containers
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Basic String Utils (Labeled version of CCString)

type 'a iter = ('a -> unit) -> unit

Fast internal iterator.

  • since 2.8
type 'a gen = unit -> 'a option

Strings

type t = string

The type for strings.

val make : int -> char -> string

make n c is a string of length n with each index holding the character c.

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

init n ~f is a string of length n with index i holding the character f i (called in increasing index order).

  • since 4.02.0
val empty : string

The empty string.

  • since 4.13.0
val of_bytes : bytes -> string

Return a new string that contains the same bytes as the given byte sequence.

  • since 4.13.0
val to_bytes : string -> bytes

Return a new byte sequence that contains the same bytes as the given string.

  • since 4.13.0
val get : string -> int -> char

get s i is the character at index i in s. This is the same as writing s.[i].

  • raises Invalid_argument

    if i not an index of s.

Concatenating

Note. The Stdlib.(^) binary operator concatenates two strings.

val concat : sep:string -> string list -> string

concat ~sep ss concatenates the list of strings ss, inserting the separator string sep between each.

val cat : string -> string -> string

cat s1 s2 concatenates s1 and s2 (s1 ^ s2).

  • since 4.13.0

Predicates and comparisons

val starts_with : prefix:string -> string -> bool

starts_with ~prefix s is true if and only if s starts with prefix.

  • since 4.13.0
val ends_with : suffix:string -> string -> bool

ends_with ~suffix s is true if and only if s ends with suffix.

  • since 4.13.0
val contains_from : string -> int -> char -> bool

contains_from s start c is true if and only if c appears in s after position start.

  • raises Invalid_argument

    if start is not a valid position in s.

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

rcontains_from s stop c is true if and only if 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 contains : string -> char -> bool

contains s c is String.contains_from s 0 c.

Extracting substrings

val sub : string -> pos:int -> len:int -> string

sub s ~pos ~len is a string of length len, containing the substring of s that starts at position pos and has length len.

  • raises Invalid_argument

    if pos and len do not designate a valid substring of s.

Transforming

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

map f s is the string resulting from applying f to all the characters of s in increasing order.

  • since 4.00.0
val mapi : f:(int -> char -> char) -> string -> string

mapi ~f s is like map but the index of the character is also passed to f.

  • since 4.02.0
val fold_left : f:('a -> char -> 'a) -> init:'a -> string -> 'a

fold_left f x s computes f (... (f (f x s.[0]) s.[1]) ...) s.[n-1], where n is the length of the string s.

  • since 4.13.0
val fold_right : f:(char -> 'a -> 'a) -> string -> init:'a -> 'a

fold_right f s x computes f s.[0] (f s.[1] ( ... (f s.[n-1] x) ...)), where n is the length of the string s.

  • since 4.13.0
val trim : string -> string

trim s is s without leading and trailing whitespace. Whitespace characters are: ' ', '\x0C' (form feed), '\n', '\r', and '\t'.

  • since 4.00.0
val escaped : string -> string

escaped s is s with special characters represented by escape sequences, following the lexical conventions of OCaml.

All characters outside the US-ASCII printable range [0x20;0x7E] are escaped, as well as backslash (0x2F) and double-quote (0x22).

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

Traversing

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

iteri is like iter, but the function is also given the corresponding character index.

  • since 4.00.0

Searching

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

index_from s i c is the index of the first occurrence of c in s after position i.

  • raises Not_found

    if c does not occur in s after position i.

  • raises Invalid_argument

    if i is not a valid position in s.

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

index_from_opt s i c is the index of the first occurrence of c in s after position i (if any).

  • raises Invalid_argument

    if i is not a valid position in s.

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

rindex_from s i c is the index of the last occurrence of c in s before position i+1.

  • raises Not_found

    if c does not occur in s before position i+1.

  • raises Invalid_argument

    if i+1 is not a valid position in s.

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

rindex_from_opt s i c is the index of the last occurrence of c in s before position i+1 (if any).

  • raises Invalid_argument

    if i+1 is not a valid position in s.

  • since 4.05
val index : string -> char -> int

index s c is String.index_from s 0 c.

val index_opt : string -> char -> int option

index_opt s c is String.index_from_opt s 0 c.

