PUBLIC MEMBERS AND -TYPES¶

The following public members and types are available to by users of the parser classes generated by bisonc++ (parser class-name prefixes (e.g., Parser::) prefixes are silently implied):

o

LTYPE__:

 

The parser’s location type (user-definable). Available only when either %lsp-needed, %ltype or %locationstruct has been declared.

o

STYPE__:

 

The parser’s stack-type (user-definable), defaults to int.

o

Tokens__:

 

The enumeration type of all the symbolic tokens defined in the grammar file (i.e., bisonc++’s input file). The scanner should be prepared to return these symbolic tokens Note that, since the symbolic tokens are defined in the parser’s class and not in the scanner’s class, the lexical scanner must prefix the parser’s class name to the symbolic token names when they are returned. E.g., return Parser::IDENT should be used rather than return IDENT.

o

int parse():

 

The parser’s parsing member function. It returns 0 when parsing has completed successfully, 1 if errors were encountered while parsing the input.

o

void setDebug(bool mode):

 

This member can be used to activate or deactivate the debug-code compiled into the parsing function. It is always available but is only operational if the %debug directive or --debug option was specified.When debugging code has been compiled into the parsing function, it is not active by default. To activate the debugging code, use setDebug(true). This member can be used to activate or deactivate the debug-code compiled into the parsing function. It is available but has no effect if no debug code has been compiled into the parsing function. When debugging code has been compiled into the parsing function, it is active by default, but debug-code is suppressed by calling setDebug(false).

 

When the %polymorphic directive is used:

o

Meta__:

 

Templates and classes that are required for implementing the polymorphic semantic values are all declared in the Meta__ namespace. The Meta__ namespace itself is nested under the namespace that may have been declared by the %namespace directive.

o

Tag__:

 

The (strongly typed) enum class Tag__ contains all the tag-identifiers specified by the %polymorphic directive. It is declared outside of the Parser’s class, but within the namespace that may have been declared by the %namespace directive.

 

7. PRIVATE ENUMS AND -TYPES¶

The following enumerations and types can be used by members of parser classes generated by bisonc++. They are actually protected members inherited from the parser’s base class.

o

Base::ErrorRecovery__:

 

This enumeration defines two values:

    DEFAULT_RECOVERY_MODE__,
    UNEXPECTED_TOKEN__
        
    

The DEFAULT_RECOVERY_MODE__ terminates the parsing process. The non-default recovery procedure is available once an error token is used in a production rule. When the parsing process throws UNEXPECTED_TOKEN__ the recovery procedure is started (i.e., it is started whenever a syntactic error is encountered or ERROR() is called).

The recovery procedure consists of (1) looking for the first state on the state-stack having an error-production, followed by (2) handling all state transitions that are possible without retrieving a terminal token. Then, in the state requiring a terminal token and starting with the initial unexpected token (3) all subsequent terminal tokens are ignored until a token is retrieved which is a continuation token in that state.

If the error recovery procedure fails (i.e., if no acceptable token is ever encountered) error recovery falls back to the default recovery mode (i.e., the parsing process is terminated).

o

Base::Return__:

 

This enumeration defines two values:

    PARSE_ACCEPT = 0,
    PARSE_ABORT = 1
        
    

(which are of course the parse function’s return values).

 

8. PRIVATE MEMBER FUNCTIONS¶

The following members can be used by members of parser classes generated by bisonc++. When prefixed by Base:: they are actually protected members inherited from the parser’s base class. Members for which the phrase ``Used internally’’ is used should not be called by user-defined code.

o

Base::ParserBase():

 

The default base-class constructor. Used internally.

o

void Base::ABORT() const throw(Return__):

 

This member can be called from any member function (called from any of the parser’s action blocks) to indicate a failure while parsing thus terminating the parsing function with an error value 1. Note that this offers a marked extension and improvement of the macro YYABORT defined by bison++ in that YYABORT could not be called from outside of the parsing member function.

o

void Base::ACCEPT() const throw(Return__):

 

