Lexing

`sig
type position = {
pos_fname : string;
pos_lnum : int;
pos_bol : int;
pos_cnum : int;
}
val dummy_pos : Lexing.position
type lexbuf = {
refill_buff : Lexing.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 : Lexing.position;
mutable lex_curr_p : Lexing.position;
}
val from_channel :
?with_positions:bool -> Stdlib.in_channel -> Lexing.lexbuf
val from_string : ?with_positions:bool -> string -> Lexing.lexbuf
val from_function :
?with_positions:bool -> (bytes -> int -> int) -> Lexing.lexbuf
val set_position : Lexing.lexbuf -> Lexing.position -> unit
val set_filename : Lexing.lexbuf -> string -> unit
val with_positions : Lexing.lexbuf -> bool
val lexeme : Lexing.lexbuf -> string
val lexeme_char : Lexing.lexbuf -> int -> char
val lexeme_start : Lexing.lexbuf -> int
val lexeme_end : Lexing.lexbuf -> int
val lexeme_start_p : Lexing.lexbuf -> Lexing.position
val lexeme_end_p : Lexing.lexbuf -> Lexing.position
val new_line : Lexing.lexbuf -> unit
val flush_input : Lexing.lexbuf -> unit
val sub_lexeme : Lexing.lexbuf -> int -> int -> string
val sub_lexeme_opt : Lexing.lexbuf -> int -> int -> string option
val sub_lexeme_char : Lexing.lexbuf -> int -> char
val sub_lexeme_char_opt : Lexing.lexbuf -> int -> char option
type lex_tables = {
lex_base : string;
lex_backtrk : string;
lex_default : string;
lex_trans : string;
lex_check : string;
lex_base_code : string;
lex_backtrk_code : string;
lex_default_code : string;
lex_trans_code : string;
lex_check_code : string;
lex_code : string;
}
val engine : Lexing.lex_tables -> int -> Lexing.lexbuf -> int
val new_engine : Lexing.lex_tables -> int -> Lexing.lexbuf -> int
end`