Stdlib.StringLabels(3)

📦
version 5.5.0 · 19 versions
, in arch rolling

💖 Stdlib.StringLabels 💖

okay bestie, welcome to the Stdlib.StringLabels page from the OCaml library — the manual literally has Stdlib.StringLabels(3) sitting up top, but we’re folding that name in right here so you’re oriented 💅. This page is long, so it’s part 1 of 3 (more incoming, don’t panic).

✨ NAME ✨

Stdlib.StringLabels - no description

🧩 Module 🧩

Module Stdlib.StringLabels

📖 Documentation 📖

Module StringLabels : (module Stdlib__StringLabels)

🧵 Strings 🧵

  • type t = string — the type for strings. periodt 💖
  • val make : int -> char -> string — make n c is a string of length n with each index holding the character c.
⚠️ Raises Invalid_argument if n < 0 or n > Sys.max_string_length.
  • 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 ✨

⚠️ Raises Invalid_argument if n < 0 or n > Sys.max_string_length.
  • val empty : string — the empty string.

Since 4.13 🎀

  • val length : string -> int — length s is the length (number of bytes/characters) of s.
  • 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.
  • val of_char : char -> string — of_char c is c as a string.

Since 5.5 🦋

  • val of_bytes : bytes -> string — return a new string that contains the same bytes as the given byte sequence.

Since 4.13 🌸

  • val to_bytes : string -> bytes — return a new byte sequence that contains the same bytes as the given string.

Since 4.13 🌈

  • val blit : src:string -> src_pos:int -> dst:bytes -> dst_pos:int -> len:int -> unit — same as Bytes.blit_string which should be preferred.

🔗 Concatenating 🔗

note: The (^) 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.
⚠️ Raises Invalid_argument if the result is longer than Sys.max_string_length bytes.
  • val cat : string -> string -> string — cat s1 s2 concatenates s1 and s2 (s1 ^ s2).

Since 4.13 ⭐

⚠️ Raises Invalid_argument if the result is longer than Sys.max_string_length bytes.

🕵️ Predicates and comparisons 🕵️

  • val equal : t -> t -> bool — equal s0 s1 is true if and only if s0 and s1 are character-wise equal.

Since 4.05 💜

  • val compare : t -> t -> int — compare s0 s1 sorts s0 and s1 in lexicographical order. compare behaves like compare on strings but may be more efficient.
  • val is_empty : string -> bool — is_empty s is true if and only if s is an empty string.

Since 5.5 🧚

  • val starts_with : prefix:string -> string -> bool — starts_with ~prefix s is true if and only if s starts with prefix.

Since 4.13 🎀

  • val ends_with : suffix:string -> string -> bool — ends_with ~suffix s is true if and only if s ends with suffix.

Since 4.13 🎀

  • val includes : affix:string -> string -> bool — includes ~affix s is true if and only if affix occurs in s.
note: To test the same affix string multiple times, partially applying the ~affix argument and using the resulting function repeatedly is more efficient.

Since 5.5 🌟

  • 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.

🍰 Splitting strings 🍰

🧁 Splitting with magnitudes 🧁

  • val take_first : int -> string -> string — take_first n s are the first n bytes of s. This is s if n >= length s and "" if n <= 0.

Since 5.5 🍓

  • val take_last : int -> string -> string — take_last n s are the last n bytes of s. This is s if n >= length s and "" if n <= 0.

Since 5.5 🍓

  • val drop_first : int -> string -> string — drop_first n s is s without the first n bytes of s. This is "" if n >= length s and s if n <= 0.

Since 5.5 🍓

  • val drop_last : int -> string -> string — drop_last n s is s without the last n bytes of s. This is "" if n >= length s and s if n <= 0.

Since 5.5 🍓

  • val cut_first : int -> string -> string * string — cut_first n v is (take_first n v, drop_first n v).

Since 5.5 🍓

  • val cut_last : int -> string -> string * string — cut_last n v is (drop_last n v, take_last n v).