This member can be called from any member function (called from any of the parser’s action blocks) to indicate successful parsing and thus terminating the parsing function. Note that this offers a marked extension and improvement of the macro YYACCEPT defined by bison++ in that YYACCEPT could not be called from outside of the parsing member function.

o

void Base::clearin():

 

This member replaces bison(++)’s macro yyclearin and causes bisonc++ to request another token from its lex() member, even if the current token has not yet been processed. It is a useful member when the parser should be reset to its initial state, e.g., between successive calls of parse. In this situation the scanner will probably be reloaded with new information too (in the context of a flex-generated scanner by, e.g., calling the scanner’s yyrestart member.

o

bool Base::debug() const:

 

This member returns the current value of the debug variable.

o

void Base::ERROR() const throw(ErrorRecovery__):

 

This member can be called from any member function (called from any of the parser’s action blocks) to generate an error, and thus initiate the parser’s error recovery code. Note that this offers a marked extension and improvement of the macro YYERROR defined by bison++ in that YYERROR could not be called from outside of the parsing member function.

o

void error(char const *msg):

 

By default implemented inline in the parser.ih internal header file, it writes a simple message to the standard error stream. It is called when a syntactic error is encountered, and its default implementation may safely be altered.

o

void errorRecovery__():

 

Used internally.

o

void Base::errorVerbose__():

 

Used internally.

o

void executeAction(int):

 

Used internally.

o

int lex():

 

By default implemented inline in the parser.ih internal header file, it can be pre-implemented by bisonc++ using the scanner option or directive (see above); alternatively it must be implemented by the programmer. It interfaces to the lexical scanner, and should return the next token produced by the lexical scanner, either as a plain character or as one of the symbolic tokens defined in the Parser::Tokens__ enumeration. Zero or negative token values are interpreted as `end of input’.

o

int lookup(bool):

 

Used internally.

o

void nextToken():

 

Used internally.

o

void Base::pop__():

 

Used internally.

o

void Base::popToken__():

 

Used internally.

o

void print__()():

 

Used internally.

o

void print()):

 

By default implemented inline in the parser.ih internal header file, this member calls print__ to display the last received token and corrseponding matched text. The print__ member is only implemented if the --print-tokens option or %print-tokens directive was used when the parsing function was generated. Calling print__ from print is unconditional, but can easily be controlled by the using program, by defining, e.g., a command-line option.

o

void Base::push__():

 

Used internally.

o

void Base::pushToken__():

 

Used internally.

o

void Base::reduce__():

 

Used internally.

o

void Base::symbol__():

 

Used internally.

o

void Base::top__():

 

Used internally.

 

9. PRIVATE DATA MEMBERS¶

The following data members can be used by members of parser classes generated by bisonc++. All data members are actually protected members inherited from the parser’s base class.

o

size_t d_acceptedTokens__:

 

Counts the number of accepted tokens since the start of the parse() function or since the last detected syntactic error. It is initialized to d_requiredTokens__ to allow an early error to be detected as well.

o

bool d_debug__:

 

When the debug option has been specified, this variable (true by default) determines whether debug information is actually displayed.

o

LTYPE__ d_loc__:

 

The location type value associated with a terminal token. It can be used by, e.g., lexical scanners to pass location information of a matched token to the parser in parallel with a returned token. It is available only when %lsp-needed, %ltype or %locationstruct has been defined.

 

Lexical scanners may be offered the facility to assign a value to this variable in parallel with a returned token. In order to allow a scanner access to d_loc__, d_loc__’s address should be passed to the scanner. This can be realized, for example, by defining a member void setLoc(STYPE__ *) in the lexical scanner, which is then called from the parser’s constructor as follows:

            d_scanner.setSLoc(&d_loc__);
       
    

Subsequently, the lexical scanner may assign a value to the parser’s d_loc__ variable through the pointer to d_loc__ stored inside the lexical scanner.

o

LTYPE__ d_lsp__:

 

The location stack pointer. Do not modify.

o

size_t d_nErrors__:

 

