Module Base__Import.Lexing

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.

A value of type position, guaranteed to be different from any valid 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).

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.

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.

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.

Lexing.lexeme lexbuf returns the string matched by the regular expression.

Lexing.lexeme_char lexbuf i returns character number i in the matched string.

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.

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

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

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

Discard the contents of the buffer and reset the current position to 0. The next use of the lexbuf will trigger a refill.