Since 5.5 🍓

🧁 Splitting with predicates 🧁

  • val take_first_while : (char -> bool) -> string -> string — take_first_while p s is the first consecutive bytes of s satisfying the predicate p.

Since 5.5 🦋

  • val take_last_while : (char -> bool) -> string -> string — take_last_while p s is the last consecutive bytes of s satisfying the predicate p.

Since 5.5 🦋

  • val drop_first_while : (char -> bool) -> string -> string — drop_first_while p s is s without the first consecutive bytes of s satisfying the predicate p.

Since 5.5 🦋

  • val drop_last_while : (char -> bool) -> string -> string — drop_last_while p s is s without the last consecutive bytes of s satisfying the predicate p.

Since 5.5 🦋

  • val cut_first_while : (char -> bool) -> string -> string * string — cut_first_while p s is (take_first_while p s, drop_first_while p s).

Since 5.5 🦋

  • val cut_last_while : (char -> bool) -> string -> string * string — cut_last_while p s is (drop_last_while p s, take_last_while p s).

Since 5.5 🦋

🧁 Splitting with separators 🧁

note: To split the same sep string multiple times, partially applying the ~sep argument of these functions and using the resulting function repeatedly is more efficient.
  • val split_first : sep:string -> string -> (string * string) option — split_first ~sep s is the pair Some (left, right) made of the two (possibly empty) substrings of s that are delimited by the first match of the separator sep in s or None if sep can't be found. Search for sep starts at position 0 and uses StringLabels.find_first.

If sep is "", this is Some ("", s).

The invariant concat sep [left; right] = s holds.

Since 5.5 💫

  • val split_last : sep:string -> string -> (string * string) option — split_last ~sep s is the pair Some (left, right) made of the two (possibly empty) substrings of s that are delimited by the last match of the separator sep in s or None if sep can't be found. Search for sep starts at position length s and uses StringLabels.find_last.

If sep is "", this is Some (s, "").

The invariant concat sep [left; right] = s holds.

Since 5.5 💫

  • val split_all : sep:string -> ?drop:(string -> bool) -> string -> string list — split_all ~sep s is the list of all substrings of s that are delimited by non-overlapping matches of the separator sep or the list [s] if sep can't be found. Search for sep starts at position 0 in increasing indexing order and uses StringLabels.find_all.

Substrings sub for which drop sub is true are not included in the result. drop defaults to Fun.const false.

If sep is "", this is [""; c0; ...; cn; ""] with ci the string of_char s.[i].

The invariant concat sep (split_all ~sep s) = s holds.

Since 5.5 💫

  • val rsplit_all : sep:string -> ?drop:(string -> bool) -> string -> string list — rsplit_all ~sep s is the list of all substrings of s that are delimited by non-overlapping matches of the separator sep or [s] if sep can't be found. Search for sep starts at position length s in decreasing indexing order and uses StringLabels.rfind_all.

Substrings sub for which drop sub is true are not included in the result. drop defaults to Fun.const false.

If sep is "", this is [""; c0; ...; cn; ""] with ci the string of_char s.[i].

The invariant concat sep (rsplit_all ~sep s) = s holds.

Since 5.5 💫

  • val split_on_char : sep:char -> string -> string list — split_on_char ~sep s is the list of all (possibly empty) substrings of s that are delimited by the character sep. If s is empty, the result is the singleton list [""].

The function's result 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 ( concat (make 1 sep)
      (split_on_char sep s) = s ).

-No string in the result contains the sep character.

Since 4.05 💜

🔄 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 ✨

  • val mapi : f:(int -> char -> char) -> string -> string — mapi ~f s is like StringLabels.map but the index of the character is also passed to f.

Since 4.02 ✨

  • val fold_left : f:('acc -> char -> 'acc) -> init:'acc -> string -> 'acc — 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 🌈

  • val fold_right : f:(char -> 'acc -> 'acc) -> string -> init:'acc -> 'acc — 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 🌈

  • val for_all : f:(char -> bool) -> string -> bool — for_all p s checks if all characters in s satisfy the predicate p.