The number of errors counted by parse. It is initialized by the parser’s base class initializer, and is updated while parse executes. When parse has returned it contains the total number of errors counted by parse. Errors are not counted if suppressed (i.e., if d_acceptedTokens__ is less than d_requiredTokens__).

o

size_t d_nextToken__:

 

A pending token. Do not modify.

o

size_t d_requiredTokens__:

 

Defines the minimum number of accepted tokens that the parse function must have processed before a syntactic error can be generated.

o

int d_state__:

 

The current parsing state. Do not modify.

o

int d_token__:

 

The current token. Do not modify.

o

STYPE__ d_val__:

 

The semantic value of a returned token or non-terminal symbol. With non-terminal tokens it is assigned a value through the action rule’s symbol $$. Lexical scanners may be offered the facility to assign a semantic value to this variable in parallel with a returned token. In order to allow a scanner access to d_val__, d_val__’s address should be passed to the scanner. This can be realized, for example, by passing d_val__’s address to the lexical scanner’s constructor. Subsequently, the lexical scanner may assign a value to the parser’s d_val__ variable through the pointer to d_val__ stored in a data member of the lexical scanner. Note that in some cases this approach must be used to make available the correct semantic value to the parser. In particular, when a grammar state defines multiple reductions, depending on the next token, the reduction’s action only takes place following the retrieval of the next token, thus losing the initially matched token text.

o

LTYPE__ d_vsp__:

 

The semantic value stack pointer. Do not modify.

 

10. TYPES AND VARIABLES IN THE ANONYMOUS NAMESPACE¶

In the file defining the parse function the following types and variables are defined in the anonymous namespace. These are mentioned here for the sake of completeness, and are not normally accessible to other parts of the parser.

o

char const author[]:

 

Defining the name and e-mail address of Bisonc++’s author.

o

ReservedTokens:

 

This enumeration defines some token values used internally by the parsing functions. They are:

    PARSE_ACCEPT   =  0,
    _UNDETERMINED_ = -2,
    _EOF_          = -1,
    _error_        = 256,
       
    

These tokens are used by the parser to determine whether another token should be requested from the lexical scanner, and to handle error-conditions.

o

StateType:

 

This enumeration defines several moe token values used internally by the parsing functions. They are:

        NORMAL,
        ERR_ITEM,
        REQ_TOKEN,
        ERR_REQ,    // ERR_ITEM | REQ_TOKEN
        DEF_RED,    // state having default reduction
        ERR_DEF,    // ERR_ITEM | DEF_RED
        REQ_DEF,    // REQ_TOKEN | DEF_RED
        ERR_REQ_DEF // ERR_ITEM | REQ_TOKEN | DEF_RED
       
    

These tokens are used by the parser to define the types of the various states of the analyzed grammar.

o

PI__ (Production Info):

 

The type defines a struct containing information about the production rules that were used by a grammar.

 

Its first field contains the identification number of a production’s defining non-terminal;

 

Its second field defines the number of elements of a production

o

SR__ (Shift-Reduce Info):

 

This struct provides the shift/reduce information for the various grammatic states. SR__ values are collected in arrays, one array per grammatic state. These array, named s_<nr>, where tt<nr> is a state number are defined in the anonymous namespace as well. The SR__ elements consist of two unions, defining fields that are applicable to, respectively, the first, intermediate and the last array elements.

 

The first element of each array consists of (1st field) a StateType and (2nd field) the index of the last array element; intermediate elements consist of (1st field) a symbol value and (2nd field) (if negative) the production rule number reducing to the indicated symbol value or (if positive) the next state when the symbol given in the 1st field is the current token; the last element of each array consists of (1st field) a placeholder for the current token and (2nd field) the (negative) rule number to reduce to by default or the (positive) number of an error-state to go to when an erroneous token has been retrieved. If the 2nd field is zero, no error or default action has been defined for the state, and error-recovery is attepted.

o

STACK_EXPANSION:

 

An enumeration value specifying the number of additional elements that are added to the state- and semantic value stacks when full.

o

PI__ (Production Info):

 

This struct provides information about production rules. It has two fields: d_nonTerm is the identification number of the production’s non-terminal, d_size represents the number of elements of the productin rule.

o

static PI__ s_productionInfo:

 

Used internally by the parsing function.

o

static SR__ s_<nr>[]:

 

Here, <nr> is a numerical value representing a state number. Used internally by the parsing function.

o

static SR__ *s_state[]:

 

Used internally by the parsing function.

