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 file and the beginning of the line); pos_cnum is the offset of the position (number of characters between the beginning of the file and the position).
See the documentation of type lexbuf for information about how the lexing engine will manage positions.
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.
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).
Note: Batteries does not currently support the ~with_positions:false mode available since OCaml 4.08 to disable position tracking. If you need this, please get in touch with the Batteries maintainers.
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.
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.
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.
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.
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.