- The Unicode Consortium. The Unicode Standard. (latest version)
- Mark Davis. UAX #29 Unicode Text Segmentation. (latest version)
- Andy Heninger. UAX #14 Unicode Line Breaking Algorithm. (latest version)
- Web based ICU break utility.
The type for custom segmenters. See
type boundary = [
The type for boundaries.
`Grapheme_clusterdetermines extended grapheme clusters boundaries according to UAX 29 (corresponds, for most scripts, to user-perceived characters).
`Worddetermines word boundaries according to UAX 29.
`Sentencedetermines sentence boundaries according to UAX 29.
`Line_breakdetermines mandatory line breaks and line break opportunities according to UAX 14.
pp_boundary ppf b prints an unspecified representation of
add s v is:
`Boundaryif there is a boundary at that point in the sequence of characters. The client must then call
uis the next character in the sequence. The client must then call
`Awaitwhen the segmenter is ready to add a new
`Endwas added and all
`Uchar u to add a new character to the sequence to segment and
`End to signal the end of sequence. After adding one of these two values always call
`End is returned.
val mandatory : t -> bool
mandatory s is
true if the last
`Boundary returned by
add was mandatory. This function only makes sense for
`Line_break segmenters or
`Custom segmenters that sport that notion. For other segmenters or if no
`Boundary was returned so far,
true is returned.
copy s is a copy of
s in its current state. Subsequent
s do not affect the copy.
pp_ret ppf v prints an unspecified representation of
val custom : ?mandatory:( 'a -> bool ) -> name:string -> create:( unit -> 'a ) -> copy:( 'a -> 'a ) -> add:( 'a -> [ `Uchar of Uchar.t | `Await | `End ] -> ret ) -> unit -> custom
create ~mandatory ~name ~create ~copy ~add is a custom segmenter.
nameis a name to identify the segmenter.
createis called when the segmenter is created it should return a custom segmenter value.
copyis called with the segmenter value whenever the segmenter is copied. It should return a copy of the segmenter value.
mandatoryis called with the segmenter value to define the result of the
mandatoryfunction. Defaults always returns
addis called with the segmenter value to define the result of the
addvalue. The returned value should respect the semantics of
add. Use the functions
adds error cases.
val err_exp_await : [< ret ] -> 'a
err_exp_await fnd should be used by custom segmenters when the client tries to
`End while the last returned value was not an
val err_ended : [< ret ] -> 'a
err_ended () should be used by custom segmenter when the client tries to
`End was already added.
`Grapheme_cluster segmenter will always consume only a small bounded amount of memory on any text. Other segmenters will also do so on non-degenerate text, but it's possible to feed them with input that will make them buffer an arbitrary amount of characters.
A segmenter is a stateful filter that inputs a sequence of characters and outputs the same sequence except characters are interleaved with
`Boundary values whenever the segmenter detects a boundary.
create returns a new segmenter for a given boundary type:
let words = Uuseg.create `Word
To add characters to the sequence to segment, call
`Uchar _. To end the sequence call
`End. The segmented sequence of characters is returned character by character, interleaved with
`Boundary values at the appropriate places, by the successive calls to
The client and the segmenter must wait on each other to limit internal buffering: each time the client adds to the sequence by calling
`End it must continue to call
`Await until the segmenter returns
`End. In practice this leads to the following kind of control flow:
let rec add acc v = match Uuseg.add words v with | `Uchar u -> add (`Uchar u :: acc) `Await | `Boundary -> add (`B :: acc) `Await | `Await | `End -> acc
For example to segment the sequence <
"a b") to a list of characters interleaved with
`B values on word boundaries we can write:
let uchar = `Uchar (Uchar.of_int u) let seq = [uchar 0x0041; uchar 0x0020; uchar 0x0042] let seq_words = List.rev (add (List.fold_left add  seq) `End)
utf_8_segments seg s is the list of UTF-8 encoded
seg segments of the UTF-8 encoded string
s. This example uses
Uutf to fold over the characters of
s and to encode the characters in a standard OCaml buffer. Note that this function can be derived directly from
let utf_8_segments seg s = let b = Buffer.create 42 in let flush_segment acc = let segment = Buffer.contents b in Buffer.clear b; if segment = "" then acc else segment :: acc in let seg = Uuseg.create (seg :> Uuseg.boundary) in let rec add acc v = match Uuseg.add seg v with | `Uchar u -> Uutf.Buffer.add_utf_8 b u; add acc `Await | `Boundary -> add (flush_segment acc) `Await | `Await -> acc in let rec uchar acc _ = function | `Uchar _ as u -> add acc u | `Malformed _ -> add acc (`Uchar Uutf.u_rep) in List.rev (flush_segment (add (Uutf.String.fold_utf_8 uchar  s) `End))