# Module BatText

    module BatText: sig .. end

Heavyweight strings ("ropes")

This module implements ropes as described in Boehm, H., Atkinson, R., and Plass, M. 1995. Ropes: an alternative to strings. Softw. Pract. Exper. 25, 12 (Dec. 1995), 1315-1330.

Ropes are an alternative to strings which support efficient operations:

- determining the length of a rope in constant time
- appending or prepending a small rope to an arbitrarily large one in amortized constant time
- concat, substring, insert, remove operations in amortized logarithmic time
- access to and modification of ropes in logarithmic time

Functional nature and persistence

All operations are non-destructive: the original rope is never modified. When a new rope is returned as the result of an operation, it will share as much data as possible with its "parent". For instance, if a rope of length `n` undergoes `m` operations (assume `n >> m`) like set, append or prepend, the modified rope will only require `O(m)` space in addition to that taken by the original one.

However, Rope is an amortized data structure, and its use in a persistent setting can easily degrade its amortized time bounds. It is thus mainly intended to be used ephemerally. In some cases, it is possible to use Rope persistently with the same amortized bounds by explicitly rebalancing ropes to be reused using `balance`. Special care must be taken to avoid calling `balance` too frequently; in the limit, calling `balance` after each modification would defeat the purpose of amortization.

Limitations

The length of ropes is limited to approximately 700 Mb on 32-bit architectures, 220 Gb on 64 bit architectures.
Author(s): Mauricio Fernandez, Yoriyuki Yamagata, The Batteries Included Team

    type t

The type of the rope.

    exception Out_of_bounds

Raised when an operation violates the bounds of the rope.

    exception Invalid_rope

An exception thrown when some operation required a rope and received an unacceptable rope.

    val max_length : int

Maximum length of the rope (number of UTF-8 characters).

###### Creation and conversions

    val empty : t

The empty rope.

    val of_latin1 : string -> t

Constructs a unicode rope from a latin-1 string.

    val of_string : string -> t

`of_string s` returns a rope corresponding to the UTF-8 encoded string `s`.

    val to_string : t -> string

`to_string t` returns a UTF-8 encoded string representing `t`

    val of_uchar : BatUChar.t -> t

`of_uchar c` returns a rope containing exactly character `c`.

    val of_char : char -> t

`of_char c` returns a rope containing exactly Latin-1 character `c`.

    val make : int -> BatUChar.t -> t

`make i c` returns a rope of length `i` consisting of `c` chars; it is similar to String.make

    val join : t -> t list -> t

Same as `BatText.concat`

    val explode : t -> BatUChar.t list

`explode s` returns the list of characters in the rope `s`.

    val implode : BatUChar.t list -> t

`implode cs` returns a rope resulting from concatenating the characters in the list `cs`.

###### Properties

    val is_empty : t -> bool

Returns whether the rope is empty or not.

    val length : t -> int

Returns the length of the rope (`O(1)`). This is number of UTF-8 characters.

    val height : t -> int

Returns the height (depth) of the rope.

    val balance : t -> t

`balance r` returns a balanced copy of the `r` rope. Note that ropes are automatically rebalanced when their height exceeds a given threshold, but `balance` allows to invoke that operation explicity.

###### Operations

    val append : t -> t -> t

`append r u` concatenates the `r` and `u` ropes. In general, it operates in `O(log(min n1 n2))` amortized time. Small ropes are treated specially and can be appended/prepended in amortized `O(1)` time.

    val (^^^) : t -> t -> t

As `BatText.append`

    val append_char : BatUChar.t -> t -> t

`append_char c r` returns a new rope with the `c` character at the end in amortized `O(1)` time.

    val prepend_char : BatUChar.t -> t -> t

`prepend_char c r` returns a new rope with the `c` character at the beginning in amortized `O(1)` time.

    val get : t -> int -> BatUChar.t

`get r n` returns the (n+1)th character from the rope `r`; i.e. `get r 0` returns the first character. Operates in worst-case `O(log size)` time. Raises Out_of_bounds if a character out of bounds is requested.

    val set : t -> int -> BatUChar.t -> t

`set r n c` returns a copy of rope `r` where the (n+1)th character has been set to `c`. See also `BatText.get`. Operates in worst-case `O(log size)` time.

    val sub : t -> int -> int -> t

`sub r m n` returns a sub-rope of `r` containing all characters whose indexes range from `m` to `m + n - 1` (included). Raises Out_of_bounds in the same cases as sub. Operates in worst-case `O(log size)` time.

    val insert : int -> t -> t -> t

`insert n r u` returns a copy of the `u` rope where `r` has been inserted between the characters with index `n` and `n + 1` in the original rope. The length of the new rope is `length u + length r`. Operates in amortized `O(log(size r) + log(size u))` time.

    val remove : int -> int -> t -> t

`remove m n r` returns the rope resulting from deleting the characters with indexes ranging from `m` to `m + n - 1` (included) from the original rope `r`. The length of the new rope is `length r - n`. Operates in amortized `O(log(size r))` time.

    val concat : t -> t list -> t

`concat sep sl` concatenates the list of ropes `sl`, inserting the separator rope `sep` between each.