 

11. RESTRICTIONS ON TOKEN NAMES¶

To avoid collisions with names defined by the parser’s (base) class, the following identifiers should not be used as token names:

o

Identifiers ending in two underscores;

o

Any of the following identifiers: ABORT, ACCEPT, ERROR, clearin, debug, or setDebug.

 

12. OBSOLETE SYMBOLS¶

All DECLARATIONS and DEFINE symbols not listed above but defined in bison++ are obsolete with bisonc++. In particular, there is no %header{ ... %} section anymore. Also, all DEFINE symbols related to member functions are now obsolete. There is no need for these symbols anymore as they can simply be declared in the class header file and defined elsewhere.

13. EXAMPLE¶

Using a fairly worn-out example, we’ll construct a simple calculator below. The basic operators as well as parentheses can be used to specify expressions, and each expression should be terminated by a newline. The program terminates when a q is entered. Empty lines result in a mere prompt. First an associated grammar is constructed. When a syntactic error is encountered all tokens are skipped until then next newline and a simple message is printed using the default error function. It is assumed that no semantic errors occur (in particular, no divisions by zero). The grammar is decorated with actions performed when the corresponding grammatical production rule is recognized. The grammar itself is rather standard and straightforward, but note the first part of the specification file, containing various other directives, among which the %scanner directive, resulting in a composed d_scanner object as well as an implementation of the member function int lex. In this example, a common Scanner class construction strategy was used: the class Scanner was derived from the class yyFlexLexer generated by flex++(1). The actual process of constructing a class using flex++(1) is beyond the scope of this man-page, but flex++(1)’s specification file is mentioned below, to further complete the example. Here is bisonc++’s input file:

%filenames parser
%scanner ../scanner/scanner.h

                                // lowest precedence
%token  NUMBER                  // integral numbers
        EOLN                    // newline

%left   ’+’ ’-’ 
%left   ’*’ ’/’ 
%right  UNARY
                                // highest precedence 

%%

expressions:
    expressions 
    evaluate
|
    prompt
;

evaluate:
    alternative
    prompt
;

prompt:
    {
        prompt();
    }
;

alternative:
    expression
    EOLN
    {
        cout << $1 << endl;
    }
|
    ’q’
    done
|
    EOLN
|
    error
    EOLN
;

done:
    {
        cout << "Done.\n";
        ACCEPT();
    }
;

expression:
    expression 
    ’+’
    expression
    {
        $$ = $1 + $3;
    }
|
    expression 
    ’-’
    expression
    {
        $$ = $1 - $3;
    }
|
    expression 
    ’*’
    expression
    {
        $$ = $1 * $3;
    }
|
    expression 
    ’/’
    expression
    {
        $$ = $1 / $3;
    }
|
    ’-’             
    expression      %prec UNARY
    {
        $$ = -$2;
    }
|
    ’+’             
    expression      %prec UNARY
    {
        $$ = $2;
    }
|
    ’(’
    expression
    ’)’
    {
        $$ = $2;
    }
|
    NUMBER
    {
        $$ = atoi(d_scanner.YYText());
    }
;

Next, bisonc++ processes this file. In the process, bisonc++ generates the following files from its skeletons:

o

The parser’s base class, which is not modified by the programmer at all:

#ifndef ParserBase_h_included
#define ParserBase_h_included

#include <vector>
#include <iostream>


namespace // anonymous
{
    struct PI__;
}


class ParserBase
{
    public:
// $insert tokens

    // Symbolic tokens:
    enum Tokens__
    {
        NUMBER = 257,
        EOLN,
        UNARY,
    };