Since 4.13 🎀

  • val exists : f:(char -> bool) -> string -> bool — exists p s checks if at least one character of s satisfies the predicate p.

Since 4.13 🎀

  • 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 ✨

  • 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 (0x5C) 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).

⚠️ Raises Invalid_argument if the result is longer than Sys.max_string_length bytes.
  • val uppercase_ascii : string -> string — uppercase_ascii s is s with all lowercase letters translated to uppercase, using the US-ASCII character set.

Since 4.05 💜

  • val lowercase_ascii : string -> string — lowercase_ascii s is s with all uppercase letters translated to lowercase, using the US-ASCII character set.

Since 4.05 💜

  • val capitalize_ascii : string -> string

capitalize_ascii s is s but with its very first character bumped up to uppercase, US-ASCII rules only 💅 nothing fancy, no Unicode drama.

Since 4.05

  • val uncapitalize_ascii : string -> string — uncapitalize_ascii s is s with the first character knocked down to lowercase, again strictly US-ASCII. 🎀

Since 4.05

🦋 Traversing 🦋

  • val iter : f:(char -> unit) -> string -> unit — iter ~f s runs your function f over every single character of s, one after another, no skips. It's literally the same vibe as f s.[0]; f s.[1]; ...; f s.[length s - 1]; () ✨
  • val iteri : f:(int -> char -> unit) -> string -> unit — iteri is exactly like StringLabels.iter, except your function also gets handed the matching character index, so you always know where you are 🗺️

Since 4.00

🔍 Finding indices 🔍

  • val find_first_index : (char -> bool) -> ?start:int -> string -> int option — find_first_index p ~start s gives you the index of the first character of s that passes your predicate p, at or after the index (or position) start, which defaults to 0. 👑

If start is length s, the answer is always None. No cap.

Since 5.5

Raises Invalid_argument if start isn't a valid position of s.

  • val find_last_index : (char -> bool) -> ?start:int -> string -> int option — find_last_index p ~start s gives you the index of the last character of s that satisfies p, at or before the index (or position) start, which defaults to length s. 🌸

Since 5.5

Raises Invalid_argument if start isn't a valid position of s.

  • val index_from : string -> int -> char -> int — index_from s i c is the index of the first c inside s after position i. 🎯

Raises Not_found if c just… isn't in s after position i 😭

Raises Invalid_argument if i isn't 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 c in s after position i (if there even is one 🙈). Same thing as above but it won't throw hands at you.

Since 4.05

Raises Invalid_argument if i isn't a valid position in s.

  • val rindex_from : string -> int -> char -> int — rindex_from s i c is the index of the last c in s before position i+1. Going backwards, queen behavior 💅

Raises Not_found if c doesn't occur in s before position i+1.

Raises Invalid_argument if i+1 isn't 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 c in s before position i+1 (if any 🫶).

Since 4.05

Raises Invalid_argument if i+1 isn't a valid position in s.

  • val index : string -> char -> int — index s c is literally just String.index_from s 0 c. Shortcut city ⭐
  • val index_opt : string -> char -> int option — index_opt s c is String.index_from_opt s 0 c. The chill version 🦋

Since 4.05

  • val rindex : string -> char -> int — rindex s c is String.rindex_from s (length s - 1) c. Backwards search from the very end, iconic.
  • val rindex_opt : string -> char -> int option — rindex_opt s c is String.rindex_from_opt s (length s - 1) c. Same but with the option safety net 🌈

Since 4.05

🧚 Finding substrings 🧚

Note. If you're hunting for the same substring multiple times, partially applying the ~sub argument of these functions and then reusing the resulting function is more efficient. Do less work, slay more 💖
  • val find_first : sub:string -> ?start:int -> string -> int option — find_first ~sub ~start s is the starting position of the first occurrence of sub in s, at or after the index (or position) start, which defaults to 0. 🔥

If sub is "", the result is Some start. And heads up: the result of the function is always a valid index of s, except when sub is "" and start is length s. That one little edge case, iykyk 💀

Since 5.5

Raises Invalid_argument if start isn't a valid position of s.

