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Lexing(3)				  OCaml library 				Lexing(3)

NAME
       Lexing - The run-time library for lexers generated by ocamllex.

Module
       Module	Lexing

Documentation
       Module Lexing
	: sig end

       The run-time library for lexers generated by ocamllex .

       === Positions ===

       type position = {
	pos_fname : string ;
	pos_lnum : int ;
	pos_bol : int ;
	pos_cnum : int ;
	}

       A  value of type position describes a point in a source file.  pos_fname is the file name;
       pos_lnum is the line number; pos_bol is the offset of the beginning of the line (number of
       characters between the beginning of the lexbuf and the beginning of the line); pos_cnum is
       the offset of the position (number of characters between the beginning of the  lexbuf  and
       the position).  The difference between pos_cnum and pos_bol is the character offset within
       the line (i.e. the column number, assuming each character is one column wide).

       See the documentation of type lexbuf for information about how the lexing engine will man-
       age positions.

       val dummy_pos : position

       A value of type position , guaranteed to be different from any valid position.

       === Lexer buffers ===

       type lexbuf = {
	refill_buff : lexbuf -> unit ;

       mutable lex_buffer : string ;

       mutable lex_buffer_len : int ;

       mutable lex_abs_pos : int ;

       mutable lex_start_pos : int ;

       mutable lex_curr_pos : int ;

       mutable lex_last_pos : int ;

       mutable lex_last_action : int ;

       mutable lex_eof_reached : bool ;

       mutable lex_mem : int array ;

       mutable lex_start_p : position ;

       mutable lex_curr_p : position ;
	}

       The type of lexer buffers. A lexer buffer is the argument passed to the scanning functions
       defined by the generated scanners.  The lexer buffer holds the current state of the  scan-
       ner, plus a function to refill the buffer from the input.

       At  each  token,  the  lexing engine will copy lex_curr_p to lex_start_p , then change the
       pos_cnum field of lex_curr_p by updating it with the number of characters read  since  the
       start of the lexbuf .  The other fields are left unchanged by the lexing engine.  In order
       to keep them accurate, they must be initialised before the first use of	the  lexbuf,  and
       updated by the relevant lexer actions (i.e. at each end of line -- see also new_line ).

       val from_channel : Pervasives.in_channel -> lexbuf

       Create  a  lexer  buffer on the given input channel.  Lexing.from_channel inchan returns a
       lexer buffer which reads from the input channel inchan , at the current reading position.

       val from_string : string -> lexbuf

       Create a lexer buffer which reads from the given string. Reading  starts  from  the  first
       character in the string. An end-of-input condition is generated when the end of the string
       is reached.

       val from_function : (string -> int -> int) -> lexbuf

       Create a lexer buffer with the given function as its reading  method.   When  the  scanner
       needs more characters, it will call the given function, giving it a character string s and
       a character count n . The function should put n characters or less  in  s  ,  starting  at
       character  number  0,  and  return  the number of characters provided. A return value of 0
       means end of input.

       === Functions for lexer semantic actions ===

       === The following functions can be called from the semantic actions of  lexer  definitions
       (the  ML  code  enclosed  in braces that computes the value returned by lexing functions).
       They give access to the character string matched by the regular expression associated with
       the semantic action. These functions must be applied to the argument lexbuf, which, in the
       code generated by ocamllex, is bound to the lexer buffer passed to the  parsing	function.
       ===

       val lexeme : lexbuf -> string

       Lexing.lexeme lexbuf returns the string matched by the regular expression.

       val lexeme_char : lexbuf -> int -> char

       Lexing.lexeme_char lexbuf i returns character number i in the matched string.

       val lexeme_start : lexbuf -> int

       Lexing.lexeme_start  lexbuf  returns the offset in the input stream of the first character
       of the matched string.  The first character of the stream has offset 0.

       val lexeme_end : lexbuf -> int

       Lexing.lexeme_end lexbuf returns the offset in the input stream of the character following
       the last character of the matched string. The first character of the stream has offset 0.

       val lexeme_start_p : lexbuf -> position

       Like lexeme_start , but return a complete position instead of an offset.

       val lexeme_end_p : lexbuf -> position

       Like lexeme_end , but return a complete position instead of an offset.

       val new_line : lexbuf -> unit

       Update  the  lex_curr_p	field  of the lexbuf to reflect the start of a new line.  You can
       call this function in the semantic action of the rule that matches the end-of-line charac-
       ter.

       Since 3.11.0

       === Miscellaneous functions ===

       val flush_input : lexbuf -> unit

       Discard	the  contents of the buffer and reset the current position to 0.  The next use of
       the lexbuf will trigger a refill.

OCamldoc				    2014-06-09					Lexing(3)
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