# Module BatString

    module BatString: sig .. end

String operations.

Given a string `s` of length `l`, we call character number in `s` the index of a character in `s`. Indexes start at `0`, and we will call a character number valid in `s` if it falls within the range `[0...l-1]`. A position is the point between two characters or at the beginning or end of the string. We call a position valid in `s` if it falls within the range `[0...l]`. Note that character number `n` is between positions `n` and `n+1`.

Two parameters `start` and `len` are said to designate a valid substring of `s` if `len >= 0` and `start` and `start+len` are valid positions in `s`.

OCaml strings can be modified in place, for instance via the `String.set` and `String.blit` functions described below. This possibility should be used rarely and with much care, however, since both the OCaml compiler and most OCaml libraries share strings as if they were immutable, rather than copying them. In particular, string literals are shared: a single copy of the string is created at program loading time and returned by all evaluations of the string literal. Consider for example:

          # let f () = "foo";;

          val f : unit -> string = <fun>

              # (f ()).[0] <- 'b';;

          -: unit = ()

            # f ();;

          -: string = "boo"

Likewise, many functions from the standard library can return string literals or one of their string arguments. Therefore, the returned strings must not be modified directly. If mutation is absolutely necessary, it should be performed on a fresh copy of the string, as produced by `String.copy`.

This module replaces Stdlib's String module.

If you're going to do a lot of string slicing, BatSubstring might be a useful module to represent slices of strings, as it doesn't allocate new strings on every operation.
Author(s): Xavier Leroy (base library), Nicolas Cannasse, David Teller, Edgar Friendly

    val init : int -> (int -> char) -> string

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

Example: `String.init 256 char_of_int`

    val is_empty : string -> bool

`is_empty s` returns `true` if `s` is the empty string, `false` otherwise.

Usually a tad faster than comparing `s` with `""`.

Example (for some string `s`): `if String.is_empty s then "(Empty)" else s`

    val length : string -> int

Return the length (number of characters) of the given string.

    val get : string -> int -> char

`String.get s n` returns character number `n` in string `s`. You can also write `s.[n]` instead of `String.get s n`.
Raises `Invalid_argument` if `n` not a valid character number in `s`.

    val set : string -> int -> char -> unit

`String.set s n c` modifies string `s` in place, replacing the character number `n` by `c`. You can also write `s.[n] <- c` instead of `String.set s n c`.
Raises `Invalid_argument` if `n` is not a valid character number in `s`.

    val create : int -> string

`String.create n` returns a fresh string of length `n`. The string initially contains arbitrary characters.
Raises `Invalid_argument` if `n < 0` or `n >` `Sys.max_string_length`.

    val make : int -> char -> string

`String.make n c` returns a fresh string of length `n`, filled with the character `c`.
Raises `Invalid_argument` if `n < 0` or `n >` `Sys.max_string_length`.

    val copy : string -> string

Return a copy of the given string.

    val sub : string -> int -> int -> string

`String.sub s start len` returns a fresh string of length `len`, containing the substring of `s` that starts at position `start` and has length `len`.
Raises `Invalid_argument` if `start` and `len` do not designate a valid substring of `s`.

    val fill : string -> int -> int -> char -> unit

`String.fill s start len c` modifies string `s` in place, replacing `len` characters by `c`, starting at `start`.
Raises `Invalid_argument` if `start` and `len` do not designate a valid substring of `s`.

    val blit : string -> int -> string -> int -> int -> unit

`String.blit src srcoff dst dstoff len` copies `len` characters from string `src`, starting at character number `srcoff`, to string `dst`, starting at character number `dstoff`. It works correctly even if `src` and `dst` are the same string, and the source and destination intervals overlap.
Raises `Invalid_argument` if `srcoff` and `len` do not designate a valid substring of `src`, or if `dstoff` and `len` do not designate a valid substring of `dst`.

    val concat : string -> string list -> string

`String.concat sep sl` concatenates the list of strings `sl`, inserting the separator string `sep` between each.

    val iter : (char -> unit) -> string -> unit

`String.iter f s` applies function `f` in turn to all the characters of `s`. It is equivalent to `f s.[0]; f s.[1]; ...; f s.[String.length s - 1]; ()`.

