Module Astring.String

Strings, substrings, string sets and maps.

A string s of length l is a zero-based indexed sequence of l bytes. An index i of s is an integer in the range [0;l-1], it represents the ith byte of s which can be accessed using the string indexing operator s.[i].

Important. OCaml's strings became immutable since 4.02. Whenever possible compile your code with the -safe-string option. This module does not expose any mutable operation on strings and assumes strings are immutable. See the porting guide.

String

type t = string

The type for strings. Finite sequences of immutable bytes.

val empty : string

empty is an empty string.

val v : len:int -> (int -> char) -> string

v len f is a string s of length len with s.[i] = f i for all indices i of s. f is invoked in increasing index order.

raises Invalid_argument

if len is not in the range [0; Sys.max_string_length].

val length : string -> int

length s is the number of bytes in s.

val get : string -> int -> char

get s i is the byte of s' at index i. This is equivalent to the s.[i] notation.

raises Invalid_argument

if i is not an index of s.

val get_byte : string -> int -> int

get_byte s i is Char.to_int (get s i)

val head : ?⁠rev:bool -> string -> char option

head s is Some (get s h) with h = 0 if rev = false (default) or h = length s - 1 if rev = true. None is returned if s is empty.

val get_head : ?⁠rev:bool -> string -> char

get_head s is like head but

raises Invalid_argument

if s is empty.

val hash : string -> int

hash s is Hashtbl.hash s.

Appending strings

val append : string -> string -> string

append s s' appends s' to s. This is equivalent to s ^ s'.

raises Invalid_argument

if the result is longer than Sys.max_string_length.

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

concat ~sep ss concatenates the list of strings ss, separating each consecutive elements in the list ss with sep (defaults to empty).

raises Invalid_argument

if the result is longer than Sys.max_string_length.

Predicates

val is_empty : string -> bool

is_empty s is length s = 0.

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 in s such that for all indices i of affix we have affix.[i] = s.[j + i].

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

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

val equal : string -> string -> bool

equal s s' is s = s'.

val compare : string -> string -> int

compare s s' is Stdlib.compare s s', it compares the byte sequences of s and s' in lexicographical order.

Extracting substrings

Tip. These functions extract substrings as new strings. Using substrings may be less wasteful and more flexible.

val with_range : ?⁠first:int -> ?⁠len:int -> string -> string

with_range ~first ~len s are the consecutive bytes of s whose indices exist in the range [first;first + len - 1].

first defaults to 0 and len to max_int. Note that first can be any integer and len any positive integer.

raises Invalid_argument

if len is negative.

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.

val trim : ?⁠drop:(char -> bool) -> string -> string

trim ~drop s is s with prefix and suffix bytes satisfying drop in s removed. drop defaults to Char.Ascii.is_white.

val span : ?⁠rev:bool -> ?⁠min:int -> ?⁠max:int -> ?⁠sat:(char -> bool) -> string -> string * string

span ~rev ~min ~max ~sat s is (l, r) where:

  • if rev is false (default), l is at least min and at most max consecutive sat satisfying initial bytes of s or empty if there are no such bytes. r are the remaining bytes of s.
  • if rev is true, r is at least min and at most max consecutive sat satisfying final bytes of s or empty if there are no such bytes. l are the remaining the bytes of s.

If max is unspecified the span is unlimited. If min is unspecified it defaults to 0. If min > max the condition can't be satisfied and the left or right span, depending on rev, is always empty. sat defaults to (fun _ -> true).

The invariant l ^ r = s holds.

raises Invalid_argument

if max or min is negative.

val take : ?⁠rev:bool -> ?⁠min:int -> ?⁠max:int -> ?⁠sat:(char -> bool) -> string -> string

take ~rev ~min ~max ~sat s is the matching span of span without the remaining one. In other words:

(if rev then snd else fst) @@ span ~rev ~min ~max ~sat s
val drop : ?⁠rev:bool -> ?⁠min:int -> ?⁠max:int -> ?⁠sat:(char -> bool) -> string -> string

drop ~rev ~min ~max ~sat s is the remaining span of span without the matching span. In other words:

(if rev then fst else snd) @@ span ~rev ~min ~max ~sat s
val cut : ?⁠rev:bool -> 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 non empty separator string sep or None if sep can't be matched in s. Matching starts from the beginning of s (rev is false, default) or the end (rev is true).

The invariant l ^ sep ^ r = s holds.

raises Invalid_argument

if sep is the empty string.

val cuts : ?⁠rev:bool -> ?⁠empty:bool -> sep:string -> string -> string list

cuts 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 empty is false (defaults to true).

Matching separators in s starts from the beginning 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 ~empty:true ~sep s) = s
  • cuts ~empty:true ~sep s <> []
raises Invalid_argument

if sep is the empty string.

val fields : ?⁠empty:bool -> ?⁠is_sep:(char -> bool) -> string -> string list

fields ~empty ~is_sep s is the list of (possibly empty) substrings that are delimited by bytes for which is_sep is true. Empty substrings are omitted in the list if empty is false (defaults to true). is_sep defaults to Char.Ascii.is_white.

