The recommended base class for lexers generated by LLLPG, when not using the inputSource option. More...

Source file:

/Core/Loyc.Syntax/Lexing/BaseLexer.cs

Inheritance diagram for Loyc.Syntax.Lexing.BaseLexer< CharSrc >:

Remarks

The recommended base class for lexers generated by LLLPG, when not using the inputSource option.

If you are using the inputSource and inputClass options of, LLLPG, use LexerSource{CharSource} instead. If you want to write a lexer that implements ILexer{Tok} (so it is compatible with postprocessors like IndentTokenGenerator and TokensToTree), use BaseILexer{CharSrc,Tok} as your base class instead.

This class contains many methods required by LLLPG, such as NewSet, LA(int), LA0, Skip, Match(...), and TryMatch(...), along with a few properties that are not used by LLLPG that you still might want to have around, such as FileName, CharSource and SourceFile.

It also implements the caching behavior for which ICharSource was created. See the documentation of ICharSource for more information.

All lexers derived from BaseLexer should call AfterNewline() at the end of their newline rule, in order to increment the current line number. Alternately, your lexer can borrow the newline parser built into BaseLexer, which is called Newline() and calls AfterNewline() for you. It is possible to have LLLPG treat this method as a rule, and tell LLLPG the meaning of the rule like this:

extern token Newline @[ '\r' '\n'? | '\n' ];
// BaseLexer also defines a Spaces() method, which behaves like this:
extern token Spaces  @[ (' '|'\t')* ]; 

The extern modifier tells LLLPG not to generate code for the rule, but the rule must still have a body so that LLLPG can perform prediction.

By default, errors are handled by throwing FormatException. The recommended way to alter this behavior is to change the ErrorSink property. For example, set it to MessageSink.Console to send errors to the console, or use MessageSink.FromDelegate to provide a custom handler.

Template Parameters

CharSrc A class that implements ICharSource. In order to write lexers that can accept any source of characters, set CharSrc=ICharSource. For maximum performance when parsing strings (or to avoid memory allocation), set CharSrc=UString (UString is a wrapper around System.String that, among other things, implements ICharSource; please note that C# will implicitly convert normal strings to UString for you).

Type Constraints

CharSrc

:

ICharSource

Nested classes
struct	SavePosition
	A helper class used by LLLPG for backtracking. More...

Public static fields
static readonly IMessageSink	FormatExceptionErrorSink
	Throws FormatException when it receives an error. Non-errors are sent to MessageSink.Current. More...

Properties
IMessageSink	ErrorSink `[get, set]`
	Gets or sets the object to which error messages are sent. The default object is FormatExceptionErrorSink, which throws FormatException if an error occurs. More...

int	LA0 `[get, set]`

CharSrc	CharSource `[get]`

string	FileName `[get]`

int	InputPosition `[get, set]`

LexerSourceFile< CharSrc >	SourceFile `[get]`

int	LineNumber `[get]`
	Current line number. Starts at 1 for the first line, unless derived class changes it. More...

int	LineStartAt `[get]`
	Index at which the current line started. More...

Public Member Functions
	BaseLexer (CharSrc chars, string fileName="", int inputPosition=0, bool newSourceFile=true)
	Initializes BaseLexer. More...

virtual void	Reset (CharSrc chars, string fileName="", int inputPosition=0, bool newSourceFile=true)
	Reinitializes the object. This method is called by the constructor. More...

SourcePos	IndexToLine (int index)
	Returns the position in a source file of the specified index. More...

Protected Member Functions
void	Reset ()

int	LA (int i)

void	Skip ()
	Increments InputPosition. Called by LLLPG when prediction already verified the input (and caller doesn't save LA(0)) More...

virtual void	AfterNewline ()
	The lexer must call this method exactly once after it advances past each newline, even inside comments and strings. This method keeps the LineNumber and LineStartAt properties updated. More...

void	Newline ()
	Default newline parser that matches ' ' or '' unconditionally. More...

void	Spaces ()
	Skips past any spaces at the current position. Equivalent to `rule Spaces @[ (' '\|'')* ]` in LLLPG. More...