    val iteri : (int -> char -> unit) -> string -> unit

Same as `String.iter`, but the function is applied to the index of the element as first argument (counting from 0), and the character itself as second argument.
Since 4.00.0

    val map : (char -> char) -> string -> string

`String.map f s` applies function `f` in turn to all the characters of `s` and stores the results in a new string that is returned.
Since 4.00.0

    val trim : string -> string

Return a copy of the argument, without leading and trailing whitespace. The characters regarded as whitespace are: `' '`, `'\012'`, `'\n'`, `'\r'`, and `'\t'`. If there is no leading nor trailing whitespace character in the argument, return the original string itself, not a copy.
Since 4.00.0

    val escaped : string -> string

Return a copy of the argument, with special characters represented by escape sequences, following the lexical conventions of OCaml. If there is no special character in the argument, return the original string itself, not a copy. Its inverse function is Scanf.unescaped.

    val index : string -> char -> int

`String.index s c` returns the character number of the first occurrence of character `c` in string `s`.
Raises `Not_found` if `c` does not occur in `s`.

    val rindex : string -> char -> int

`String.rindex s c` returns the character number of the last occurrence of character `c` in string `s`.
Raises `Not_found` if `c` does not occur in `s`.

    val index_from : string -> int -> char -> int

`String.index_from s i c` returns the character number of the first occurrence of character `c` in string `s` after position `i`. `String.index s c` is equivalent to `String.index_from s 0 c`.
Raises

- `Invalid_argument` if `i` is not a valid position in `s`.
- `Not_found` if `c` does not occur in `s` after position `i`.

    val rindex_from : string -> int -> char -> int

`String.rindex_from s i c` returns the character number of the last occurrence of character `c` in string `s` before position `i+1`. `String.rindex s c` is equivalent to `String.rindex_from s (String.length s - 1) c`.
Raises

- `Invalid_argument` if `i+1` is not a valid position in `s`.
- `Not_found` if `c` does not occur in `s` before position `i+1`.

    val contains : string -> char -> bool

`String.contains s c` tests if character `c` appears in the string `s`.

    val contains_from : string -> int -> char -> bool

`String.contains_from s start c` tests if character `c` appears in `s` after position `start`. `String.contains s c` is equivalent to `String.contains_from s 0 c`.
Raises `Invalid_argument` if `start` is not a valid position in `s`.

    val rcontains_from : string -> int -> char -> bool

`String.rcontains_from s stop c` tests if character `c` appears in `s` before position `stop+1`.
Raises `Invalid_argument` if `stop < 0` or `stop+1` is not a valid position in `s`.

    val uppercase : string -> string

Return a copy of the argument, with all lowercase letters translated to uppercase, including accented letters of the ISO Latin-1 (8859-1) character set.

    val lowercase : string -> string

Return a copy of the argument, with all uppercase letters translated to lowercase, including accented letters of the ISO Latin-1 (8859-1) character set.

    val capitalize : string -> string

Return a copy of the argument, with the first character set to uppercase.

    val uncapitalize : string -> string

Return a copy of the argument, with the first character set to lowercase.

    type t = string

An alias for the type of strings.

    val compare : t -> t -> int

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

###### Conversions

    val enum : string -> char BatEnum.t

Returns an enumeration of the characters of a string. The behaviour is unspecified if the string is mutated while it is enumerated.

Examples: `"foo" |> String.enum |> List.of_enum = ['f'; 'o'; 'o']` `String.enum "a b c" // ((<>) ' ') |> String.of_enum = "abc"`

    val of_enum : char BatEnum.t -> string

Creates a string from a character enumeration. Example: `['f'; 'o'; 'o'] |> List.enum |> String.of_enum = "foo"`

    val backwards : string -> char BatEnum.t

Returns an enumeration of the characters of a string, from last to first.

Examples: `"foo" |> String.backwards |> String.of_enum = "oof"` `let rev s = String.backwards s |> String.of_enum`

    val of_backwards : char BatEnum.t -> string

Build a string from an enumeration, starting with last character, ending with first.

Examples: `"foo" |> String.enum |> String.of_backwards = "oof"` `"foo" |> String.backwards |> String.of_backwards = "foo"` `let rev s = String.enum s |> String.of_backwards`

    val of_list : char list -> string

Converts a list of characters to a string.

