center s len pad centers s in a string of length len, padding with pad. If s is longer than len, it is returned unchanged. Padding is inserted symmetrically. pad must be non-empty or it is ignored.

This function is Unicode-aware and counts characters, not bytes. If pad is multibyte, it is repeated and truncated as needed.

Examples:

• center "hello" 10 " " returns " hello "
• center "abc" 7 "あ" returns "ああabcああ"

• parameter s

  The string to center (UTF-8)

• parameter len

  The total length (in Unicode characters) of the result

• parameter pad

  The padding string (UTF-8, non-empty)

• returns

  The centered string

count str pattern counts how many Unicode characters in str match pattern.

The pattern supports:

• character sets: e.g., "aeiou"
• ranges: e.g., "a-k", "あ-ん"
• negation with ^: e.g., "^a-k", "^0-9"

This function is Unicode-aware and handles UTF-8 properly.

Examples:

• count "hello" "aeiou" returns 2
• count "abc123" "^a-z" returns 3
• count "こんにちは" "あ-ん" returns 5

• parameter str

  The input string (UTF-8)

• parameter pattern

  The character pattern (see above)

• returns

  The number of matching characters

delete str pattern removes all Unicode characters in str that match pattern.

The pattern supports:

• character sets: e.g., "aeiou"
• ranges: e.g., "a-k", "あ-ん"
• negation with ^: e.g., "^a-k", "^0-9"

This function is Unicode-aware and handles UTF-8 properly.

Examples:

• delete "hello" "aeiou" returns "hll"
• delete "こんにちは" "こ" returns "んにちは"
• delete "abc123" "^a-z" returns "abc"

• parameter str

  The input string (UTF-8)

• parameter pattern

  The character pattern (see above)

• returns

  The string with matched characters removed

len str returns the number of Unicode code points (runes) in UTF-8 string str.

This function is Unicode-aware and counts characters, not bytes.

Examples:

• len "hello" returns 5
• len "こんにちは" returns 5
• len "🍎🍏🍊" returns 3

• parameter str

  The input string (UTF-8)

• returns

  The number of Unicode code points in str

reverse s reverses a UTF-8 encoded string s.

This function is Unicode-aware and reverses by code points, not bytes.

Examples:

• reverse "hello" returns "olleh"
• reverse "こんにちは" returns "はちにんこ"
• reverse "🍎🍏🍊" returns "🍊🍏🍎"

• parameter s

  The input string (UTF-8)

• returns

  The reversed string

contains s substr reports whether substr is within s.

Returns true if substr is the empty string, or if substr occurs anywhere in s. Returns false otherwise.

This function is Unicode-agnostic and operates on bytes, not code points.

Examples:

• contains "seafood" "foo" returns true
• contains "seafood" "bar" returns false
• contains "seafood" "" returns true
• contains "" "" returns true

• parameter s

  The input string

• parameter substr

  The substring to search for

• returns

  true if substr is found in s, false otherwise

contains_any s chars reports whether any Unicode code points in chars are within s.

Returns false if chars is empty. Unicode-aware and compares by code points.

Examples:

• contains_any "team" "i" returns false
• contains_any "fail" "ui" returns true
• contains_any "ure" "ui" returns true
• contains_any "failure" "ui" returns true
• contains_any "foo" "" returns false
• contains_any "" "" returns false

• parameter s

  The input string (UTF-8)

• parameter chars

  The set of Unicode code points to search for (UTF-8)

• returns

  true if any code point in chars is found in s, false otherwise

has_prefix s prefix reports whether the string s begins with prefix.

Returns true if prefix is the empty string, or if s starts with prefix. Returns false otherwise.

This function is Unicode-agnostic and operates on bytes, not code points.

Examples:

• has_prefix "Gopher" "Go" returns true
• has_prefix "Gopher" "C" returns false
• has_prefix "Gopher" "" returns true

• parameter s

  The input string

• parameter prefix

  The prefix to test

• returns

  true if s starts with prefix, false otherwise

has_suffix s suffix reports whether the string s ends with suffix.

Returns true if suffix is the empty string, or if s ends with suffix. Returns false otherwise.

This function is Unicode-agnostic and operates on bytes, not code points.

Examples:

• has_suffix "Amigo" "go" returns true
• has_suffix "Amigo" "O" returns false
• has_suffix "Amigo" "Ami" returns false
• has_suffix "Amigo" "" returns true

• parameter s

  The input string

• parameter suffix

  The suffix to test

• returns

  true if s ends with suffix, false otherwise

count_substring s substr counts the number of non-overlapping instances of substr in s.

If substr is the empty string, returns 1 + the number of Unicode code points in s.

This function is Unicode-agnostic and operates on bytes, not code points.

