Module Base.String

An extension of the standard StringLabels. If you open Base, you'll get these extensions in the String module.

type t = string
include Sexpable.S with type t := t
val t_sexp_grammar : Sexp.Private.Raw_grammar.t
val sub : (t, t) Blit.sub
val subo : (t, t) Blit.subo
include Container.S0 with type t := t with type elt = char
type elt = char
val mem : t -> elt -> bool

Checks whether the provided element is there, using equality on elts.

val is_empty : t -> bool
val iter : t -> f:(elt -> unit) -> unit

iter must allow exceptions raised in f to escape, terminating the iteration cleanly. The same holds for all functions below taking an f.

val fold : t -> init:'accum -> f:('accum -> elt -> 'accum) -> 'accum

fold t ~init ~f returns f (... f (f (f init e1) e2) e3 ...) en, where e1..en are the elements of t.

val fold_result : t -> init:'accum -> f:('accum -> elt -> ('accum, 'e) Result.t) -> ('accum, 'e) Result.t

fold_result t ~init ~f is a short-circuiting version of fold that runs in the Result monad. If f returns an Error _, that value is returned without any additional invocations of f.

val fold_until : t -> init:'accum -> f:('accum -> elt -> ('accum, 'final) Base__Container_intf.Export.Continue_or_stop.t) -> finish:('accum -> 'final) -> 'final

fold_until t ~init ~f ~finish is a short-circuiting version of fold. If f returns Stop _ the computation ceases and results in that value. If f returns Continue _, the fold will proceed. If f never returns Stop _, the final result is computed by finish.

Example:

type maybe_negative =
  | Found_negative of int
  | All_nonnegative of { sum : int }

(** [first_neg_or_sum list] returns the first negative number in [list], if any,
    otherwise returns the sum of the list. *)
let first_neg_or_sum =
  List.fold_until ~init:0
    ~f:(fun sum x ->
      if x < 0
      then Stop (Found_negative x)
      else Continue (sum + x))
    ~finish:(fun sum -> All_nonnegative { sum })
;;

let x = first_neg_or_sum [1; 2; 3; 4; 5]
val x : maybe_negative = All_nonnegative {sum = 15}

let y = first_neg_or_sum [1; 2; -3; 4; 5]
val y : maybe_negative = Found_negative -3
val exists : t -> f:(elt -> bool) -> bool

Returns true if and only if there exists an element for which the provided function evaluates to true. This is a short-circuiting operation.

val for_all : t -> f:(elt -> bool) -> bool

Returns true if and only if the provided function evaluates to true for all elements. This is a short-circuiting operation.

val count : t -> f:(elt -> bool) -> int

Returns the number of elements for which the provided function evaluates to true.

val sum : (module Base__Container_intf.Summable with type t = 'sum) -> t -> f:(elt -> 'sum) -> 'sum

Returns the sum of f i for all i in the container.

val find : t -> f:(elt -> bool) -> elt option

Returns as an option the first element for which f evaluates to true.

val find_map : t -> f:(elt -> 'a option) -> 'a option

Returns the first evaluation of f that returns Some, and returns None if there is no such element.

val to_list : t -> elt list
val to_array : t -> elt array
val min_elt : t -> compare:(elt -> elt -> int) -> elt option

Returns a min (resp. max) element from the collection using the provided compare function. In case of a tie, the first element encountered while traversing the collection is returned. The implementation uses fold so it has the same complexity as fold. Returns None iff the collection is empty.

val max_elt : t -> compare:(elt -> elt -> int) -> elt option
include Identifiable.S with type t := t
val hash_fold_t : Hash.state -> t -> Hash.state
include Sexpable.S with type t := t
val t_of_sexp : Sexplib0.Sexp.t -> t
val sexp_of_t : t -> Sexplib0.Sexp.t
include Stringable.S with type t := t
val of_string : string -> t
val to_string : t -> string
include Comparable.S with type t := t
include Comparisons.S with type t := t
include Comparisons.Infix with type t := t
val (>=) : t -> t -> bool
val (<=) : t -> t -> bool
val (=) : t -> t -> bool
val (>) : t -> t -> bool
val (<) : t -> t -> bool
val (<>) : t -> t -> bool
val compare : t -> t -> int

compare t1 t2 returns 0 if t1 is equal to t2, a negative integer if t1 is less than t2, and a positive integer if t1 is greater than t2.

val min : t -> t -> t
val max : t -> t -> t
val ascending : t -> t -> int

ascending is identical to compare. descending x y = ascending y x. These are intended to be mnemonic when used like List.sort ~compare:ascending and List.sort ~cmp:descending, since they cause the list to be sorted in ascending or descending order, respectively.

val descending : t -> t -> int
val between : t -> low:t -> high:t -> bool

between t ~low ~high means low <= t <= high

val clamp_exn : t -> min:t -> max:t -> t

clamp_exn t ~min ~max returns t', the closest value to t such that between t' ~low:min ~high:max is true.

