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Standard Library

Below is the API for the OCaml standard library. It's directly copied over from the OCaml Manual, formatted to the Reason syntax and styled accordingly. The API docs are work-in-progress; we'll be polishing these gradually!

If you're targeting JavaScript, the API docs for BuckleScript includes all of below, plus JS-specific APIs.

Module Str

module Str: sig .. end
Regular expressions and high-level string processing


Regular expressions

type regexp;
The type of compiled regular expressions.
let regexp: string => regexp;
Compile a regular expression. The following constructs are recognized:
  • . Matches any character except newline.
  • * (postfix) Matches the preceding expression zero, one or several times
  • + (postfix) Matches the preceding expression one or several times
  • ? (postfix) Matches the preceding expression once or not at all
  • [..] Character set. Ranges are denoted with -, as in [a-z]. An initial ^, as in [^0-9], complements the set. To include a ] character in a set, make it the first character of the set. To include a - character in a set, make it the first or the last character of the set.
  • ^ Matches at beginning of line (either at the beginning of the matched string, or just after a newline character).
  • $ Matches at end of line (either at the end of the matched string, or just before a newline character).
  • \| (infix) Alternative between two expressions.
  • \(..\) Grouping and naming of the enclosed expression.
  • \1 The text matched by the first \(...\) expression (\2 for the second expression, and so on up to \9).
  • \b Matches word boundaries.
  • \ Quotes special characters. The special characters are $^\.*+?[].
Note: the argument to regexp is usually a string literal. In this case, any backslash character in the regular expression must be doubled to make it past the OCaml string parser. For example, the following expression:
 let r = Str.regexp "hello \\([A-Za-z]+\\)" in
      Str.replace_first r "\\1" "hello world" 
returns the string "world".

In particular, if you want a regular expression that matches a single backslash character, you need to quote it in the argument to regexp (according to the last item of the list above) by adding a second backslash. Then you need to quote both backslashes (according to the syntax of string constants in OCaml) by doubling them again, so you need to write four backslash characters: Str.regexp "\\\\".

let regexp_case_fold: string => regexp;
Same as regexp, but the compiled expression will match text in a case-insensitive way: uppercase and lowercase letters will be considered equivalent.
let quote: string => string;
Str.quote s returns a regexp string that matches exactly s and nothing else.
let regexp_string: string => regexp;
Str.regexp_string s returns a regular expression that matches exactly s and nothing else.
let regexp_string_case_fold: string => regexp;
Str.regexp_string_case_fold is similar to Str.regexp_string, but the regexp matches in a case-insensitive way.

String matching and searching

let string_match: (regexp, string, int) => bool;
string_match r s start tests whether a substring of s that starts at position start matches the regular expression r. The first character of a string has position 0, as usual.
let search_forward: (regexp, string, int) => int;
search_forward r s start searches the string s for a substring matching the regular expression r. The search starts at position start and proceeds towards the end of the string. Return the position of the first character of the matched substring.
Raises Not_found if no substring matches.
let search_backward: (regexp, string, int) => int;
search_backward r s last searches the string s for a substring matching the regular expression r. The search first considers substrings that start at position last and proceeds towards the beginning of string. Return the position of the first character of the matched substring.
Raises Not_found if no substring matches.
let string_partial_match: (regexp, string, int) => bool;
Similar to Str.string_match, but also returns true if the argument string is a prefix of a string that matches. This includes the case of a true complete match.
let matched_string: string => string;
matched_string s returns the substring of s that was matched by the last call to one of the following matching or searching functions: provided that none of the following functions was called inbetween: Note: in the case of global_substitute and substitute_first, a call to matched_string is only valid within the subst argument, not after global_substitute or substitute_first returns.