###### Iteration

    val iter : (BatUChar.t -> unit) -> t -> unit

`iter f r` applies `f` to all the characters in the `r` rope, in order.

    val iteri : ?base:int -> (int -> BatUChar.t -> unit) -> t -> unit

Operates like `iter`, but also passes the index of the character to the given function.

    val range_iter : (BatUChar.t -> unit) -> int -> int -> t -> unit

`rangeiter f m n r` applies `f` to all the characters whose indices `k` satisfy `m` <= `k` < `m + n`. It is thus equivalent to `iter f (sub m n r)`, but does not create an intermediary rope. `rangeiter` operates in worst-case `O(n + log m)` time, which improves on the `O(n log m)` bound from an explicit loop using `get`. Raises Out_of_bounds in the same cases as `sub`.

    val range_iteri : (int -> BatUChar.t -> unit) -> ?base:int -> int -> int -> t -> unit

As `range_iter`, but passes base + index of the character in the subrope defined by next to arguments.

    val fold : ('a -> BatUChar.t -> 'a) -> 'a -> t -> 'a

`Rope.fold f a r` computes `f (... (f (f a r0) r1)...) rN-1` where `rn = Rope.get n r` and `N = length r`.

    val init : int -> (int -> BatUChar.t) -> t

`init l f` returns the rope of length `l` with the chars f 0 , f 1 , f 2 ... f (l-1).

    val map : (BatUChar.t -> BatUChar.t) -> t -> t

`map f s` returns a rope where all characters `c` in `s` have been replaced by `f c`. *

    val filter_map : (BatUChar.t -> BatUChar.t option) -> t -> t

`filter_map f l` calls `(f a0) (f a1).... (f an)` where `a0..an` are the characters of `l`. It returns the list of elements `bi` such as `f ai = Some bi` (when `f` returns `None`, the corresponding element of `l` is discarded).

    val filter : (BatUChar.t -> bool) -> t -> t

`filter f s` returns a copy of rope `s` in which only characters `c` such that `f c = true` remain.

###### Finding

    val index : t -> BatUChar.t -> int

`Rope.index s c` returns the position of the leftmost occurrence of character `c` in rope `s`. Raise `Not_found` if `c` does not occur in `s`.

    val index_from : t -> int -> BatUChar.t -> int

Same as `Rope.index`, but start searching at the character position given as second argument. `Rope.index s c` is equivalent to `Rope.index_from s 0 c`.

    val rindex : t -> BatUChar.t -> int

`Rope.rindex s c` returns the position of the rightmost occurrence of character `c` in rope `s`. Raise `Not_found` if `c` does not occur in `s`.

    val rindex_from : t -> int -> BatUChar.t -> int

Same as `BatText.rindex`, but start searching at the character position given as second argument. `rindex s c` is equivalent to `rindex_from s (length s - 1) c`.

    val contains : t -> BatUChar.t -> bool

`contains s c` tests if character `c` appears in the rope `s`.

    val contains_from : t -> int -> BatUChar.t -> bool

`contains_from s start c` tests if character `c` appears in the subrope of `s` starting from `start` to the end of `s`.
Raises `Invalid_argument` if `start` is not a valid index of `s`.

    val rcontains_from : t -> int -> BatUChar.t -> bool

`rcontains_from s stop c` tests if character `c` appears in the subrope of `s` starting from the beginning of `s` to index `stop`.
Raises `Invalid_argument` if `stop` is not a valid index of `s`.

    val find : t -> t -> int

`find s x` returns the starting index of the first occurrence of rope `x` within rope `s`.

Note This implementation is optimized for short ropes.
Raises `Invalid_rope` if `x` is not a subrope of `s`.

    val find_from : t -> int -> t -> int

`find_from s ofs x` behaves as `find s x` but starts searching at offset `ofs`. `find s x` is equivalent to `find_from s 0 x`.

    val rfind : t -> t -> int

`rfind s x` returns the starting index of the last occurrence of rope `x` within rope `s`.

