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.