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

rindex s c is String.rindex_from s (length s - 1) c.

val rindex_opt : string -> char -> int option

rindex_opt s c is String.rindex_from_opt s (length s - 1) c.

  • since 4.05

Strings and Sequences

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

to_seqi s is like to_seq but also tuples the corresponding index.

  • since 4.07

UTF decoding and validations

  • since 4.14

UTF-8

val get_utf_8_uchar : t -> int -> Uchar.utf_decode

get_utf_8_uchar b i decodes an UTF-8 character at index i in b.

val is_valid_utf_8 : t -> bool

is_valid_utf_8 b is true if and only if b contains valid UTF-8 data.

UTF-16BE

val get_utf_16be_uchar : t -> int -> Uchar.utf_decode

get_utf_16be_uchar b i decodes an UTF-16BE character at index i in b.

val is_valid_utf_16be : t -> bool

is_valid_utf_16be b is true if and only if b contains valid UTF-16BE data.

UTF-16LE

val get_utf_16le_uchar : t -> int -> Uchar.utf_decode

get_utf_16le_uchar b i decodes an UTF-16LE character at index i in b.

val is_valid_utf_16le : t -> bool

is_valid_utf_16le b is true if and only if b contains valid UTF-16LE data.

Binary decoding of integers

The functions in this section binary decode integers from strings.

All following functions raise Invalid_argument if the characters needed at index i to decode the integer are not available.

Little-endian (resp. big-endian) encoding means that least (resp. most) significant bytes are stored first. Big-endian is also known as network byte order. Native-endian encoding is either little-endian or big-endian depending on Sys.big_endian.

32-bit and 64-bit integers are represented by the int32 and int64 types, which can be interpreted either as signed or unsigned numbers.

8-bit and 16-bit integers are represented by the int type, which has more bits than the binary encoding. These extra bits are sign-extended (or zero-extended) for functions which decode 8-bit or 16-bit integers and represented them with int values.

val get_uint8 : string -> int -> int

get_uint8 b i is b's unsigned 8-bit integer starting at character index i.

  • since 4.13.0
val get_int8 : string -> int -> int

get_int8 b i is b's signed 8-bit integer starting at character index i.

  • since 4.13.0
val get_uint16_ne : string -> int -> int

get_uint16_ne b i is b's native-endian unsigned 16-bit integer starting at character index i.

  • since 4.13.0
val get_uint16_be : string -> int -> int

get_uint16_be b i is b's big-endian unsigned 16-bit integer starting at character index i.

  • since 4.13.0
val get_uint16_le : string -> int -> int

get_uint16_le b i is b's little-endian unsigned 16-bit integer starting at character index i.

  • since 4.13.0
val get_int16_ne : string -> int -> int

get_int16_ne b i is b's native-endian signed 16-bit integer starting at character index i.

  • since 4.13.0
val get_int16_be : string -> int -> int

get_int16_be b i is b's big-endian signed 16-bit integer starting at character index i.

  • since 4.13.0
val get_int16_le : string -> int -> int

get_int16_le b i is b's little-endian signed 16-bit integer starting at character index i.

  • since 4.13.0
val get_int32_ne : string -> int -> int32

get_int32_ne b i is b's native-endian 32-bit integer starting at character index i.

  • since 4.13.0
val seeded_hash : int -> t -> int

A seeded hash function for strings, with the same output value as Hashtbl.seeded_hash. This function allows this module to be passed as argument to the functor Hashtbl.MakeSeeded.

  • since 5.0.0
val get_int32_be : string -> int -> int32

get_int32_be b i is b's big-endian 32-bit integer starting at character index i.

  • since 4.13.0
val get_int32_le : string -> int -> int32

get_int32_le b i is b's little-endian 32-bit integer starting at character index i.

  • since 4.13.0
val get_int64_ne : string -> int -> int64

get_int64_ne b i is b's native-endian 64-bit integer starting at character index i.

  • since 4.13.0
val get_int64_be : string -> int -> int64

get_int64_be b i is b's big-endian 64-bit integer starting at character index i.

  • since 4.13.0
val get_int64_le : string -> int -> int64

get_int64_le b i is b's little-endian 64-bit integer starting at character index i.

