package sedlex

  1. Overview
  2. Docs

Runtime support for lexers generated by sedlex.

This module is roughly equivalent to the module Lexing from the OCaml standard library, except that its lexbuffers handle Unicode code points (OCaml type: Uchar.t in the range 0..0x10ffff) instead of bytes (OCaml type: char).

It is possible to have sedlex-generated lexers work on a custom implementation for lex buffers. To do this, define a module L which implements the start, next, mark and backtrack functions (See the Internal Interface section below for a specification). They need not work on a type named lexbuf: you can use the type name you want. Then, just do in your sedlex-processed source, bind this module to the name Sedlexing (for instance, with a local module definition: let module Sedlexing = L in ....

Of course, you'll probably want to define functions like lexeme to be used in the lexers semantic actions.

type lexbuf

The type of lexer buffers. A lexer buffer is the argument passed to the scanning functions defined by the generated lexers. The lexer buffer holds the internal information for the scanners, including the code points of the token currently scanned, its position from the beginning of the input stream, and the current position of the lexer.

exception InvalidCodepoint of int

Raised by some functions to signal that some code point is not compatible with a specified encoding.

exception MalFormed

Raised by functions in the Utf8 and Utf16 modules to report strings which do not comply to the encoding.

Creating generic lexbufs
val create : (Uchar.t array -> int -> int -> int) -> lexbuf

Create a generic lexer buffer. When the lexer needs more characters, it will call the given function, giving it an array of Uchars a, a position pos and a code point count n. The function should put n code points or less in a, starting at position pos, and return the number of characters provided. A return value of 0 means end of input.

val set_position : lexbuf -> Lexing.position -> unit

set the initial tracked input position for lexbuf. If set to Lexing.dummy_pos, Sedlexing will not track position information for you.

val set_filename : lexbuf -> string -> unit

set_filename lexbuf file sets the filename to file in lexbuf. It also sets the Lexing.pos_fname field in returned Lexing.position records.

val from_gen : Uchar.t Gen.t -> lexbuf

Create a lexbuf from a stream of Unicode code points.

val from_stream : Uchar.t Stream.t -> lexbuf

Create a lexbuf from a stream of Unicode code points.

  • deprecated Use [Sedlexing.from_gen] instead.
val from_int_array : int array -> lexbuf

Create a lexbuf from an array of Unicode code points.

val from_uchar_array : Uchar.t array -> lexbuf

Create a lexbuf from an array of Unicode code points.

Interface for lexers semantic actions

The following functions can be called from the semantic actions of lexer definitions. They give access to the character string matched by the regular expression associated with the semantic action.

val lexeme_start : lexbuf -> int

Sedlexing.lexeme_start lexbuf returns the offset in the input stream of the first code point of the matched string. The first code point of the stream has offset 0.

val lexeme_end : lexbuf -> int

Sedlexing.lexeme_end lexbuf returns the offset in the input stream of the character following the last code point of the matched string. The first character of the stream has offset 0.

val loc : lexbuf -> int * int

Sedlexing.loc lexbuf returns the pair (Sedlexing.lexeme_start lexbuf,Sedlexing.lexeme_end lexbuf).

val lexeme_length : lexbuf -> int

Sedlexing.lexeme_length lexbuf returns the difference (Sedlexing.lexeme_end lexbuf) - (Sedlexing.lexeme_start lexbuf), that is, the length (in code points) of the matched string.

val lexing_positions : lexbuf -> Lexing.position * Lexing.position

Sedlexing.lexing_positions lexbuf returns the start and end positions of the current token, using a record of type Lexing.position. This is intended for consumption by parsers like those generated by Menhir.

val new_line : lexbuf -> unit

Sedlexing.new_line lexbuf increments the line count and sets the beginning of line to the current position, as though a newline character had been encountered in the input.

val lexeme : lexbuf -> Uchar.t array

Sedlexing.lexeme lexbuf returns the string matched by the regular expression as an array of Unicode code point.

val lexeme_char : lexbuf -> int -> Uchar.t

Sedlexing.lexeme_char lexbuf pos returns code point number pos in the matched string.

val sub_lexeme : lexbuf -> int -> int -> Uchar.t array

Sedlexing.sub_lexeme lexbuf pos len returns a substring of the string matched by the regular expression as an array of Unicode code point.

val rollback : lexbuf -> unit

Sedlexing.rollback lexbuf puts lexbuf back in its configuration before the last lexeme was matched. It is then possible to use another lexer to parse the same characters again. The other functions above in this section should not be used in the semantic action after a call to Sedlexing.rollback.

Internal interface

These functions are used internally by the lexers. They could be used to write lexers by hand, or with a lexer generator different from sedlex. The lexer buffers have a unique internal slot that can store an integer. They also store a "backtrack" position.

val start : lexbuf -> unit

start t informs the lexer buffer that any code points until the current position can be discarded. The current position become the "start" position as returned by Sedlexing.lexeme_start. Moreover, the internal slot is set to -1 and the backtrack position is set to the current position.

val next : lexbuf -> Uchar.t option

next lexbuf extracts the next code point from the lexer buffer and increments to current position. If the input stream is exhausted, the function returns None. If a '\n' is encountered, the tracked line number is incremented.

val mark : lexbuf -> int -> unit

mark lexbuf i stores the integer i in the internal slot. The backtrack position is set to the current position.

val backtrack : lexbuf -> int

backtrack lexbuf returns the value stored in the internal slot of the buffer, and performs backtracking (the current position is set to the value of the backtrack position).

val with_tokenizer : (lexbuf -> 'token) -> lexbuf -> unit -> 'token * Lexing.position * Lexing.position

with_tokenizer tokenizer lexbuf given a lexer and a lexbuf, returns a generator of tokens annotated with positions. This generator can be used with the Menir parser generator's incremental API.

Support for common encodings
module Latin1 : sig ... end
module Utf8 : sig ... end
module Utf16 : sig ... end

Innovation. Community. Security.