module Lexing: sig .. endThe run-time library for lexers generated by ocamllex.
type position = {
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pos_fname : string; |
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pos_lnum : int; |
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pos_bol : int; |
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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.
type lexbuf = {
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refill_buff : lexbuf -> unit; |
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mutable lex_buffer : bytes; |
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mutable lex_buffer_len : int; |
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mutable lex_abs_pos : int; |
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mutable lex_start_pos : int; |
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mutable lex_curr_pos : int; |
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mutable lex_last_pos : int; |
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mutable lex_last_action : int; |
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mutable lex_eof_reached : bool; |
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mutable lex_mem : int array; |
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mutable lex_start_p : position; |
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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 set_position : lexbuf -> position -> unit
Set the initial tracked input position for lexbuf to a custom value.
Ignores pos_fname. See Lexing.set_filename for changing this field.
val set_filename : lexbuf -> string -> unit
Set filename in the initial tracked position to file in
lexbuf.
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.
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.
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.