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.
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
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
String.get s n returns character number n in string s. You can also write s.[n] instead of String.get s n.
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.
String.create n returns a fresh string of length n. The string initially contains arbitrary characters.
String.make n c returns a fresh string of length n, filled with the character c.
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.
String.fill s start len c modifies string s in place, replacing len characters by c, starting at start.
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.
String.concat sep sl concatenates the list of strings sl, inserting the separator string sep between each.
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]; ().
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.
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.
String.index s c returns the character number of the first occurrence of character c in string s.
String.index_opt s c returns the index of the first occurrence of character c in string s, or None if c does not occur in s.
String.rindex s c returns the character number of the last occurrence of character c in string s.
String.rindex_opt s c returns the index of the last occurrence of character c in string s, or None if c does not occur in s.
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.
String.index_from_opt s i c returns the index of the first occurrence of character c in string s after position i or None if c does not occur in s after position i.
String.index_opt s c is equivalent to String.index_from_opt s 0 c. Raise Invalid_argument if i is not a valid position in s.
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.
String.rindex_from_opt s i c returns the index of the last occurrence of character c in string s before position i+1 or None if c does not occur in s before position i+1.
String.rindex_opt s c is equivalent to String.rindex_from_opt s (String.length s - 1) c.
Raise Invalid_argument if i+1 is not a valid position in s.
String.contains s c tests if character c appears in the string s.
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.
String.rcontains_from s stop c tests if character c appears in s before position stop+1.
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.
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.
Return a copy of the argument, with the first character set to uppercase.
Return a copy of the argument, with the first character set to lowercase.
Return a copy of the argument, with all lowercase letters translated to uppercase, using the US-ASCII character set.
Return a copy of the argument, with all uppercase letters translated to lowercase, using the US-ASCII character set.
Return a copy of the argument, with the first character set to uppercase, using the US-ASCII character set.
Return a copy of the argument, with the first character set to lowercase, using the US-ASCII character set.
val enum : string -> char BatEnum.tReturns 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 -> stringCreates a string from a character enumeration. Example: ['f'; 'o'; 'o'] |> List.enum |> String.of_enum = "foo"
val backwards : string -> char BatEnum.tReturns 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 -> stringBuild 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
Converts a list of characters to a string.
Example: ['c'; 'h'; 'a'; 'r'; 's'] |> String.of_list = "chars"
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"
Returns the string representation of an int.
Example: String.of_int 56 = "56" && String.of_int (-1) = "-1"
Returns the string representation of an float.
Example: String.of_float 1.246 = "1.246"
Returns a string containing one given character.
Example: String.of_char 's' = "s"
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" *
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'
As fold_left, but with the index of the element as additional argument
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
As fold_right, but with the index of the element as additional argument
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"
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"
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] ]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.
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.
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.
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.
val find_all : string -> string -> int BatEnum.tfind_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].
ends_with s x returns true if the string s is ending with x, false otherwise.
Example: String.ends_with "foobarbaz" "rbaz" = true
starts_with s x returns true if s is starting with x, false otherwise.
Example: String.starts_with "foobarbaz" "fooz" = false
exists str sub returns true if sub is a substring of str or false otherwise.
Example: String.exists "foobarbaz" "obar" = true
Returns the same string but without the first n characters. By default n is 1. If n is strictly less than zero
Returns the same string but without the last n characters. By default n is 1. If n is strictly less than zero
Returns the same string but with the first l characters on the left and the first r characters on the right removed. By default, l and r are both 1.
chop ~l ~r s is equivalent to lchop ~n:l (rchop ~n:r s).
Returns the same string but without the leading and trailing whitespaces (according to BatChar.is_whitespace).
Example: String.trim " \t foo\n " = "foo"
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.
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"
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"
as left
tail r pos returns the string containing all but the pos first characters of r
Example: String.tail "Weeble" 4 = "le"
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"
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"
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")
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"
repeat s n returns s ^ s ^ ... ^ s
Example: String.repeat "foo" 4 = "foofoofoofoo"
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".
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:
sep as a separator returns a string equal to the input (String.concat (String.make 1 sep)
(String.split_on_char sep s) = s).sep character.split s sep splits the string s between the first occurrence of sep, and returns the two parts before and after the occurrence (excluded).
rsplit s sep splits the string s between the last occurrence of sep, and returns the two parts before and after the occurrence (excluded).
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"; ""]
Same as concat
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 "
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"
explode s returns the list of characters in the string s.
Example: String.explode "foo" = ['f'; 'o'; 'o']
implode cs returns a string resulting from concatenating the characters in the list cs.
Example: String.implode ['b'; 'a'; 'r'] = "bar"
val ord : t -> t -> BatOrd.orderOrdering function for strings, see BatOrd
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"
Compare two strings, case-insensitive.
Example: String.icompare "FOO" "bar" = 1 i.e. "foo" > "bar"
module IString : BatInterfaces.OrderedType with type t = tuses icompare as ordering function
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 = tuses numeric_compare as its ordering function
Edition distance (also known as "Levenshtein distance"). See wikipedia
val print : 'a BatInnerIO.output -> string -> unitPrint a string.
Example: String.print stdout "foo\n"
val println : 'a BatInnerIO.output -> string -> unitPrint a string, end the line.
Example: String.println stdout "foo"
val print_quoted : 'a BatInnerIO.output -> string -> unitPrint 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 ... endExceptionless counterparts for error-raising operations
module Cap : sig ... endCapabilities for strings.