Example: `['c'; 'h'; 'a'; 'r'; 's'] |> String.of_list = "chars"`

    val to_list : string -> char list

Converts a string to the list of its characters.

Example: `String.to_list "string" |> List.interleave ';' |> String.of_list = "s;t;r;i;n;g"`

    val of_int : int -> string

Returns the string representation of an int.

Example: `String.of_int 56 = "56" && String.of_int (-1) = "-1"`

    val of_float : float -> string

Returns the string representation of an float.

Example: `String.of_float 1.246 = "1.246"`

    val of_char : char -> string

Returns a string containing one given character.

Example: `String.of_char 's' = "s"`

    val to_int : string -> int

Returns the integer represented by the given string or
Raises

- `Failure` if the string does not represent an integer. This follows OCaml's int literal rules, so "0x" prefixes hexadecimal integers, "0o" for octal and "0b" for binary. Underscores within the number are allowed for readability but ignored.

  Examples: `String.to_int "8_480" = String.to_int "0x21_20"` `try ignore(String.to_int "2,3"); false with Failure _ -> true`

- `Failure` if the string does not represent an integer.

    val to_float : string -> float

Returns the float represented by the given string or
Raises

- `Failure` if the string does not represent a float. Decimal points aren't required in the given string, as they are for float literals in OCaml, but otherwise the rules for float literals apply.

  Examples: `String.to_float "12.34e-1" = String.to_float "1.234"` `String.to_float "1" = 1.` `try ignore(String.to_float ""); false with Failure _ -> true`

- `Failure` if the string does not represent a float.

###### String traversals

    val map : (char -> char) -> string -> string

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

Example: `String.map Char.uppercase "Five" = "FIVE"` *

    val fold_left : ('a -> char -> 'a) -> 'a -> string -> 'a

`fold_left f a s` is `f (... (f (f a s.[0]) s.[1]) ...) s.[n-1]`

Examples: `String.fold_left (fun li c -> c::li) [] "foo" = ['o';'o';'f']` `String.fold_left max 'a' "apples" = 's'`

    val fold_right : (char -> 'a -> 'a) -> string -> 'a -> 'a

`fold_right f s b` is `f s.[0] (f s.[1] (... (f s.[n-1] b) ...))`

Examples: `String.fold_right List.cons "foo" [] = ['f';'o';'o']` `String.fold_right (fun c a -> if c = ' ' then a+1 else a) "a b c" 0 = 2`

    val filter : (char -> bool) -> string -> string

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

Example: `String.filter ((<>) ' ') "a b c" = "abc"`

    val filter_map : (char -> char option) -> string -> string

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

Example: `String.filter_map (function 'a'..'z' as c -> Some (Char.uppercase c) | _ -> None) "a b c" = "ABC"`

    val iteri : (int -> char -> unit) -> string -> unit

`String.iteri f s` is equivalent to `f 0 s.[0]; f 1 s.[1]; ...; f len s.[len]` where `len` is length of string `s`. Example:

     let letter_positions word =

          let positions = Array.make 256 [] in

          let count_letter pos c =

            positions.(int_of_char c) <- pos :: positions.(int_of_char c) in

          String.iteri count_letter word;

          Array.mapi (fun c pos -> (char_of_int c, List.rev pos)) positions

          |> Array.to_list

          |> List.filter (fun (c,pos) -> pos <> [])

          in

          letter_positions "hello" = ['e',[1]; 'h',[0]; 'l',[2;3]; 'o',[4] ]

###### Finding

    val find : string -> string -> int

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

Note This implementation is optimized for short strings.
Raises `Not_found` if `x` is not a substring of `s`.

Example: `String.find "foobarbaz" "bar" = 3`

    val find_from : string -> int -> string -> int

`find_from s pos x` behaves as `find s x` but starts searching at position `pos`. `find s x` is equivalent to `find_from s 0 x`.
Raises

- `Not_found` if not substring is found
- `Invalid_argument` if `pos` is not a valid position in the string.

  Example: `String.find_from "foobarbaz" 4 "ba" = 6`

    val rfind : string -> string -> int

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

Note This implementation is optimized for short strings.
Raises `Not_found` if `x` is not a substring of `s`.