The user must make sure that the parameter s is the same string that was passed to the matching or searching function.

let match_beginning: unit => int;
match_beginning() returns the position of the first character of the substring that was matched by the last call to a matching or searching function (see Str.matched_string for details).
let match_end: unit => int;
match_end() returns the position of the character following the last character of the substring that was matched by the last call to a matching or searching function (see Str.matched_string for details).
let matched_group: (int, string) => string;
matched_group n s returns the substring of s that was matched by the nth group \(...\) of the regular expression that was matched by the last call to a matching or searching function (see Str.matched_string for details). The user must make sure that the parameter s is the same string that was passed to the matching or searching function.
Raises Not_found if the nth group of the regular expression was not matched. This can happen with groups inside alternatives \|, options ? or repetitions *. For instance, the empty string will match \(a\)*, but matched_group 1 "" will raise Not_found because the first group itself was not matched.
let group_beginning: int => int;
group_beginning n returns the position of the first character of the substring that was matched by the nth group of the regular expression that was matched by the last call to a matching or searching function (see Str.matched_string for details).
Raises
  • Not_found if the nth group of the regular expression was not matched.
  • Invalid_argument if there are fewer than n groups in the regular expression.
let group_end: int => int;
group_end n returns the position of the character following the last character of substring that was matched by the nth group of the regular expression that was matched by the last call to a matching or searching function (see Str.matched_string for details).
Raises
  • Not_found if the nth group of the regular expression was not matched.
  • Invalid_argument if there are fewer than n groups in the regular expression.

Replacement

let global_replace: (regexp, string, string) => string;
global_replace regexp templ s returns a string identical to s, except that all substrings of s that match regexp have been replaced by templ. The replacement template templ can contain \1, \2, etc; these sequences will be replaced by the text matched by the corresponding group in the regular expression. \0 stands for the text matched by the whole regular expression.
let replace_first: (regexp, string, string) => string;
Same as Str.global_replace, except that only the first substring matching the regular expression is replaced.
let global_substitute: (regexp, string => string, string) => string;
global_substitute regexp subst s returns a string identical to s, except that all substrings of s that match regexp have been replaced by the result of function subst. The function subst is called once for each matching substring, and receives s (the whole text) as argument.
let substitute_first: (regexp, string => string, string) => string;
Same as Str.global_substitute, except that only the first substring matching the regular expression is replaced.
let replace_matched: (string, string) => string;
replace_matched repl s returns the replacement text repl in which \1, \2, etc. have been replaced by the text matched by the corresponding groups in the regular expression that was matched by the last call to a matching or searching function (see Str.matched_string for details). s must be the same string that was passed to the matching or searching function.

Splitting

let split: (regexp, string) => list(string);
split r s splits s into substrings, taking as delimiters the substrings that match r, and returns the list of substrings. For instance, split (regexp "[ \t]+") s splits s into blank-separated words. An occurrence of the delimiter at the beginning or at the end of the string is ignored.
let bounded_split: (regexp, string, int) => list(string);
Same as Str.split, but splits into at most n substrings, where n is the extra integer parameter.
let split_delim: (regexp, string) => list(string);
Same as Str.split but occurrences of the delimiter at the beginning and at the end of the string are recognized and returned as empty strings in the result. For instance, split_delim (regexp " ") " abc " returns [""; "abc"; ""], while split with the same arguments returns ["abc"].
let bounded_split_delim: (regexp, string, int) => list(string);
Same as Str.bounded_split, but occurrences of the delimiter at the beginning and at the end of the string are recognized and returned as empty strings in the result.
type split_result = 
| Text of string
| Delim of string
let full_split: (regexp, string) => list(split_result);
Same as Str.split_delim, but returns the delimiters as well as the substrings contained between delimiters. The former are tagged Delim in the result list; the latter are tagged Text. For instance, full_split (regexp "[{}]") "{ab}" returns [Delim "{"; Text "ab"; Delim "}"].
let bounded_full_split: (regexp, string, int) => list(split_result);
Same as Str.bounded_split_delim, but returns the delimiters as well as the substrings contained between delimiters. The former are tagged Delim in the result list; the latter are tagged Text.

Extracting substrings

let string_before: (string, int) => string;
string_before s n returns the substring of all characters of s that precede position n (excluding the character at position n).
let string_after: (string, int) => string;
string_after s n returns the substring of all characters of s that follow position n (including the character at position n).
let first_chars: (string, int) => string;
first_chars s n returns the first n characters of s. This is the same function as Str.string_before.
let last_chars: (string, int) => string;
last_chars s n returns the last n characters of s.