  • since 4.13.0
val length : t -> int

length s returns the length (number of characters) of the given string s.

val blit : src:t -> src_pos:int -> dst:Bytes.t -> dst_pos:int -> len:int -> unit

blit ~src ~src_pos ~dst ~dst_pos ~len copies len characters from string src starting at character indice src_pos, to the Bytes sequence dst starting at character indice dst_pos. Like String.blit. Compatible with the -safe-string option.

  • raises Invalid_argument

    if indices are not valid.

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

fold ~f ~init s folds on chars by increasing index. Computes f(… (f (f init s.[0]) s.[1]) …) s.[n-1].

  • since 0.7
val foldi : f:('a -> int -> char -> 'a) -> 'a -> t -> 'a

foldi ~f init s is just like fold, but it also passes in the index of each chars as second argument to the folded function f.

  • since 3.3

Conversions

val to_gen : t -> char gen

to_gen s returns the gen of characters contained in the string s.

val to_iter : t -> char iter

to_iter s returns the iter of characters contained in the string s.

  • since 2.8
val to_seq : t -> char Seq.t

to_seq s returns the Seq.t of characters contained in the string s. Renamed from to std_seq since 3.0.

  • since 3.0
val to_list : t -> char list

to_list s returns the list of characters contained in the string s.

val pp_buf : Buffer.t -> t -> unit

pp_buf buf s prints s to the buffer buf. Renamed from pp since 2.0.

val pp : Format.formatter -> t -> unit

pp f s prints the string s within quotes to the formatter f. Renamed from print since 2.0.

Strings

val equal : string -> string -> bool

equal s1 s2 returns true iff the strings s1 and s2 are equal.

val compare : string -> string -> int

compare s1 s2 compares the strings s1 and s2 and returns an integer that indicates their relative position in the sort order.

val is_empty : string -> bool

is_empty s returns true iff s is empty (i.e. its length is 0).

  • since 1.5
val hash : string -> int

hash s returns the hash value of s.

val rev : string -> string

rev s returns the reverse of s.

  • since 0.17
val pad : ?side:[ `Left | `Right ] -> ?c:char -> int -> string -> string

pad ?side ?c n s ensures that the string s is at least n bytes long, and pads it on the side with c if it's not the case.

  • parameter side

    determines where padding occurs (default: `Left).

  • parameter c

    the char used to pad (default: ' ').

  • since 0.17
val of_char : char -> string

of_char 'a' is "a".

  • since 0.19
val of_gen : char gen -> string

of_gen gen converts a gen of characters to a string.

val of_iter : char iter -> string

of_iter iter converts an iter of characters to a string.

  • since 2.8
val of_seq : char Seq.t -> string

of_seq seq converts a seq of characters to a string. Renamed from of_std_seq since 3.0.

  • since 3.0
val of_list : char list -> string

of_list lc converts a list of characters lc to a string.

val of_array : char array -> string

of_array ac converts an array of characters ac to a string.

val to_array : string -> char array

to_array s returns the array of characters contained in the string s.

val find : ?start:int -> sub:string -> string -> int

find ?start ~sub s returns the starting index of the first occurrence of sub within s or -1.

  • parameter start

    starting position in s.

val find_all : ?start:int -> sub:string -> string -> int gen

find_all ?start ~sub s finds all occurrences of sub in s, even overlapping instances and returns them in a generator gen.

  • parameter start

    starting position in s.

  • since 0.17
val find_all_l : ?start:int -> sub:string -> string -> int list

find_all_l ?start ~sub s finds all occurrences of sub in s and returns them in a list.

  • parameter start

    starting position in s.

  • since 0.17
val mem : ?start:int -> sub:string -> string -> bool

mem ?start ~sub s is true iff sub is a substring of s.

  • since 0.12
val rfind : sub:string -> string -> int

rfind ~sub s finds sub in string s from the right, returns its first index or -1. Should only be used with very small sub.

  • since 0.12
val replace : ?which:[ `Left | `Right | `All ] -> sub:string -> by:string -> string -> string

replace ?which ~sub ~by s replaces some occurrences of sub by by in s.

  • parameter which

    decides whether the occurrences to replace are:

    • `Left first occurrence from the left (beginning).
    • `Right first occurrence from the right (end).
    • `All all occurrences (default).
  • raises Invalid_argument

    if sub = "".