int	MatchAny ()

int	Match (HashSet< int > set)

int	Match (int a)

int	Match (int a, int b)

int	Match (int a, int b, int c)

int	Match (int a, int b, int c, int d)

int	MatchRange (int aLo, int aHi)

int	MatchRange (int aLo, int aHi, int bLo, int bHi)

int	MatchExcept ()

int	MatchExcept (HashSet< int > set)

int	MatchExcept (int a)

int	MatchExcept (int a, int b)

int	MatchExcept (int a, int b, int c)

int	MatchExcept (int a, int b, int c, int d)

int	MatchExceptRange (int aLo, int aHi)

int	MatchExceptRange (int aLo, int aHi, int bLo, int bHi)

bool	TryMatch (HashSet< int > set)

bool	TryMatch (int a)

bool	TryMatch (int a, int b)

bool	TryMatch (int a, int b, int c)

bool	TryMatch (int a, int b, int c, int d)

bool	TryMatchRange (int aLo, int aHi)

bool	TryMatchRange (int aLo, int aHi, int bLo, int bHi)

bool	TryMatchExcept ()

bool	TryMatchExcept (HashSet< int > set)

bool	TryMatchExcept (int a)

bool	TryMatchExcept (int a, int b)

bool	TryMatchExcept (int a, int b, int c)

bool	TryMatchExcept (int a, int b, int c, int d)

bool	TryMatchExceptRange (int aLo, int aHi)

bool	TryMatchExceptRange (int aLo, int aHi, int bLo, int bHi)

virtual void	Check (bool expectation, string expectedDescr="")

virtual void	Error (int lookaheadIndex, string message)
	This method is called to handle errors that occur during lexing. More...

virtual void	Error (int lookaheadIndex, string format, params object[] args)
	This method is called to format and handle errors that occur during lexing. The default implementation sends errors to ErrorSink, which, by default, throws a FormatException. More...

virtual void	Error (bool inverted, int range0lo, int range0hi)

virtual void	Error (bool inverted, params int[] ranges)

virtual void	Error (bool inverted, IList< int > ranges)

virtual void	Error (bool inverted, HashSet< int > set)

string	RangesToString (IList< int > ranges)
	Converts a list of character ranges to a string, e.g. for input list {'','','a','z'}, the output is "'*' 'a'..'z'". More...

void	PrintChar (int c, StringBuilder sb)
	Prints a character as a string, e.g. `'a' -> "'a'"`, with the special value -1 representing EOF, so PrintChar(-1, ...) == "EOF". More...

Static Protected Member Functions
static HashSet< int >	NewSet (params int[] items)

static HashSet< int >	NewSetOfRanges (params int[] ranges)

Protected fields
int	CachedBlockSize = 128

int	_lineStartAt

int	_lineNumber = 1

Constructor & Destructor Documentation

Loyc.Syntax.Lexing.BaseLexer< CharSrc >.BaseLexer	(	CharSrc	chars,
		string	fileName = `""`,
		int	inputPosition = `0`,
		bool	newSourceFile = `true`
	)

inline

Initializes BaseLexer.

Parameters

chars	A source of characters, e.g. UString.
fileName	A file name associated with the characters, which will be used for error reporting.
inputPosition	A location to start lexing (normally 0). Careful: If you're starting to lex in the middle of the file, the LineNumber still starts at 1, and (if `newSourceFile` is true) the SourceFile object may or may not discover line breaks prior to the starting point, depending on how it is used.
newSourceFile	Whether to create a LexerSourceFile{C} object (an implementation of ISourceFile) to keep track of line boundaries. The SourceFile property will point to this object, and it will be null if this parameter is false. Using 'false' will avoid memory allocation, but prevent you from mapping character positions to line numbers and vice versa. However, this object will still keep track of the current LineNumber and LineStartAt (the index where the current line started) when this parameter is false.

Member Function Documentation

virtual void Loyc.Syntax.Lexing.BaseLexer< CharSrc >.AfterNewline ( )

inlineprotectedvirtual

The lexer must call this method exactly once after it advances past each newline, even inside comments and strings. This method keeps the LineNumber and LineStartAt properties updated.

Reimplemented in Loyc.Syntax.Lexing.BaseILexer< CharSrc, Token >, and Loyc.Syntax.Lexing.LexerSource< CharSrc >.

virtual void Loyc.Syntax.Lexing.BaseLexer< CharSrc >.Error	(	int	lookaheadIndex,
		string	message
	)

inlineprotectedvirtual

This method is called to handle errors that occur during lexing.

Parameters

lookaheadIndex	Index where the error occurred, relative to the current InputPosition (i.e. InputPosition + lookaheadIndex is the position of the error).
message	An error message, not including the error location.