Examples:

• count_substring "cheese" "e" returns 3
• count_substring "five" "" returns 5
• count_substring "banana" "na" returns 2
• count_substring "aaaaa" "aa" returns 2
• count_substring "" "" returns 1
• count_substring "" "a" returns 0

• parameter s

  The input string

• parameter substr

  The substring to count

• returns

  The number of non-overlapping instances of substr in s

equal_fold s t reports whether s and t, interpreted as UTF-8 strings, are equal under simple Unicode case-folding (ASCII only).

This is a simple case-insensitive comparison for ASCII letters only. (It does not perform full Unicode case folding.)

Examples:

• equal_fold "Go" "go" returns true
• equal_fold "AB" "ab" returns true
• equal_fold "ß" "ss" returns false

• parameter s

  The first string (UTF-8)

• parameter t

  The second string (UTF-8)

• returns

  true if s and t are equal under simple case folding, false otherwise

fields s splits the string s around each instance of one or more consecutive Unicode whitespace characters, returning a list of substrings of s or an empty list if s contains only whitespace.

Whitespace is defined by Unicode (see is_space).

Examples:

• fields " foo bar baz " returns ["foo"; "bar"; "baz"]
• fields " " returns []
• fields "a\tb\nc" returns ["a"; "b"; "c"]

• parameter s

  The input string (UTF-8)

• returns

  List of non-whitespace substrings of s

fields_func s f splits the string s at each run of Unicode code points c satisfying f c, returning a list of substrings of s or an empty list if all code points in s satisfy f or s is empty.

Examples:

• fields_func " foo1;bar2,baz3..." (fun c -> not (is_letter c || is_number c)) returns ["foo1"; "bar2"; "baz3"]

• parameter s

  The input string (UTF-8)

• parameter f

  The predicate function on Unicode code points

• returns

  List of non-separator substrings of s

index s substr returns the index of the first instance of substr in s, or -1 if substr is not present.

The index is a byte offset (not code point index).

Examples:

• index "chicken" "ken" returns 4
• index "chicken" "dmr" returns -1
• index "abc" "" returns 0
• index "" "" returns 0
• index "" "a" returns -1

• parameter s

  The input string

• parameter substr

  The substring to search for

• returns

  The byte index of the first occurrence, or -1 if not found

repeat s count returns a new string consisting of count copies of s.

Raises Invalid_argument if count is negative.

Examples:

• repeat "na" 2 returns "nana"
• repeat "🍎" 3 returns "🍎🍎🍎"
• repeat "" 5 returns ""
• repeat "a" 0 returns ""
• repeat "abc" (-1) raises Invalid_argument

• parameter s

  The string to repeat

• parameter count

  The number of times to repeat s

• returns

  The repeated string

join elems sep concatenates the elements of elems, inserting sep between each element.

Returns the empty string if elems is empty.

Examples:

• join ["foo"; "bar"; "baz"] ", " returns "foo, bar, baz"
• join [] ", " returns ""
• join ["a"] ", " returns "a"

• parameter elems

  The list of strings to join

• parameter sep

  The separator string

• returns

  The joined string

trim s cutset returns s with all leading and trailing Unicode code points contained in cutset removed.

This function is Unicode-aware and trims by code points, not bytes.

Examples:

• trim "¡¡¡Hello, Camels!!!" "!¡" returns "Hello, Camels"

• parameter s

  The input string (UTF-8)

• parameter cutset

  The set of Unicode code points to trim (UTF-8)

• returns

  The trimmed string

trim_func s f returns s with all leading and trailing Unicode code points c satisfying f c removed.

This function is Unicode-aware and trims by code points, not bytes.

Examples:

• trim_func "¡¡¡Hello, Camels!!!" (fun c -> not (is_letter c || is_number c)) returns "Hello, Camels"

• parameter s

  The input string (UTF-8)

• parameter f

  The predicate function on Unicode code points

• returns

  The trimmed string

trim_left s cutset returns s with all leading Unicode code points contained in cutset removed.

This function is Unicode-aware and trims by code points, not bytes.

Examples:

• trim_left "¡¡¡Hello, Camels!!!" "!¡" returns "Hello, Camels!!!"

• parameter s

  The input string (UTF-8)

• parameter cutset

  The set of Unicode code points to trim (UTF-8)

• returns

  The trimmed string

trim_left_func s f returns s with all leading Unicode code points c satisfying f c removed.

This function is Unicode-aware and trims by code points, not bytes.

Examples:

• trim_left_func "¡¡¡Hello, Camels!!!" (fun c -> not (is_letter c || is_number c)) returns "Hello, Camels!!!"

• parameter s

  The input string (UTF-8)

• parameter f

  The predicate function on Unicode code points

• returns

  The trimmed string

trim_right s cutset returns s with all trailing Unicode code points contained in cutset removed.