  • val find_last : sub:string -> ?start:int -> string -> int option — find_last ~sub ~start s is the starting position of the last occurrence of sub in s, at or before the index (or position) start, which defaults to String.length s. 🌸

If sub is "", the result is Some start. Same fine print as above: the result is always a valid index of s except when sub is "" and start is length s.

Since 5.5

Raises Invalid_argument if start isn't a valid position of s.

  • val find_all : sub:string -> f:(int -> 'acc -> 'acc) -> ?start:int -> string -> 'acc -> 'acc — find_all ~sub f ~start s acc starts from acc and folds f in increasing index order over all the non-overlapping starting positions of sub in s, at or after the index (or position) start, which defaults to 0. If sub never shows up in s, you just get acc back, no harm no foul 🫶

If sub is "", then f gets invoked on all positions of s at or after start.

Since 5.5

Raises Invalid_argument if start isn't a valid position of s.

  • val rfind_all : sub:string -> f:(int -> 'acc -> 'acc) -> ?start:int -> string -> 'acc -> 'acc — rfind_all ~sub f ~start s acc starts from acc and folds f in decreasing index order over all the non-overlapping starting positions of sub in s, at or before the index (or position) start, which defaults to String.length s. Still acc if nothing's found 💜

If sub is "", then f gets invoked on all positions of s at or before start.

Since 5.5

Raises Invalid_argument if start isn't a valid position of s.

🎀 Replacing substrings 🎀

Note. Same efficiency tip as before: replacing the same substring over and over? Partially apply the ~sub argument of these functions and reuse the resulting function repeatedly. Obsessed with the efficiency ✨
  • val replace_first : sub:string -> by:string -> ?start:int -> string -> string — replace_first ~sub ~by ~start s swaps by in for the first occurrence of sub in s, at or after the index (or position) start, which defaults to 0. 🪄

If sub is "", this inserts by at position start.

Since 5.5

Raises Invalid_argument if start isn't a valid position of s.

  • val replace_last : sub:string -> by:string -> ?start:int -> string -> string — replace_last ~sub ~by ~start s replaces by by the last occurrence of sub in s, at or after the index (or position) start, which defaults to String.length s. (Yes, that's exactly how the original says it — by goes in where sub was, don't overthink it 🙈)

If sub is "", this inserts by at position start.

Since 5.5

Raises Invalid_argument if start isn't a valid position of s.

  • val replace_all : sub:string -> by:string -> ?start:int -> string -> string — replace_all ~sub ~by ~start s replaces every non-overlapping occurrence of sub in s with by, at or after the index (or position) start, which defaults to 0. Occurrences get found in increasing indexing order, left to right, methodical queen 👑

If sub is "", this inserts by at all positions from start on.

Since 5.5

Raises Invalid_argument if start isn't a valid position of s.

🌈 Strings and Sequences 🌈

  • val to_seq : t -> char Seq.t — to_seq s is a sequence built from the string's characters, in increasing order. Easy. Gorgeous. 🦋

Since 4.07

  • val to_seqi : t -> (int * char) Seq.t — to_seqi s is like StringLabels.to_seq, but it also tuples up the matching index with each character. Best of both worlds 💅

Since 4.07

  • val of_seq : char Seq.t -> t — of_seq s is a string made out of the sequence's characters. Sequence in, string out. Iconic. ⭐

Since 4.07

🧵 UTF decoding and validations 🧵

💖 UTF-8 💖

  • val get_utf_8_uchar : t -> int -> Uchar.utf_decode — get_utf_8_uchar b i decodes a UTF-8 character sitting at index i in b. 🎀
  • val is_valid_utf_8 : t -> bool — is_valid_utf_8 b is true if and only if b holds valid UTF-8 data. No cap, it really checks ✅