Reimplemented in Loyc.Syntax.Lexing.LexerSourceWorkaround< CharSrc >, and Loyc.Syntax.Lexing.LexerSource< CharSrc >.

virtual void Loyc.Syntax.Lexing.BaseLexer< CharSrc >.Error	(	int	lookaheadIndex,
		string	format,
		params object[]	args
	)

inlineprotectedvirtual

This method is called to format and handle errors that occur during lexing. The default implementation sends errors to ErrorSink, which, by default, throws a FormatException.

Parameters

lookaheadIndex	Index where the error occurred, relative to the current InputPosition (i.e. InputPosition + lookaheadIndex is the position of the error).
format	An error description with argument placeholders.
args	Arguments to insert into the error message.

Reimplemented in Loyc.Syntax.Lexing.LexerSourceWorkaround< CharSrc >, and Loyc.Syntax.Lexing.LexerSource< CharSrc >.

SourcePos Loyc.Syntax.Lexing.BaseLexer< CharSrc >.IndexToLine ( int index )

inline

Returns the position in a source file of the specified index.

If index is negative, this should return a SourcePos where Line and PosInLine are zero (signifying an unknown location). If index is beyond the end of the file, this should retun the final position in the file.

Implements Loyc.Syntax.IIndexToLine.

void Loyc.Syntax.Lexing.BaseLexer< CharSrc >.Newline ( )

inlineprotected

Default newline parser that matches '
' or '' unconditionally.

You can use this implementation in an LLLPG lexer with "extern", like so: extern rule Newline @[ '' + ' '? | ' ' ]; By using this implementation everywhere in the grammar in which a newline is allowed (even inside comments and strings), you can ensure that AfterNewline() is called, so that the line number is updated properly.

void Loyc.Syntax.Lexing.BaseLexer< CharSrc >.PrintChar	(	int	c,
		StringBuilder	sb
	)

inlineprotected

Prints a character as a string, e.g. 'a' -> "'a'", with the special value -1 representing EOF, so PrintChar(-1, ...) == "EOF".

string Loyc.Syntax.Lexing.BaseLexer< CharSrc >.RangesToString ( IList< int > ranges )

inlineprotected

Converts a list of character ranges to a string, e.g. for input list {'*','*','a','z'}, the output is "'*' 'a'..'z'".

virtual void Loyc.Syntax.Lexing.BaseLexer< CharSrc >.Reset	(	CharSrc	chars,
		string	fileName = `""`,
		int	inputPosition = `0`,
		bool	newSourceFile = `true`
	)

inlinevirtual

Reinitializes the object. This method is called by the constructor.

See the constructor for documentation of the parameters.

This method can be used to avoid memory allocations when you need to parse many small strings in a row. If that's your goal, you should set the newSourceFile parameter to false if possible.

Reimplemented in Loyc.Syntax.Lexing.BaseILexer< CharSrc, Token >, and Loyc.Syntax.Lexing.LexerSource< CharSrc >.

void Loyc.Syntax.Lexing.BaseLexer< CharSrc >.Skip ( )

inlineprotected

Increments InputPosition. Called by LLLPG when prediction already verified the input (and caller doesn't save LA(0))

void Loyc.Syntax.Lexing.BaseLexer< CharSrc >.Spaces ( )

inlineprotected

Skips past any spaces at the current position. Equivalent to rule Spaces @[ (' '|'')* ] in LLLPG.

Member Data Documentation

readonly IMessageSink Loyc.Syntax.Lexing.BaseLexer< CharSrc >.FormatExceptionErrorSink

static

Initial value:

= MessageSink.FromDelegate(
            (sev, location, fmt, args) => { 
                if (sev >= Severity.Error)
                    throw new FormatException(MessageSink.LocationString(location) + ": " + Localize.Localized(fmt, args));
                else
                    MessageSink.Current.Write(sev, location, fmt, args);
            })

Throws FormatException when it receives an error. Non-errors are sent to MessageSink.Current.

Property Documentation

IMessageSink Loyc.Syntax.Lexing.BaseLexer< CharSrc >.ErrorSink

getset

Gets or sets the object to which error messages are sent. The default object is FormatExceptionErrorSink, which throws FormatException if an error occurs.

int Loyc.Syntax.Lexing.BaseLexer< CharSrc >.LineNumber

get

Current line number. Starts at 1 for the first line, unless derived class changes it.

int Loyc.Syntax.Lexing.BaseLexer< CharSrc >.LineStartAt

getprotected

Index at which the current line started.