Module B0_std.String

Strings.

String

include module type of Stdlib.String
val length : string -> int

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

val get : string -> int -> char

String.get s n returns the character at index n in string s. You can also write s.[n] instead of String.get s n.

Raise Invalid_argument if n not a valid index in s.

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

String.set s n c modifies byte sequence s in place, replacing the byte at index n with c. You can also write s.[n] <- c instead of String.set s n c.

Raise Invalid_argument if n is not a valid index in s.

deprecated

This is a deprecated alias of Bytes.set.

val create : int -> bytes

String.create n returns a fresh byte sequence of length n. The sequence is uninitialized and contains arbitrary bytes.

Raise Invalid_argument if n < 0 or n > Sys.max_string_length.

deprecated

This is a deprecated alias of Bytes.create.

val make : int -> char -> string

String.make n c returns a fresh string of length n, filled with the character c.

Raise Invalid_argument if n < 0 or n > Sys.max_string_length.

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

String.init n f returns a string of length n, with character i initialized to the result of f i (called in increasing index order).

Raise Invalid_argument if n < 0 or n > Sys.max_string_length.

since
4.02.0
val copy : string -> string

Return a copy of the given string.

deprecated

Because strings are immutable, it doesn't make much sense to make identical copies of them.

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.

Raise Invalid_argument if start and len do not designate a valid substring of s.

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

String.fill s start len c modifies byte sequence s in place, replacing len bytes with c, starting at start.

Raise Invalid_argument if start and len do not designate a valid range of s.

deprecated

This is a deprecated alias of Bytes.fill.

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

Same as Bytes.blit_string.

val concat : string -> string list -> string

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

Raise Invalid_argument if the result is longer than Sys.max_string_length bytes.

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 (in increasing index order) 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 neither 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. All characters outside the ASCII printable range (32..126) are escaped, as well as backslash and double-quote.

If there is no special character in the argument that needs escaping, return the original string itself, not a copy.

Raise Invalid_argument if the result is longer than Sys.max_string_length bytes.

The function Scanf.unescaped is a left inverse of escaped, i.e. Scanf.unescaped (escaped s) = s for any string s (unless escape s fails).

val index : string -> char -> int

String.index s c returns the index of the first occurrence of character c in string s.

Raise Not_found if c does not occur in s.

val index_opt : string -> char -> int option

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.

since
4.05
val rindex : string -> char -> int

String.rindex s c returns the index of the last occurrence of character c in string s.

Raise Not_found if c does not occur in s.

val rindex_opt : string -> char -> int option

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.

since
4.05
val index_from : string -> int -> char -> int

String.index_from s i c returns the index 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.

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

val index_from_opt : string -> int -> char -> int option

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.

since
4.05
val rindex_from : string -> int -> char -> int

String.rindex_from s i c returns the index 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.

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

val rindex_from_opt : string -> int -> char -> int option

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.

since
4.05
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.

Raise 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.

Raise 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.

deprecated

Functions operating on Latin-1 character set are deprecated.

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.

deprecated

Functions operating on Latin-1 character set are deprecated.

val capitalize : string -> string

Return a copy of the argument, with the first character set to uppercase, using the ISO Latin-1 (8859-1) character set..

deprecated

Functions operating on Latin-1 character set are deprecated.

val uncapitalize : string -> string

Return a copy of the argument, with the first character set to lowercase, using the ISO Latin-1 (8859-1) character set..

deprecated

Functions operating on Latin-1 character set are deprecated.

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
4.03.0
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
4.03.0
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
4.03.0
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
4.03.0
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.

val equal : t -> t -> bool

The equal function for strings.

since
4.03.0
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:

  • The list is not empty.
  • Concatenating its elements using sep as a separator returns a string equal to the input (String.concat (String.make 1 sep) (String.split_on_char sep s) = s).
  • No string in the result contains the sep character.
since
4.04.0
Iterators
val to_seq : t -> char Stdlib.Seq.t

Iterate on the string, in increasing index order. Modifications of the string during iteration will be reflected in the iterator.

since
4.07
val to_seqi : t -> (int * char) Stdlib.Seq.t

Iterate on the string, in increasing order, yielding indices along chars

since
4.07
val of_seq : char Stdlib.Seq.t -> t

Create a string from the generator

since
4.07
val empty : string

empty is "".

val head : string -> char option

head s if Some s.[0] if s <> "" and None otherwise.

val of_char : char -> string

of_char c is c as a string.

Predicates

val is_empty : string -> bool

is_empty s is equal empty s.

val is_prefix : affix:string -> string -> bool

is_prefix ~affix s is true iff affix.[i] = s.[i] for all indices i of affix.

val is_infix : affix:string -> string -> bool

is_infix ~affix s is true iff there exists an index j such that for all indices i of affix, affix.[i] = s.[j+ 1].

val is_suffix : affix:string -> string -> bool

is_suffix ~affix s is true iff affix.[i] = s.[m - i] for all indices i of affix and with m = String.length s - 1.

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

for_all p s is true iff for all indices i of s, p s.[i] = true.

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

exists p s is true iff there exists an index i of s with p s.[i] = true.

Extracting substrings

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

with_index_range ~first ~last s are the consecutive bytes of s whose indices exist in the range [first;last].

first defaults to 0 and last to String.length s - 1.

