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 mapi : (int -> char -> char) -> string -> string
String.mapi f s calls f with each character of s and its index (in increasing index order) and stores the results in a new string that is returned.
Since 4.02.0
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
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
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.
val uppercase_ascii : string -> string
Return a copy of the argument, with all lowercase letters translated to uppercase, using the US-ASCII character set.
Since 2.5.0
val lowercase_ascii : string -> string
Return a copy of the argument, with all uppercase letters translated to lowercase, using the US-ASCII character set.
Since 2.5.0
val capitalize_ascii : string -> string
Return a copy of the argument, with the first character set to uppercase, using the US-ASCII character set.
Since 2.5.0
val uncapitalize_ascii : string -> string
Return a copy of the argument, with the first character set to lowercase, using the US-ASCII character set.
Since 2.5.0
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
val to_float : string -> float
Returns the float represented by the given string or
Raises

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_lefti : ('a -> int -> char -> 'a) -> 'a -> string -> 'a
As fold_left, but with the index of the element as additional argument
Since 2.3.0
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 fold_righti : (int -> char -> 'a -> 'a) -> string -> 'a -> 'a
As fold_right, but with the index of the element as additional argument
Since 2.3.0
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
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

val find_all : string -> string -> int BatEnum.t
find_all s x enumerates positions of s at which x occurs. Example: find_all "aabaabaa" "aba" |> List.of_enum will return the list [1; 4].
Since 2.2.0
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_on_char : char -> string -> string list
String.split_on_char sep s returns the list of all (possibly empty) substrings of s that are delimited by the sep character.

The function's output is specified by the following invariants:


Since 2.5.3
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
val edit_distance : t -> t -> int
Edition distance (also known as "Levenshtein distance"). See wikipedia
Since 2.2.0

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.