Substrings

type sub

The type for substrings.

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

sub is Sub.v.

val sub_with_range : ?⁠first:int -> ?⁠len:int -> string -> sub

sub_with_range is like with_range but returns a substring value. If first is smaller than 0 the empty string at the start of s is returned. If first is greater than the last index of s the empty string at the end of s is returned.

val sub_with_index_range : ?⁠first:int -> ?⁠last:int -> string -> sub

sub_with_index_range is like with_index_range but returns a substring value. If first and last are smaller than 0 the empty string at the start of s is returned. If first and is greater than the last index of s the empty string at the end of s is returned. If first > last and first is an index of s the empty string at first is returned.

module Sub : sig ... end

Substrings.

Traversing strings

val find : ?⁠rev:bool -> ?⁠start:int -> (char -> bool) -> string -> int option

find ~rev ~start sat s is:

  • If rev is false (default). The smallest index i, if any, greater or equal to start such that sat s.[i] is true. start defaults to 0.
  • If rev is true. The greatest index i, if any, smaller or equal to start such that sat s.[i] is true. start defaults to String.length s - 1.

Note that start can be any integer.

val find_sub : ?⁠rev:bool -> ?⁠start:int -> sub:string -> string -> int option

find_sub ~rev ~start ~sub s is:

  • If rev is false (default). The smallest index i, if any, greater or equal to start such that sub can be found starting at i in s that is s.[i] = sub.[0], s.[i+1] = sub.[1], ... start defaults to 0.
  • If rev is true. The greatest index i, if any, smaller or equal to start such that sub can be found starting at i in s that is s.[i] = sub.[0], s.[i+1] = sub.[1], ... start defaults to String.length s - 1.

Note that start can be any integer.

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

filter sat s is the string made of the bytes of s that satisfy sat, in the same order.

val filter_map : (char -> char option) -> string -> string

filter_map f s is the string made of the bytes of s as mapped by f, in the same order.

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.

val fold_left : ('a -> char -> 'a) -> 'a -> string -> 'a

fold_left f acc s is f (...(f (f acc s.[0]) s.[1])...) s.[m] with m = String.length s - 1.

val fold_right : (char -> 'a -> 'a) -> string -> 'a -> 'a

fold_right f s acc is f s.[0] (f s.[1] (...(f s.[m] acc) )...) with m = String.length s - 1.

val iter : (char -> unit) -> string -> unit

iter f s is f s.[0]; f s.[1]; ... f s.[m] with m = String.length s - 1.

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

iteri f s is f 0 s.[0]; f 1 s.[1]; ... f m s.[m] with m = String.length s - 1.

Uniqueness

val uniquify : string list -> string list

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

Strings as US-ASCII character sequences

module Ascii : sig ... end

US-ASCII string support.

Pretty printing

val pp : Stdlib.Format.formatter -> string -> unit

pp ppf s prints s's bytes on ppf.

val dump : Stdlib.Format.formatter -> string -> unit

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

String sets and maps

type set

The type for string sets.

module Set : sig ... end

String sets.

type +'a map

The type for maps from strings to values of type 'a.

module Map : sig ... end

String maps.

OCaml base type conversions

val of_char : char -> string

of_char c is a string that contains the byte c.

val to_char : string -> char option

to_char s is the single byte in s or None if there is no byte or more than one in s.

val of_bool : bool -> string

of_bool b is a string representation for b. Relies on Stdlib.string_of_bool.

val to_bool : string -> bool option

to_bool s is a bool from s, if any. Relies on Stdlib.bool_of_string.

val of_int : int -> string

of_int i is a string representation for i. Relies on Stdlib.string_of_int.

val to_int : string -> int option

to_int is an int from s, if any. Relies on Stdlib.int_of_string.

val of_nativeint : nativeint -> string

of_nativeint i is a string representation for i. Relies on Nativeint.of_string.

val to_nativeint : string -> nativeint option

to_nativeint is an nativeint from s, if any. Relies on Nativeint.to_string.

val of_int32 : int32 -> string

of_int32 i is a string representation for i. Relies on Int32.of_string.

val to_int32 : string -> int32 option

to_int32 is an int32 from s, if any. Relies on Int32.to_string.

val of_int64 : int64 -> string

of_int64 i is a string representation for i. Relies on Int64.of_string.

val to_int64 : string -> int64 option

to_int64 is an int64 from s, if any. Relies on Int64.to_string.

val of_float : float -> string

of_float f is a string representation for f. Relies on Stdlib.string_of_float.

val to_float : string -> float option

to_float s is a float from s, if any. Relies on Stdlib.float_of_string.