  • since 0.14
val is_sub : sub:string -> sub_pos:int -> string -> pos:int -> sub_len:int -> bool

is_sub ~sub ~sub_pos s ~pos ~sub_len returns true iff the substring of sub starting at position sub_pos and of length sub_len is a substring of s starting at position pos.

val repeat : string -> int -> string

repeat s n creates a string by repeating the string s n times.

val prefix : pre:string -> string -> bool

prefix ~pre s returns true iff pre is a prefix of s.

val suffix : suf:string -> string -> bool

suffix ~suf s returns true iff suf is a suffix of s.

  • since 0.7
val chop_prefix : pre:string -> string -> string option

chop_prefix ~pre s removes pre from s if pre really is a prefix of s, returns None otherwise.

  • since 0.17
val chop_suffix : suf:string -> string -> string option

chop_suffix ~suf s removes suf from s if suf really is a suffix of s, returns None otherwise.

  • since 0.17
val take : int -> string -> string

take n s keeps only the n first chars of s.

  • since 0.17
val drop : int -> string -> string

drop n s removes the n first chars of s.

  • since 0.17
val take_drop : int -> string -> string * string

take_drop n s is take n s, drop n s.

  • since 0.17
val lines : string -> string list

lines s returns a list of the lines of s (splits along '\n').

  • since 0.10
val lines_gen : string -> string gen

lines_gen s returns a generator gen of the lines of s (splits along '\n').

  • since 0.10
val lines_iter : string -> string iter

lines_iter s returns the iter of the lines of s (splits along '\n').

  • since 3.2
val lines_seq : string -> string Seq.t

lines_seq s returns the Seq.t of the lines of s (splits along '\n').

  • since 3.2
val concat_iter : sep:string -> string iter -> string

concat_iter ~sep iter concatenates all strings of iter, separated with sep.

  • since 3.2
val concat_gen : sep:string -> string gen -> string

concat_gen ~sep gen concatenates all strings of gen, separated with sep.

  • since 0.10
val concat_seq : sep:string -> string Seq.t -> string

concat_seq ~sep seq concatenates all strings of seq, separated with sep.

  • since 3.2
val unlines : string list -> string

unlines ls concatenates all strings of ls, separated with '\n'.

  • since 0.10
val unlines_gen : string gen -> string

unlines_gen gen concatenates all strings of gen, separated with '\n'.

  • since 0.10
val unlines_iter : string iter -> string

unlines_iter iter concatenates all strings of iter, separated with '\n'.

  • since 3.2
val unlines_seq : string Seq.t -> string

unlines_seq seq concatenates all strings of seq, separated with '\n'.

  • since 3.2
val set : string -> int -> char -> string

set s i c creates a new string which is a copy of s, except for index i, which becomes c.

  • raises Invalid_argument

    if i is an invalid index.

  • since 0.12
val iter : f:(char -> unit) -> string -> unit

iter ~f s applies function f on each character of s. Alias to String.iter.

  • since 0.12
val filter_map : f:(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).

  • since 0.17
val filter : f:(char -> bool) -> string -> string

filter ~f s discards characters of s not satisfying f.

  • since 0.17
val uniq : eq:(char -> char -> bool) -> string -> string

uniq ~eq s remove consecutive duplicate characters in s.

  • since 3.4
val flat_map : ?sep:string -> f:(char -> string) -> string -> string

flat_map ?sep ~f s maps each chars of s to a string, then concatenates them all.

  • parameter sep

    optional separator between each generated string.

  • since 0.12
val for_all : f:(char -> bool) -> string -> bool

for_all ~f s is true iff all characters of s satisfy the predicate f.

  • since 0.12
val exists : f:(char -> bool) -> string -> bool

exists ~f s is true iff some character of s satisfy the predicate f.

  • since 0.12
val drop_while : f:(char -> bool) -> t -> t

drop_while ~f s discards any characters of s starting from the left, up to the first character c not satisfying f c.

  • since 2.2
val rdrop_while : f:(char -> bool) -> t -> t

rdrop_while ~f s discards any characters of s starting from the right, up to the first character c not satisfying f c.

  • since 2.2
val ltrim : t -> t

ltrim s trims space on the left (see String.trim for more details).

  • since 1.2
val rtrim : t -> t

rtrim s trims space on the right (see String.trim for more details).

  • since 1.2

Operations on 2 strings

val map2 : f:(char -> char -> char) -> string -> string -> string

map2 ~f s1 s2 maps pairs of chars.