Note that both first and last can be any integer. If first > last the interval is empty and the empty string is returned.

Breaking

Breaking with magnitudes

val take_left : int -> string -> string

take_left n s are the first n bytes of s. This is s if n >= length s and "" if n <= 0.

val take_right : int -> string -> string

take_right n s are the last n bytes of s. This is s if n >= length s and "" if n <= 0.

val drop_left : int -> string -> string

drop_left n s is s without the first n bytes of s. This is "" if n >= length s and s if n <= 0.

val drop_right : int -> string -> string

drop_right n s is s without the last n bytes of s. This is "" if n >= length s and s if n <= 0.

val break_left : int -> string -> string * string

break_left n v is (take_left n v, drop_left n v).

val break_right : int -> string -> string * string

break_right n v is (drop_left n v, take_right n v).

Breaking with predicates

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

keep_left sat s are the first consecutive sat statisfying bytes of s.

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

keep_right sat s are the last consecutive sat satisfying bytes of s.

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

lose_left sat s is s without the first consecutive sat satisfying bytes of s.

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

lose_right sat s is s without the last consecutive sat satisfying bytes of s.

val span_left : (char -> bool) -> string -> string * string

span_left sat s is (keep_left sat s, lose_left sat s).

val span_right : (char -> bool) -> string -> string * string

span_right sat s is (lose_right sat s, keep_right sat s).

Breaking with separators

val cut_left : sep:string -> string -> (string * string) option

cut ~sep s is either the pair Some (l,r) of the two (possibly empty) substrings of s that are delimited by the first match of the separator character sep or None if sep can't be matched in s. Matching starts from the left of s.

The invariant l ^ sep ^ r = s holds.

raises Invalid_argument

if sep is the empty string.

val cut_right : sep:string -> string -> (string * string) option

cut_right ~sep s is like cut_left but matching starts on the right of s.

val cuts_left : ?⁠drop_empty:bool -> sep:string -> string -> string list

cuts_left sep s is the list of all substrings of s that are delimited by matches of the non empty separator string sep. Empty substrings are omitted in the list if drop_empty is true (defaults to false).

Matching separators in s starts from the left of s (rev is false, default) or the end (rev is true). Once one is found, the separator is skipped and matching starts again, that is separator matches can't overlap. If there is no separator match in s, the list [s] is returned.

The following invariants hold:

  • concat ~sep (cuts ~drop_empty:false ~sep s) = s
  • cuts ~drop_empty:false ~sep s <> []
raises Invalid_argument

if sep is the empty string.

val cuts_right : ?⁠drop_empty:bool -> sep:string -> string -> string list

cuts_right sep s is like cuts_left but matching starts on the right of s.

Traversing

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

map f s is s' with s'.[i] = f s.[i] for all indices i of s. f is invoked in increasing index order.

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

mapi f s is s' with s'.[i] = f i s.[i] for all indices i of s. f is invoked in increasing index order.

Formatting

val pp : string Fmt.t

pp ppf s prints s's bytes on ppf.

val dump : string Fmt.t

dump ppf s prints s as a syntactically valid OCaml string on ppf.

Uniqueness

val uniquify : string list -> string list

uniquify ss is ss without duplicates, the list order is preserved.

val unique : exists:(string -> bool) -> string -> (string, string) Stdlib.result

unique ~exist n is n if exists n is false or r = strf "%s~%d" n d with d the smallest integer in [1;1e9] such that exists r is false or an error if there is no such string.

Suggesting

val edit_distance : string -> string -> int

edit_distance s0 s1 is the number of single character edits (insertion, deletion, substitution) that are needed to change s0 into s1.

val suggest : ?⁠dist:int -> string list -> string -> string list

suggest ~dist candidates s are the elements of candidates whose edit distance is the smallest to s and at most at a distance of dist of s (defaults to 2). If multiple results are returned the order of candidates is preserved.

Escaping and unescaping bytes

See also the Converting to printable US-ASCII characters.

XXX. Limitation cannot escape/unescape multiple bytes (e.g. UTF-8 byte sequences). This could be achieved by tweaking the sigs to return integer pairs but that would allocate quite a bit.

val escaper : (char -> int) -> (bytes -> int -> char -> int) -> string -> string

escaper char_len set_char is a byte escaper that given a byte c uses char_len c bytes in the escaped form and uses set_char b i c to set the escaped form for c in b at index i returning the next writable index (no bounds check need to be performed). For any b, c and i the invariant i + char_len c = set_char b i c must hold.

exception Illegal_escape of int

See unescaper.

val unescaper : (string -> int -> int) -> (bytes -> int -> string -> int -> int) -> string -> (string, int) Stdlib.result

unescaper char_len_at set_char is a byte unescaper that uses char_len_at to determine the length of a byte at a given index in the string to unescape and set_char b k s i to set at index k in b the unescaped character read at index i in s; and returns the next readable index in s (no bound check need to be performed). For any b, s, k and i the invariant i + char_len_at s i = set_char b k s i.

Both char_len_at and set_char may raise Illegal_escape i if the given index i has an illegal or truncated escape. The unescaper only uses this exception internally it returns Error i if it found an illegal escape at index i.

Strings as US-ASCII character sequences

module Ascii : sig ... end

US-ASCII string support.

String map and sets

module Set : sig ... end

String sets.

module Map : sig ... end

String maps.