Provided by: ocaml-man_4.08.1-8_all 
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 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.