## `lexing`: the run-time library for lexers generated by camllex

### Lexer buffers

    type lexbuf =
      { refill_buff : lexbuf -> unit;
        lex_buffer : string;
        mutable lex_abs_pos : int;
        mutable lex_start_pos : int;
        mutable lex_curr_pos : int;
        mutable lex_last_pos : int;
        mutable lex_last_action : lexbuf -> obj }

  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.

    value create_lexer_channel : in_channel -> lexbuf

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

    value create_lexer_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.

    value create_lexer : (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 camllex, is bound to the lexer buffer passed to the parsing function.

    value get_lexeme : lexbuf -> string

  `get_lexeme lexbuf` returns the string matched by the regular expression.

    value get_lexeme_char : lexbuf -> int -> char

  `get_lexeme_char lexbuf i` returns character number `i` in the matched string.

    value get_lexeme_start : lexbuf -> int

  `get_lexeme_start lexbuf` returns the position in the input stream of the first character of the matched string. The first character of the stream has position 0.

    value get_lexeme_end : lexbuf -> int

  `get_lexeme_end lexbuf` returns the position in the input stream of the character following the last character of the matched string. The first character of the stream has position 0.