// $insert STYPE
typedef int STYPE__;

    private:
        int d_stackIdx__;
        std::vector<size_t>   d_stateStack__;
        std::vector<STYPE__>  d_valueStack__;

    protected:
        enum Return__
        {
            PARSE_ACCEPT__ = 0,   // values used as parse()’s return values
            PARSE_ABORT__  = 1
        };
        enum ErrorRecovery__
        {
            DEFAULT_RECOVERY_MODE__,
            UNEXPECTED_TOKEN__,
        };
        bool        d_debug__;
        size_t      d_nErrors__;
        size_t      d_requiredTokens__;
        size_t      d_acceptedTokens__;
        int         d_token__;
        int         d_nextToken__;
        size_t      d_state__;
        STYPE__    *d_vsp__;
        STYPE__     d_val__;

        ParserBase();

        void ABORT() const;
        void ACCEPT() const;
        void ERROR() const;
        void checkEOF__() const;
        void clearin();
        bool debug() const;
        void pop__(size_t count = 1);
        void push__(size_t nextState);
        void popToken__();
        void pushToken__(int token);
        void reduce__(PI__ const &productionInfo);
        void errorVerbose__();
        size_t top__() const;

    public:
        void setDebug(bool mode);
}; 

inline bool ParserBase::debug() const
{
    return d_debug__;
}

inline void ParserBase::setDebug(bool mode)
{
    d_debug__ = mode;
}

inline void ParserBase::ABORT() const
{
    throw PARSE_ABORT__;
}

inline void ParserBase::ACCEPT() const
{
    throw PARSE_ACCEPT__;
}

inline void ParserBase::ERROR() const
{
    throw UNEXPECTED_TOKEN__;
}


// As a convenience, when including ParserBase.h its symbols are available as
// symbols in the class Parser, too.
#define Parser ParserBase


#endif



    

 

o

The parser class parser.h itself. In the grammar specification various member functions are used (e.g., done) and prompt. These functions are so small that they can very well be implemented inline. Note that done calls ACCEPT to terminate further parsing. ACCEPT and related members (e.g., ABORT) can be called from any member called by parse. As a consequence, action blocks could contain mere function calls, rather than several statements, thus minimizing the need to rerun bisonc++ when an action is modified.

Once bisonc++ had created parser.h it was augmented with the required additional members, resulting in the following final version:

#ifndef Parser_h_included
#define Parser_h_included

// $insert baseclass
#include "parserbase.h"
// $insert scanner.h
#include "../scanner/scanner.h"


#undef Parser
class Parser: public ParserBase
{
    // $insert scannerobject
    Scanner d_scanner;
        
    public:
        int parse();

    private:
        void error(char const *msg);    // called on (syntax) errors
        int lex();                      // returns the next token from the
                                        // lexical scanner. 
        void print();                   // use, e.g., d_token, d_loc

        void prompt();
        void done();

    // support functions for parse():
        void executeAction(int ruleNr);
        void errorRecovery();
        int lookup(bool recovery);
        void nextToken();
};

inline void Parser::error(char const *msg)
{
    std::cerr << msg << ’\n’;
}

// $insert lex
inline int Parser::lex()
{
    return d_scanner.yylex();
}

inline void Parser::print()      // use d_token, d_loc
{}

inline void Parser::prompt()
{
    std::cout << "? " << std::flush;
}

inline void Parser::done()
{
    std::cout << "Done\n";
    ACCEPT();
}

#endif

    

 

o

To complete the example, the following lexical scanner specification was used:

%{
    #define _SKIP_YYFLEXLEXER_
    #include "scanner.ih"

    #include "../parser/parser.h"
%}

%option yyclass="Scanner" outfile="yylex.cc"
%option c++ 8bit warn noyywrap yylineno

%%

[ \t]+                          // skip white space

\n                              return Parser::EOLN;

[0-9]+                          return Parser::NUMBER;

.                               return yytext[0];


%%



    

 

o

Since no member functions other than parse were defined in separate source files, only parse includes parser.ih. Since cerr is used in the grammar’s actions, a using namespace std or comparable statement is required. This was effectuated from parser.ih Here is the implementation header declaring the standard namespace:

// include this file in the sources of the class Calculator, 
// and add any includes etc. that are only needed for 
// the compilation of these sources.

