man bisonc++ (3): Application programmer's interface of bisonc++ generated classes

DESCRIPTION

Bisonc++ derives from bison++(1), originally derived from bison(1). Like these programs bisonc++ generates a parser for an LALR(1) grammar. Bisonc++ generates C++ code: an expandable C++ class.

Refer to bisonc++(1) for a general overview. This manual page covers the application programmer's interface of classes generated by bisonc++. It contains the following sections:

DESCRIPTION: this section;
PUBLIC MEMBERS AND -TYPES: members and types that can be used by calling software;
PRIVATE ENUMS AND -TYPES: enumerations and types only available to the Parser class;
PRIVATE MEMBER FUNCTIONS: member functions that are only available to the Parser class;
PRIVATE DATA MEMBERS: data members that are only available to the Parser class;
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++;
SEE ALSO: references to other programs and documentation;
AUTHOR: at the end of this man-page.

PUBLIC MEMBERS, TYPES, AND ENUMS

Parser classes generated by bisonc++ offer the following public members and types (in the following overview parser class-name prefixes (e.g., Parser::) prefixes were omitted):

DebugMode__:
The values of this enum are used to configure the type of debug information that will be displayed (assuming that the debug option/directive was specified when bisonc++ generated the parser's code). It has three values:
OFF: no debug information is displayed when the generated parser's parse function is called;
ON: extensive debug information about the parsing process is displayed when the generated parser's parse function is called;
ACTIONCASES: just before executing the grammar's action blocks the action block number is written to the standard output stream. These action block numbers refer to case labels of the switch that is defined in the parser's executeAction function. It is commonly used to find the action block where a fatal semantic value mismatch was observed.
The bit_or operator can be used to combine ON and ACTIONCASES (see the member function setDebug(DebugMode__ mode) below).
LTYPE__:
The parser's location type (user-definable). Available only when either %lsp-needed, %ltype or %locationstruct has been declared.
STYPE__:
The parser's stack-type (user-definable), defaults to int.
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.
int parse():
The parser's parsing member function. It returns 0 when parsing was successfully completed; 1 if errors were encountered while parsing the input.
void setDebug(bool mode):
This member can be used to activate or deactivate the debug-code compiled into the parsing function. It is always defined but is only operational if the debug directive option was specified when bisonc++ generated the parse function. If so, it is not active by default; to activate the debug output call setDebug(true), to suppress the debug output call setDebug(false).
void setDebug(DebugMode__ mode):
This member can also be used to activate or deactivate the debug-code compiled into the parsing function. Like setDebug(bool) it is always defined but only operational if the debug directive option was specified when bisonc++ generated the parse function. If so, it is not active by default; to activate, call setDebug(Parser::ON), setDebug(Parser::ACTIONCASES), or setDebug(Parser::ON | Parser::ACTIONCASES). To suppress the debug code output call setDebug(Parser__::OFF) or simply setDebug(false).

When the %polymorphic directive is used:

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.
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.

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.

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).
Base::Return__:
This enumeration defines two values:
```
    PARSE_ACCEPT = 0,
    PARSE_ABORT = 1
        
```
(which are of course the parse function's return values).

When the %polymorphic directive is used:

Meta__::sizeofTag__:
sizeofTag__ defines the number of tags that were defined for polymorphic semantic values.

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.

Base::ParserBase():
Used internally.
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.
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.
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 must probably be reloaded with new information as well.
bool Base::debug() const:
This member returns the current value of the debug variable.
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 results in the parser executing its 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.
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.
void errorRecovery__():
Used internally.
void Base::errorVerbose__():
Used internally.
void exceptionHandler__(std::exception const &exc):
This member's default implementation is provided inline in the parser.ih internal header file. It consists of a mere throw statement, rethrowing a caught exception.
The parse member function's body essentially consists of a while statement, in which the next token is obtained via the parser's lex member. This token is then processed according to the current state of the parsing process. This may result in executing actions over which the parsing process has no control and which may result in exceptions being thrown.
Such exceptions do not necessarily have to terminate the parsing process: they could be thrown by code, linked to the parser, that simply checks for semantic errors (like divisions by zero) throwing exceptions if such errors are observed.
The member exceptionHandler__ receives and may handle such exceptions without necessarily ending the parsing process. It receives any std::exception thrown by the parser's actions, as though the action block itself was surrounded by a try ... catch statement. It is of course still possible to use an explicit try ... catch statement within action blocks. However, exceptionHandler__ can be used to factor out code that is common to various action blocks.
The next example shows an explicit implementation of exceptionHandler__: any std::exception thrown by the parser's action blocks is caught, showing the exception's message, and increasing the parser's error count. After this parsing continues as if no exception had been thrown:
```
void Parser::exceptionHandler__(std::exception const &exc)
{
    std::cout << exc.what() << '\n';
    ++d_nErrors__;
}
        
```
Note: Parser-class header files (e.g., Parser.h) and parser-class internal header files (e.g., Parser.ih) generated with bisonc++ < 4.02.00 require two small hand-modifications when using bisonc++ >= 4.02.00:

In Parser.h, just below the declaration

void print__();

add:

void exceptionHandler__(std::exception const &exc);

In Parser.ih, assuming the name of the generated class is `Parser', add the following member definition (if a namespace is used: within the namespace's scope):
```
inline void Parser::exceptionHandler__(std::exception const &exc)
{
    throw;  // re-implement to handle exceptions thrown by actions
}
    
```
void executeAction(int):
Used internally.
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'.
int lookup(bool):
Used internally.
void nextToken():
Used internally.
void Base::pop__():
Used internally.
void Base::popToken__():
Used internally.
void print__()():
Used internally.
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.
void Base::push__():
Used internally.
void Base::pushToken__():
Used internally.
void Base::reduce__():
Used internally.
void Base::symbol__():
Used internally.
void Base::top__():
Used internally.

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.

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.
bool d_actionCases__:
When the debug option has been specified, this variable (false by default) determines whether the number of action block which is about to be executed by the parser's member executeAction will be displayed to the standard output stream.
bool d_debug__:
When the debug option has been specified, this variable (true by default) determines whether debug information is actually displayed.
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.
LTYPE__ d_lsp__:
The location stack pointer. Do not modify.
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__).
size_t d_nextToken__:
A pending token. Do not modify.
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.
int d_state__:
The current parsing state. Do not modify.
int d_token__:
The current token. Do not modify.
STYPE__ d_val__:
The semantic value of a returned token or nonterminal symbol. With nonterminal 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 the correct semantic value available 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.
If STYPE is a polymorphic semantic value, specific requirements for assigning values to d_val__ apply. .
LTYPE__ d_vsp__:
The semantic value stack pointer. Do not modify.

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.

char const author[]:
Defining the name and e-mail address of Bisonc++'s author.
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.

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.

PI__ (Production Info):
This struct provides information about production rules. It has two fields: d_nonTerm is the identification number of the production's nonterminal, d_size represents the number of elements of the productin rule.
static PI__ s_productionInfo:
Used internally by the parsing function.
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.
STACK_EXPANSION__:
An enumeration value specifying the number of additional elements that are added to the state- and semantic value stacks when full.
static SR__ s_<nr>[]:
Here, <nr> is a numerical value representing a state number. Used internally by the parsing function.
static SR__ *s_state[]:
Used internally by the parsing function.

AUTHOR

Frank B. Brokken ([email protected]).