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vcsn::algebra::Parser Struct Template Reference
[Series]

Parser class used in the parse() function. More...

List of all members.

Public Methods
void	parse (Element< S, T > &exp)
	Do the parsing.
bool	error () const
	Return true when an error occured.
const std::string &	error_msg () const
	Return the error message.
Protected Methods
void	parse_error (const std::string &msg="parse_error.") throw (const std::string&)
	Generate a parse error.
void	accept (token_e tok)
	Accept token, or generate an error. More...
void	parse_exp (Element< S, T > &exp)
	exp ::= term ('+' term)*.
void	parse_term (Element< S, T > &exp)
	term ::= right_weighted ('.'? right_weighted)*.
void	parse_right_weighted (Element< S, T > &exp)
	right_weighted ::= left_weighted (' ' weight)*.
void	parse_left_weighted (Element< S, T > &exp)
	left_weighted ::= weight ' ' left_weighted | stared.
void	parse_stared (Element< S, T > &exp)
	stared ::= factor '*'*.
void	parse_factor (Element< S, T > &exp)
	factor ::= 1 | 0 | word | '(' exp ')'.
void	trace (const std::string &msg)
	Trace parsing.
template<class Misc> void	trace (const std::string &msg, const Misc &v)
	Trace parsing.

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Detailed Description

template<class S, class T>
struct vcsn::algebra::Parser< S, T >

Parser class used in the parse() function.

This class handles rational expression parsing, once a Lexer has been created.

Ideally, we would like to parse:

 exp ::= '(' exp ')'
     |   exp '+' exp
     |   exp '.' exp
     |   exp exp
     |   exp '*'
     |   weight ' ' exp
     |   exp ' ' weight
     |   0
     |   1
     |   word
 

But this grammar has to be changed to allow a classical LL(2) parsing:

 exp		::= term ('+' term)*
 term		::= right_weighted ('.'? right_weighted)*
 right_weighted	::= left_weighted (' ' weight)*
 left_weighted	::= weight ' ' left_weighted
                  |   stared
 stared		::= factor '*'*
 factor		::= '(' exp ')' | word | 0 | 1
 

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Member Function Documentation

void accept (  token_e    tok )  [inline, protected]

Accept token, or generate an error. This function asks the lexer whether the first input token matches the argument or not. When matching is successfull, the first input token is eaten, an error is risen else. Parameters: tok  The token to match.

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