NAME

       Stdlib.Lexing - no description

Module

       Module   Stdlib.Lexing

Documentation

       Module Lexing
        : (module Stdlib__Lexing)

   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 manage 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 : bytes ;

       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 scanner, plus a function  to  refill
       the buffer from the input.

       Lexers  can optionally maintain the lex_curr_p and lex_start_p position fields.  This "position tracking"
       mode is the default, and it corresponds to passing ~with_position:true to  functions  that  create  lexer
       buffers.  In  this mode, the lexing engine and lexer actions are co-responsible for properly updating the
       position fields, as described in the  next  paragraph.   When  the  mode  is  explicitly  disabled  (with
       ~with_position:false ), the lexing engine will not touch the position fields and the lexer actions should
       be  careful not to do it either; the lex_curr_p and lex_start_p field will then always hold the dummy_pos
       invalid position.  Not tracking positions avoids allocations and  memory  writes  and  can  significantly
       improve the performance of the lexer in contexts where lex_start_p and lex_curr_p are not needed.

       Position  tracking  mode  works  as  follows.   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 : ?with_positions:bool -> 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 : ?with_positions:bool -> 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 : ?with_positions:bool -> (bytes -> 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 byte sequence s and a byte count n . The
       function should put n bytes or fewer in s , starting at index 0, and return the number of bytes provided.
       A return value of 0 means end of input.

       val set_position : lexbuf -> position -> unit

       Set the initial tracked  input  position  for  lexbuf  to  a  custom  value.   Ignores  pos_fname  .  See
       Lexing.set_filename for changing this field.

       Since 4.11

       val set_filename : lexbuf -> string -> unit

       Set filename in the initial tracked position to file in lexbuf .

       Since 4.11

       val with_positions : lexbuf -> bool

       Tell  whether the lexer buffer keeps track of position fields lex_curr_p / lex_start_p , as determined by
       the corresponding optional argument for functions that create lexer buffers (whose default value is  true
       ).

       When  with_positions  is  false , lexer actions should not modify position fields.  Doing it nevertheless
       could re-enable the with_position mode and degrade performances.

   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.  When position tracking is
       disabled, the function returns dummy_pos .

       val lexeme_end_p : lexbuf -> position

       Like lexeme_end , but return a complete position  instead  of  an  offset.   When  position  tracking  is
       disabled, the function returns dummy_pos .

       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 character.  The function does nothing
       when position tracking is disabled.

       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                                           2023-10-26                                  Stdlib.Lexing(3o)