Raises if not (min <= max).

val clamp : t -> min:t -> max:t -> t Or_error.t
include Comparator.S with type t := t
type comparator_witness
val validate_lbound : min:t Maybe_bound.t -> t Validate.check
val validate_ubound : max:t Maybe_bound.t -> t Validate.check
val validate_bound : min:t Maybe_bound.t -> max:t Maybe_bound.t -> t Validate.check
include Pretty_printer.S with type t := t
val pp : Formatter.t -> t -> unit
include Invariant.S with type t := t
val invariant : t -> unit
val max_length : int

Maximum length of a string.

val length : t -> int
val get : t -> int -> char
val unsafe_get : string -> int -> char

unsafe_get t i is like get t i but does not perform bounds checking. The caller must ensure that it is a memory-safe operation.

val make : int -> char -> t
val copy : t -> t

Assuming you haven't passed -unsafe-string to the compiler, strings are immutable, so there'd be no motivation to make a copy.

val init : int -> f:(int -> char) -> t
val (^) : t -> t -> t

String append. Also available unqualified, but re-exported here for documentation purposes.

Note that a ^ b must copy both a and b into a newly-allocated result string, so a ^ b ^ c ^ ... ^ z is quadratic in the number of strings. String.concat does not have this problem -- it allocates the result buffer only once.

val concat : ?sep:t -> t list -> t

Concatenates all strings in the list using separator sep (with a default separator "").

val escaped : t -> t

Special characters are represented by escape sequences, following the lexical conventions of OCaml.

val contains : ?pos:int -> ?len:int -> t -> char -> bool
val uppercase : t -> t

Operates on the whole string using the US-ASCII character set, e.g. uppercase "foo" = "FOO".

val lowercase : t -> t
val capitalize : t -> t

Operates on just the first character using the US-ASCII character set, e.g. capitalize "foo" = "Foo".

val uncapitalize : t -> t

index gives the index of the first appearance of char in the string when searching from left to right, or None if it's not found. rindex does the same but searches from the right.

For example, String.index "Foo" 'o' is Some 1 while String.rindex "Foo" 'o' is Some 2.

The _exn versions return the actual index (instead of an option) when char is found, and throw an exception otherwise.

module Caseless : sig ... end

Caseless compares and hashes strings ignoring case, so that for example Caseless.equal "OCaml" "ocaml" and Caseless.("apple" < "Banana") are true.

val index : t -> char -> int option

index_exn and index_from_exn raise Caml.Not_found or Not_found_s when char cannot be found in s.

val index_exn : t -> char -> int
val index_from : t -> int -> char -> int option
val index_from_exn : t -> int -> char -> int
val rindex : t -> char -> int option

rindex_exn and rindex_from_exn raise Caml.Not_found or Not_found_s when char cannot be found in s.

val rindex_exn : t -> char -> int
val rindex_from : t -> int -> char -> int option
val rindex_from_exn : t -> int -> char -> int
module Search_pattern : sig ... end

Substring search and replace functions. They use the Knuth-Morris-Pratt algorithm (KMP) under the hood.

val substr_index : ?pos:int -> t -> pattern:t -> int option

Substring search and replace convenience functions. They call Search_pattern.create and then forget the preprocessed pattern when the search is complete. pos < 0 or pos >= length t result in no match (hence substr_index returns None and substr_index_exn raises). may_overlap indicates whether to report overlapping matches, see Search_pattern.index_all.

val substr_index_exn : ?pos:int -> t -> pattern:t -> int
val substr_index_all : t -> may_overlap:bool -> pattern:t -> int list
val substr_replace_first : ?pos:int -> t -> pattern:t -> with_:t -> t
val substr_replace_all : t -> pattern:t -> with_:t -> t

As with Search_pattern.replace_all, the result may still contain pattern.

val is_substring : t -> substring:t -> bool

is_substring ~substring:"bar" "foo bar baz" is true.

val is_substring_at : t -> pos:int -> substring:t -> bool

is_substring_at "foo bar baz" ~pos:4 ~substring:"bar" is true.

val to_list_rev : t -> char list

Returns the reversed list of characters contained in a list.

val rev : t -> t

rev t returns t in reverse order.

val is_suffix : t -> suffix:t -> bool

is_suffix s ~suffix returns true if s ends with suffix.

val is_prefix : t -> prefix:t -> bool

is_prefix s ~prefix returns true if s starts with prefix.

val lsplit2_exn : t -> on:char -> t * t

If the string s contains the character on, then lsplit2_exn s ~on returns a pair containing s split around the first appearance of on (from the left). Raises Caml.Not_found or Not_found_s when on cannot be found in s.

val rsplit2_exn : t -> on:char -> t * t

If the string s contains the character on, then rsplit2_exn s ~on returns a pair containing s split around the first appearance of on (from the right). Raises Caml.Not_found or Not_found_s when on cannot be found in s.

val lsplit2 : t -> on:char -> (t * t) option

lsplit2 s ~on optionally returns s split into two strings around the first appearance of on from the left.