Note This implementation is optimized for short ropes.
Raises `Invalid_rope` if `x` is not a subrope of `s`.

    val rfind_from : t -> int -> t -> int

`rfind_from s ofs x` behaves as `rfind s x` but starts searching at offset `ofs`. `rfind s x` is equivalent to `rfind_from s (length s - 1) x`.

    val starts_with : t -> t -> bool

`starts_with s x` returns `true` if `s` is starting with `x`, `false` otherwise.

    val ends_with : t -> t -> bool

`ends_with s x` returns `true` if the rope `s` is ending with `x`, `false` otherwise.

    val exists : t -> t -> bool

`exists str sub` returns true if `sub` is a subrope of `str` or false otherwise.

    val left : t -> int -> t

`left r len` returns the rope containing the `len` first characters of `r`

    val right : t -> int -> t

`left r len` returns the rope containing the `len` last characters of `r`

    val head : t -> int -> t

as `BatText.left`

    val tail : t -> int -> t

`tail r pos` returns the rope containing all but the `pos` first characters of `r`

    val strip : ?chars:BatUChar.t list -> t -> t

Returns the rope without the chars if they are at the beginning or at the end of the rope. By default chars are " \t\r\n".

    val lchop : t -> t

Returns the same rope but without the first character. does nothing if the rope is empty.

    val rchop : t -> t

Returns the same rope but without the last character. does nothing if the rope is empty.

    val slice : ?first:int -> ?last:int -> t -> t

`slice ?first ?last s` returns a "slice" of the rope which corresponds to the characters `s.[first]`, `s.[first+1]`, ..., `s[last-1]`. Note that the character at index `last` is not included! If `first` is omitted it defaults to the start of the rope, i.e. index 0, and if `last` is omitted is defaults to point just past the end of `s`, i.e. `length s`. Thus, `slice s` is equivalent to `copy s`.

Negative indexes are interpreted as counting from the end of the rope. For example, `slice ~last:-2 s` will return the rope `s`, but without the last two characters.

This function never raises any exceptions. If the indexes are out of bounds they are automatically clipped.

    val splice : t -> int -> int -> t -> t

`splice s off len rep` returns the rope in which the section of `s` indicated by `off` and `len` has been cut and replaced by `rep`.

Negative indices are interpreted as counting from the end of the string.

    val fill : t -> int -> int -> BatUChar.t -> t

`fill s start len c` returns the rope in which characters number `start` to `start + len - 1` of `s` has been replaced by `c`.
Raises `Invalid_argument` if `start` and `len` do not designate a valid subrope of `s`.

    val blit : t -> int -> t -> int -> int -> t

`blit src srcoff dst dstoff len` returns a copy of `dst` in which `len` characters have been copied from rope `src`, starting at character number `srcoff`, to rope `dst`, starting at character number `dstoff`. It works correctly even if `src` and `dst` are the same rope, and the source and destination chunks overlap.
Raises `Invalid_argument` if `srcoff` and `len` do not designate a valid subrope of `src`, or if `dstoff` and `len` do not designate a valid subrope of `dst`.

    val concat : t -> t list -> t

`concat sep sl` concatenates the list of ropes `sl`, inserting the separator rope `sep` between each.

    val replace : str:t -> sub:t -> by:t -> bool * t

`replace ~str ~sub ~by` returns a tuple constisting of a boolean and a rope where the first occurrence of the rope `sub` within `str` has been replaced by the rope `by`. The boolean is `true` if a substitution has taken place, `false` otherwise.

###### Splitting around

    val split : t -> t -> t * t

`split s sep` splits the rope `s` between the first occurrence of `sep`.
Raises `Invalid_rope` if the separator is not found.

    val rsplit : t -> t -> t * t

`rsplit s sep` splits the rope `s` between the last occurrence of `sep`.
Raises `Invalid_rope` if the separator is not found.

    val nsplit : t -> t -> t list

`nsplit s sep` splits the rope `s` into a list of ropes which are separated by `sep`. `nsplit "" _` returns the empty list.

    val compare : t -> t -> int

The comparison function for ropes, with the same specification as `Pervasives.compare`. Along with the type `t`, this function `compare` allows the module `Rope` to be passed as argument to the functors `Set.Make` and `Map.Make`.

    val print : (t, 'a) BatIO.printer

Prints a rope to the given out_channel

    val read_char : BatIO.input -> BatUChar.t

Read one Unicode char from a UTF-8 encoded input

    val read_text : BatIO.input -> int -> t

Read up to n chars from a UTF-8 encoded input

    val read_line : BatIO.input -> t

Read a line of UTF-8

    val read_all : BatIO.input -> t

Read the whole contents of a UTF-8 encoded input

    val write_char : (BatUChar.t, 'a) BatIO.printer

Write one uchar to a UTF-8 encoded output.

    val write_text : (t, 'a) BatIO.printer

Write a character text onto a UTF-8 encoded output.

    val write_line : (t, 'a) BatIO.printer

Write one line onto a UTF-8 encoded output, followed by a \n.

    val lines_of : BatIO.input -> t BatEnum.t

offer the lines of a UTF-8 encoded input as an enumeration

    val chars_of : BatIO.input -> BatUChar.t BatEnum.t

offer the characters of an UTF-8 encoded input as an enumeration

    val output_text : unit BatIO.output -> t -> unit

Write the text on the given output channel.