Example: `String.rfind "foobarbaz" "ba" = 6`

    val rfind_from : string -> int -> string -> int

`rfind_from s pos x` behaves as `rfind s x` but starts searching from the right at position `pos + 1`. `rfind s x` is equivalent to `rfind_from s (String.length s - 1) x`.

Beware, it search between the beginning of the string to the position `pos + 1`, not between `pos + 1` and the end.
Raises

- `Not_found` if not substring is found
- `Invalid_argument` if `pos` is not a valid position in the string.

  Example: `String.rfind_from "foobarbaz" 6 "ba" = 6`

    val ends_with : string -> string -> bool

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

Example: `String.ends_with "foobarbaz" "rbaz" = true`

    val starts_with : string -> string -> bool

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

Example: `String.starts_with "foobarbaz" "fooz" = false`

    val exists : string -> string -> bool

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

Example: `String.exists "foobarbaz" "obar" = true`

###### Transformations

    val lchop : ?n:int -> string -> string

Returns the same string but without the first `n` characters. By default `n` is 1. If `n` is strictly less than zero
Raises `Invalid_argument.` If the string has `n` or less characters, returns the empty string.

Example: `String.lchop "Weeble" = "eeble"` `String.lchop ~n:3 "Weeble" = "ble"` `String.lchop ~n:1000 "Weeble" = ""`

    val rchop : ?n:int -> string -> string

Returns the same string but without the last `n` characters. By default `n` is 1. If `n` is strictly less than zero
Raises `Invalid_argument.` If the string has `n` or less characters , returns the empty string.

Example: `String.rchop "Weeble" = "Weebl"` `String.rchop ~n:3 "Weeble" = "Wee"` `String.rchop ~n:1000 "Weeble" = ""`

    val trim : string -> string

Returns the same string but without the leading and trailing whitespaces (according to `BatChar.is_whitespace`).

Example: `String.trim " \t foo\n " = "foo"`

    val quote : string -> string

Add quotes around a string and escape any quote or escape appearing in that string. This function is used typically when you need to generate source code from a string.

Examples: `String.quote "foo" = "\"foo\""` `String.quote "\"foo\"" = "\"\\\"foo\\\"\""` `String.quote "\n" = "\"\\n\""` etc.

More precisely, the returned string conforms to the OCaml syntax: if printed, it outputs a representation of the input string as an OCaml string litteral.

    val left : string -> int -> string

`left r len` returns the string containing the `len` first characters of `r`. If `r` contains less than `len` characters, it returns `r`.

Examples: `String.left "Weeble" 4 = "Weeb"` `String.left "Weeble" 0 = ""` `String.left "Weeble" 10 = "Weeble"`

    val right : string -> int -> string

`left r len` returns the string containing the `len` last characters of `r`. If `r` contains less than `len` characters, it returns `r`.

Example: `String.right "Weeble" 4 = "eble"`

    val head : string -> int -> string

as `BatString.left`

    val tail : string -> int -> string

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

Example: `String.tail "Weeble" 4 = "le"`

    val strip : ?chars:string -> string -> string

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

Examples: `String.strip " foo " = "foo"` `String.strip ~chars:" ,()" " boo() bar()" = "boo() bar"`

    val replace_chars : (char -> string) -> string -> string

`replace_chars f s` returns a string where all chars `c` of `s` have been replaced by the string returned by `f c`.

Example: `String.replace_chars (function ' ' -> "(space)" | c -> String.of_char c) "foo bar" = "foo(space)bar"`

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

`replace ~str ~sub ~by` returns a tuple consisting of a boolean and a string where the first occurrence of the string `sub` within `str` has been replaced by the string `by`. The boolean is true if a subtitution has taken place.

Example: `String.replace "foobarbaz" "bar" "rab" = (true, "foorabbaz")`

    val nreplace : str:string -> sub:string -> by:string -> string

`nreplace ~str ~sub ~by` returns a string obtained by iteratively replacing each occurrence of `sub` by `by` in `str`, from right to left. It returns a copy of `str` if `sub` has no occurrence in `str`.