💜 UTF-16BE 💜

  • val get_utf_16be_uchar : t -> int -> Uchar.utf_decode — get_utf_16be_uchar b i decodes a 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 a 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. 💖

✨ Spellchecking ✨

  • val edit_distance : ?limit:int -> t -> t -> int — edit_distance s0 s1 is the number of single-character edits (insertion, deletion, substitution, transposition — the whole glow-up menu) needed to turn s0 into s1. 💅

If you pass limit, the function bails and returns limit the moment it's determined that s0 and s1 are at least limit apart. That's faster when you've got a fixed limit — like, say, for spellchecking 👀

Heads up on the encoding: the function assumes the strings are UTF-8 encoded and uses Uchar.t for its notion of "character". Decoding errors get replaced by Uchar.rep. And normalizing your strings to NFC gives better results, so do that 🎀

Note. This implements the simpler Optimal String Alignment (OSA) distance, not the Damerau-Levenshtein distance. Which means with this function "ca" and "abc" have a distance of 3, not 2. Fr fr, don't @ me 💀

Since 5.4

  • val spellcheck : ?max_dist:(string -> int) -> ((string -> unit) -> unit) -> string -> string list — spellcheck iter_dict s gives you the strings enumerated by the iterator iter_dict whose StringLabels.edit_distance to s is the smallest and at most max_dist s. If multiple corrections come back, their order is as found in iter_dict — respect the source order 🫶

The default max_dist s is:

  • 0 if s has 0 to 2 Unicode characters.
  • 1 if s has 3 to 4 Unicode characters.
  • 2 otherwise.

If your dictionary happens to be a list l, a suitable iter_dict is given by (fun yield -> List.iter yield l). Chef's kiss 🤌

All strings are assumed to be UTF-8 encoded, and decoding errors are replaced by Uchar.rep characters.

Since 5.4

🔥 Binary decoding of integers 🔥

The functions in this section binary decode integers from strings. Yes, we're going full low-level, and honestly? It slaps.

All the following functions raise Invalid_argument if the characters needed at index i to decode the integer aren't available. 😭

Little-endian (resp. big-endian) encoding means that the least (resp. most) significant bytes are stored first. Big-endian is also known as network byte order — that's the one your networking friends keep bringing up. 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. Those extra bits are sign-extended (or zero-extended) for functions that decode 8-bit or 16-bit integers and represent them with int values. Tiny numbers, big shoes 💖

  • 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

  • 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

  • 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

  • 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

  • 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

  • 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

  • val get_int16_be : string -> int -> int

Okay so these next ones are the byte-decoding girlies — they read raw integers straight out of a string at a character index. Same shape every time: you hand them the string b and an index i, they hand you back a number. Obsessed. 💅

  • 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

  • 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

  • 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. Bestie, native-endian is literally "whatever your machine feels like," iykyk. 💀

Since 4.13

Okay plot twist — the doc just casually drops the hash functions here in the middle of the endian-ness parade. Not me getting whiplash 😭 but slay, we keep the original order, always. ✨

  • val hash : t -> int — an unseeded hash function for strings, with the same output value as Hashtbl.hash. The whole point? It lets this module be passed as an argument to the functor Hashtbl.Make. 👑

Since 5.0

  • val seeded_hash : int -> t -> int — a seeded hash function for strings, with the same output value as Hashtbl.seeded_hash. And this one lets this module be passed as an argument to the functor Hashtbl.MakeSeeded. 🫶

Since 5.0

And we're back to the endian content, no notes. 🦋

  • 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

  • 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

  • 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. Big number energy 🔥

Since 4.13

  • 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

  • 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

And that's the whole page bestie!! 🎉💖 You made it to the end of part three, which honestly deserves a little reward. Go drink some water. 🌸

That's a wrap from OCamldoc, dated 2026-06-22, covering Stdlib.StringLabels(3) — mwah, take care of her 🫶✨

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