Lexing(3) OCaml library Lexing(3)NAMELexing - The run-time library for lexers generated by ocamllex.
Module
Module LexingDocumentation
Module Lexing
: sig end
The run-time library for lexers generated by ocamllex .
=== 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 lex‐
ing 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 : string ;
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.
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 : Pervasives.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 : 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 : (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 func‐
tion, 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 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 expres‐
sion.
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 off‐
set.
val lexeme_end_p : lexbuf -> position
Like lexeme_end , but return a complete position instead of an offset.
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.
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.
OCamldoc 2013-10-24 Lexing(3)