  • raises Invalid_argument

    if the strings have not the same length.

  • since 0.12
val iter2 : f:(char -> char -> unit) -> string -> string -> unit

iter2 ~f s1 s2 iterates on pairs of chars.

  • raises Invalid_argument

    if the strings have not the same length.

  • since 0.12
val iteri2 : f:(int -> char -> char -> unit) -> string -> string -> unit

iteri2 ~f s1 s2 iterates on pairs of chars with their index.

  • raises Invalid_argument

    if the strings have not the same length.

  • since 0.12
val fold2 : f:('a -> char -> char -> 'a) -> init:'a -> string -> string -> 'a

fold2 ~f ~init s1 s2 folds on pairs of chars.

  • raises Invalid_argument

    if the strings have not the same length.

  • since 0.12
val for_all2 : f:(char -> char -> bool) -> string -> string -> bool

for_all2 ~f s1 s2 returns true iff all pairs of chars satisfy the predicate f.

  • raises Invalid_argument

    if the strings have not the same length.

  • since 0.12
val exists2 : f:(char -> char -> bool) -> string -> string -> bool

exists2 ~f s1 s2 returns true iff a pair of chars satisfy the predicate f.

  • raises Invalid_argument

    if the strings have not the same length.

  • since 0.12

Ascii functions

Those functions are deprecated in String since 4.03, so we provide a stable alias for them even in older versions.

val capitalize_ascii : string -> string

capitalize_ascii s returns a copy of s with the first character set to uppercase using the US-ASCII character set. See String.

  • since 0.18
val uncapitalize_ascii : string -> string

uncapitalize_ascii s returns a copy of s with the first character set to lowercase using the US-ASCII character set. See String.

  • since 0.18
val uppercase_ascii : string -> string

uppercase_ascii s returns a copy of s with all lowercase letters translated to uppercase using the US-ASCII character set. See String.

  • since 0.18
val lowercase_ascii : string -> string

lowercase_ascii s returns a copy of s with all uppercase letters translated to lowercase using the US-ASCII character set. See String.

  • since 0.18
val equal_caseless : string -> string -> bool

equal_caseless s1 s2 compares s1 and s2 without respect to ascii lowercase.

  • since 1.2
val to_hex : string -> string

Convert a string with arbitrary content into a hexadecimal string.

  • since 3.8
val of_hex : string -> string option

Convert a string in hex into a string with arbitrary content.

  • since 3.8
val of_hex_exn : string -> string

Same as of_hex but fails harder.

  • raises Invalid_argument

    if the input is not valid hex.

  • since 3.8

Finding

A relatively efficient algorithm for finding sub-strings.

  • since 1.0
module Find : sig ... end

Splitting

module Split : sig ... end
val split_on_char : by:char -> string -> string list

split_on_char ~by s splits the string s along the given char by.

  • since 1.2
val split : by:string -> string -> string list

split ~by s splits the string s along the given string by. Alias to Split.list_cpy.

  • since 1.2

Utils

val compare_versions : string -> string -> int

compare_versions s1 s2 compares version strings s1 and s2, considering that numbers are above text.

  • since 0.13
val compare_natural : string -> string -> int

compare_natural s1 s2 is the Natural Sort Order, comparing chunks of digits as natural numbers. https://en.wikipedia.org/wiki/Natural_sort_order

  • since 1.3
val edit_distance : ?cutoff:int -> string -> string -> int

edit_distance ?cutoff s1 s2 is the edition distance between the two strings s1 and s2. This satisfies the classical distance axioms: it is always positive, symmetric, and satisfies the formula distance s1 s2 + distance s2 s3 >= distance s1 s3.

  • parameter cutoff

    if provided, it's a cap on both the number of iterations, and on the result. (since 3.0). This is useful if you just want to check whether the edit distance is less or equal than 2 (use cutoff of 3).

Infix operators

  • since 3.0
module Infix : sig ... end
include module type of Infix
val (=) : t -> t -> bool
  • since 3.0
val (<>) : t -> t -> bool
  • since 3.0
val (<) : t -> t -> bool
  • since 3.0
val (<=) : t -> t -> bool
  • since 3.0
val (>=) : t -> t -> bool
  • since 3.0
val (>) : t -> t -> bool
  • since 3.0