Example: `nreplace ~str:"bar foo aaa bar" ~sub:"aa" ~by:"foo" = "bar foo afoo bar"`

    val repeat : string -> int -> string

`repeat s n` returns `s ^ s ^ ... ^ s`

Example: `String.repeat "foo" 4 = "foofoofoofoo"`

    val rev : string -> string

`string s` returns the reverse of string `s`
Since 2.1

###### In-Place Transformations

    val rev_in_place : string -> unit

`rev_in_place s` mutates the string `s`, so that its new value is the mirror of its old one: for instance if s contained `"Example!"`, after the mutation it will contain `"!elpmaxE"`.

    val in_place_mirror : string -> unit

Deprecated.Use `String.rev_in_place` instead

###### Splitting around

    val split : string -> by:string -> string * string

`split s sep` splits the string `s` between the first occurrence of `sep`, and returns the two parts before and after the occurence (excluded).
Raises `Not_found` if the separator is not found.

Examples: `String.split "abcabcabc" "bc" = ("a","abcabc")` `String.split "abcabcabc" "" = ("","abcabcabc")`

    val rsplit : string -> by:string -> string * string

`rsplit s sep` splits the string `s` between the last occurrence of `sep`, and returns the two parts before and after the occurence (excluded).
Raises `Not_found` if the separator is not found.

Example: `String.rsplit "abcabcabc" "bc" = ("abcabca","")`

    val nsplit : string -> by:string -> string list

`nsplit s sep` splits the string `s` into a list of strings which are separated by `sep` (excluded). `nsplit "" _` returns the empty list.

Example: `String.nsplit "abcabcabc" "bc" = ["a"; "a"; "a"; ""]`

    val join : string -> string list -> string

Same as `BatString.concat`

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

`slice ?first ?last s` returns a "slice" of the string 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 string, 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 string. For example, `slice ~last:(-2) s` will return the string `s`, but without the last two characters.

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

Example: `String.slice ~first:1 ~last:(-3) " foo bar baz" = "foo bar "`

    val splice : string -> int -> int -> string -> string

`String.splice s off len rep` cuts out the section of `s` indicated by `off` and `len` and replaces it by `rep`

Negative indexes are interpreted as counting from the end of the string. If `off+len` is greater than `length s`, the end of the string is used, regardless of the value of `len`.

If `len` is zero or negative, `rep` is inserted at position `off` without replacing any of `s`.

Example: `String.splice "foo bar baz" 3 5 "XXX" = "fooXXXbaz"`

    val explode : string -> char list

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

Example: `String.explode "foo" = ['f'; 'o'; 'o']`

    val implode : char list -> string

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

Example: `String.implode ['b'; 'a'; 'r'] = "bar"`

###### Comparisons

    val equal : t -> t -> bool

String equality

    val ord : t -> t -> BatOrd.order

Ordering function for strings, see `BatOrd`

    val compare : t -> t -> int

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

Example: `String.compare "FOO" "bar" = -1` i.e. "FOO" < "bar"

    val icompare : t -> t -> int

Compare two strings, case-insensitive.

Example: `String.icompare "FOO" "bar" = 1` i.e. "foo" > "bar"

    module IString: BatInterfaces.OrderedType  with type t = t

uses icompare as ordering function

    val numeric_compare : t -> t -> int

Compare two strings, sorting "abc32def" before "abc210abc".

Algorithm: splits both strings into lists of (strings of digits) or (strings of non digits) (`["abc"; "32"; "def"]` and `["abc"; "210"; "abc"]`) Then both lists are compared lexicographically by comparing elements numerically when both are numbers or lexicographically in other cases.

Example: `String.numeric_compare "xx32" "xx210" < 0`

    module NumString: BatInterfaces.OrderedType  with type t = t

uses numeric_compare as its ordering function

###### Boilerplate code

Printing

    val print : 'a BatInnerIO.output -> string -> unit

Print a string.

Example: `String.print stdout "foo\n"`

    val println : 'a BatInnerIO.output -> string -> unit

Print a string, end the line.

Example: `String.println stdout "foo"`

    val print_quoted : 'a BatInnerIO.output -> string -> unit

Print a string, with quotes as added by the `quote` function.

`String.print_quoted stdout "foo"` prints `"foo"` (with the quotes).

`String.print_quoted stdout "\"bar\""` prints `"\"bar\""` (with the quotes).

`String.print_quoted stdout "\n"` prints `"\n"` (not the escaped character, but `'\'` then `'n'`).

    module Exceptionless: sig .. end

Exceptionless counterparts for error-raising operations

    module Cap: sig .. end

Capabilities for strings.