// include the file defining the parser class:
#include "parser.h"

// UN-comment if you don’t want to prefix std:: 
// for every symbol defined in the std. namespace:

using namespace std;

    

 

The implementation of the parsing member function parse is basically irrelevant, since it should not be modified by the programmer. It was written on the file parse.cc.

o

Finally, here is the program offering our simple calculator:

#include "parser/parser.h"

int main()
{
    Parser calculator;
    return calculator.parse();
}

    

 

 

14. USING PARSER-CLASS SYMBOLS IN LEXICAL SCANNERS¶

Note here that although the file parserbase.h, defining the parser class’ base-class, rather than the header file parser.h defining the parser class is included, the lexical scanner may simply return tokens of the class Calculator (e.g., Calculator::NUMBER rather than CalculatorBase::NUMBER). In fact, using a simple #define - #undef pair generated by the bisonc++ respectively at the end of the base class header the file and just before the definition of the parser class itself it is the possible to assume in the lexical scanner that all symbols defined in the the parser’s base class are actually defined in the parser class itself. It the should be noted that this feature can only be used to access base class the enum and types. The actual parser class is not available by the time the the lexical scanner is defined, thus avoiding circular class dependencies.

15. FILES¶

o

bisonc++base.h: skeleton of the parser’s base class;

o

bisonc++.h: skeleton of the parser class;

o

bisonc++.ih: skeleton of the implementation header;

o

bisonc++.cc: skeleton of the member parse;

o

bisonc++polymorphic: skeleton of the declarations used by %polymorphic;

o

bisonc++polymorphic.inline: skeleton of the inline implementations of the members declared in bisonc++polymorphic.

 

16. SEE ALSO¶

bison(1), bison++(1), bison.info (using texinfo), flex++(1) Lakos, J. (2001) Large Scale C++ Software Design, Addison Wesley. Aho, A.V., Sethi, R., Ullman, J.D. (1986) Compilers, Addison Wesley.

17. BUGS¶

Discontinued option:

o

--include-only

 

To avoid collisions with names defined by the parser’s (base) class, the following identifiers should not be used as token nams:

o

Identifiers ending in two underscores;

o

Any of the following identifiers: ABORT, ACCEPT, ERROR, clearin, debug, error, or setDebug.

 

When re-using files generated by bisonc++ before version 2.0.0, minor hand-modification might be necessary. The identifiers in the following list (defined in the parser’s base class) now have two underscores affixed to them: LTYPE, STYPE and Tokens. When using classes derived from the generated parser class, the following identifiers are available in such derived classes: DEFAULT_RECOVERY_MODE, ErrorRecovery, Return, UNEXPECTED_TOKEN, d_debug, d_loc, d_lsp, d_nErrors, d_nextToken, d_state, d_token, d_val, and d_vsp. When used in derived classes, they too need two underscores affixed to them. The member function void lookup (< 1.00) was replaced by int lookup. When regenerating parsers created by early versions of bisonc++ (versions before version 1.00), lookup’s prototype should be corrected by hand, since bisonc++ will not by itself rewrite the parser class’s header file. The Semantic parser, mentioned in bison++(1) is not implemented in bisonc++(1). According to bison++(1) the semantic parser was not available in bison++ either. It is possible that the Pure parser is now available through the --thread-safe option.

18. ABOUT bisonc++¶

Bisonc++ was based on bison++, originally developed by Alain Coetmeur (coetmeur@icdc.fr), R&D department (RDT), Informatique-CDC, France, who based his work on bison, GNU version 1.21. Bisonc++ version 0.98 and beyond is a complete rewrite of an LALR-1 parser generator, closely following the construction process as described in Aho, Sethi and Ullman’s (1986) book Compilers (i.e., the Dragon book). It the uses same grammar specification as bison and bison++, and it uses practically the same options and directives as bisonc++ versions earlier than 0.98. Variables, declarations and macros that are obsolete were removed.

AUTHOR¶

Frank B. Brokken (f.b.brokken@rug.nl).