val rsplit2 : t -> on:char -> (t * t) option

rsplit2 s ~on optionally returns s split into two strings around the first appearance of on from the right.

val split : t -> on:char -> t list

split s ~on returns a list of substrings of s that are separated by on. Consecutive on characters will cause multiple empty strings in the result. Splitting the empty string returns a list of the empty string, not the empty list.

val split_on_chars : t -> on:char list -> t list

split_on_chars s ~on returns a list of all substrings of s that are separated by one of the chars from on. on are not grouped. So a grouping of on in the source string will produce multiple empty string splits in the result.

val split_lines : t -> t list

split_lines t returns the list of lines that comprise t. The lines do not include the trailing "\n" or "\r\n".

val lfindi : ?pos:int -> t -> f:(int -> char -> bool) -> int option

lfindi ?pos t ~f returns the smallest i >= pos such that f i t.[i], if there is such an i. By default, pos = 0.

val rfindi : ?pos:int -> t -> f:(int -> char -> bool) -> int option

rfindi ?pos t ~f returns the largest i <= pos such that f i t.[i], if there is such an i. By default pos = length t - 1.

val lstrip : ?drop:(char -> bool) -> t -> t

lstrip ?drop s returns a string with consecutive chars satisfying drop (by default white space, e.g. tabs, spaces, newlines, and carriage returns) stripped from the beginning of s.

val rstrip : ?drop:(char -> bool) -> t -> t

rstrip ?drop s returns a string with consecutive chars satisfying drop (by default white space, e.g. tabs, spaces, newlines, and carriage returns) stripped from the end of s.

val strip : ?drop:(char -> bool) -> t -> t

strip ?drop s returns a string with consecutive chars satisfying drop (by default white space, e.g. tabs, spaces, newlines, and carriage returns) stripped from the beginning and end of s.

val map : t -> f:(char -> char) -> t
val mapi : t -> f:(int -> char -> char) -> t

Like map, but passes each character's index to f along with the char.

val foldi : t -> init:'a -> f:(int -> 'a -> char -> 'a) -> 'a

foldi works similarly to fold, but also passes the index of each character to f.

val concat_map : ?sep:t -> t -> f:(char -> t) -> t

Like map, but allows the replacement of a single character with zero or two or more characters.

val filter : t -> f:(char -> bool) -> t

filter s ~f:predicate discards characters not satisfying predicate.

val tr : target:char -> replacement:char -> t -> t

tr ~target ~replacement s replaces every instance of target in s with replacement.

val tr_multi : target:t -> replacement:t -> (t -> t) Staged.t

tr_multi ~target ~replacement returns a function that replaces every instance of a character in target with the corresponding character in replacement.

If replacement is shorter than target, it is lengthened by repeating its last character. Empty replacement is illegal unless target also is.

If target contains multiple copies of the same character, the last corresponding replacement character is used. Note that character ranges are not supported, so ~target:"a-z" means the literal characters 'a', '-', and 'z'.

val chop_suffix_exn : t -> suffix:t -> t

chop_suffix_exn s ~suffix returns s without the trailing suffix, raising Invalid_argument if suffix is not a suffix of s.

val chop_prefix_exn : t -> prefix:t -> t

chop_prefix_exn s ~prefix returns s without the leading prefix, raising Invalid_argument if prefix is not a prefix of s.

val chop_suffix : t -> suffix:t -> t option
val chop_prefix : t -> prefix:t -> t option
val chop_suffix_if_exists : t -> suffix:t -> t

chop_suffix_if_exists s ~suffix returns s without the trailing suffix, or just s if suffix isn't a suffix of s.

Equivalent to chop_suffix s ~suffix |> Option.value ~default:s, but avoids allocating the intermediate option.

val chop_prefix_if_exists : t -> prefix:t -> t

chop_prefix_if_exists s ~prefix returns s without the leading prefix, or just s if prefix isn't a prefix of s.

Equivalent to chop_prefix s ~prefix |> Option.value ~default:s, but avoids allocating the intermediate option.

val suffix : t -> int -> t

suffix s n returns the longest suffix of s of length less than or equal to n.

val prefix : t -> int -> t

prefix s n returns the longest prefix of s of length less than or equal to n.

val drop_suffix : t -> int -> t

drop_suffix s n drops the longest suffix of s of length less than or equal to n.

val drop_prefix : t -> int -> t

drop_prefix s n drops the longest prefix of s of length less than or equal to n.

val concat_array : ?sep:t -> t array -> t

concat_array sep ar like String.concat, but operates on arrays.

val hash : t -> int

Slightly faster hash function on strings.

val equal : t -> t -> bool

Fast equality function on strings, doesn't use compare_val.

val of_char : char -> t
val of_char_list : char list -> t
module Escaping : sig ... end

Operations for escaping and unescaping strings, with parameterized escape and escapeworthy characters. Escaping/unescaping using this module is more efficient than using Pcre. Benchmark code can be found in core/benchmarks/string_escaping.ml.