This function is Unicode-aware and trims by code points, not bytes.

Examples:

• trim_right "¡¡¡Hello, Camels!!!" "!¡" returns "¡¡¡Hello, Camels"

• parameter s

  The input string (UTF-8)

• parameter cutset

  The set of Unicode code points to trim (UTF-8)

• returns

  The trimmed string

trim_right_func s f returns s with all trailing Unicode code points c satisfying f c removed.

This function is Unicode-aware and trims by code points, not bytes.

Examples:

• trim_right_func "¡¡¡Hello, Camels!!!" (fun c -> not (is_letter c || is_number c)) returns "¡¡¡Hello, Camels"

• parameter s

  The input string (UTF-8)

• parameter f

  The predicate function on Unicode code points

• returns

  The trimmed string

trim_space s returns s with all leading and trailing Unicode whitespace removed.

This function is Unicode-aware and trims by code points, not bytes. Whitespace is defined by Unicode (see is_space).

Examples:

• trim_space " \t\n Hello, Camels \n\t\r\n" returns "Hello, Camels"

• parameter s

  The input string (UTF-8)

• returns

  The trimmed string

trim_suffix s suffix returns s without the provided trailing suffix string. If s does not end with suffix, s is returned unchanged.

This function is byte-based, not Unicode-aware.

Examples:

• trim_suffix "¡¡¡Hello, Camels!!!" ", Camels!!!" returns "¡¡¡Hello"
• trim_suffix "¡¡¡Hello, Camels!!!" ", Marmots!!!" returns "¡¡¡Hello, Camels!!!"
• trim_suffix "abc" "" returns "abc"

• parameter s

  The input string

• parameter suffix

  The suffix to remove

• returns

  s without the trailing suffix, or s if suffix is not present

to_lower s returns s with all Unicode letters mapped to their lower case.

This function currently only lowercases ASCII letters (A-Z). Unicode-aware lowercasing is not yet implemented.

Examples:

• to_lower "Camel" returns "camel"
• to_lower "CAMEL" returns "camel"
• to_lower "こんにちは" returns "こんにちは"

• parameter s

  The input string (UTF-8)

• returns

  The lowercased string

to_title s returns s with all Unicode letters mapped to their Unicode title case.

Currently, only ASCII letters are supported (A-Z, a-z). TODO: Support full Unicode title case in the future.

Examples:

• to_title "her royal highness" returns "HER ROYAL HIGHNESS"
• to_title "loud noises" returns "LOUD NOISES"
• to_title "брат" returns "брат"

• parameter s

  The input string (UTF-8)

• returns

  The title-cased string

to_upper s returns s with all Unicode letters mapped to their upper case.

This function currently only uppercases ASCII letters (a-z). TODO: Support full Unicode uppercasing in the future.

Examples:

• to_upper "Camel" returns "CAMEL"
• to_upper "camel" returns "CAMEL"
• to_upper "こんにちは" returns "こんにちは"

• parameter s

  The input string (UTF-8)

• returns

  The uppercased string

Convert words separated by space, underscore, or hyphen to camel case.

• Words are split on '_', '-', or space.
• The first word is lowercased (even if originally all uppercase).
• Subsequent words are capitalized (first letter uppercase, rest lowercase).
• All-uppercase words are handled (e.g. "GOLANG_IS_GREAT" → "golangIsGreat").
• If there are no separators, the original string is returned (e.g. "alreadyCamel" → "alreadyCamel").
• Leading and trailing underscores are preserved (e.g. "_complex__case_" → "_complexCase_").
• Multiple consecutive separators are treated as a single word boundary.
• Hyphens and spaces are also treated as word boundaries.

Examples:

• to_camel_case "some_words" = "someWords"
• to_camel_case "_complex__case_" = "_complexCase_"
• to_camel_case "OCAML_IS_GREAT" = "ocamlIsGreat"
• to_camel_case "alreadyCamel" = "alreadyCamel"
• to_camel_case "foo-BarBaz" = "fooBarBaz"
• to_camel_case "word" = "word"
• to_camel_case "" = ""

to_kebab_case s converts a string to kebab-case.

• Uppercase ASCII letters are converted to lowercase.
• Word boundaries are detected at transitions from lowercase to uppercase, from letter to digit, and at underscores, spaces, or hyphens.
• All word boundaries are replaced with a single hyphen '-'.
• Multiple consecutive separators are treated as a single hyphen.
• Leading and trailing hyphens are removed.
• If the input is empty, returns the empty string.

Examples:

• to_kebab_case "FirstName" = "first-name"
• to_kebab_case "HTTPServer" = "http-server"
• to_kebab_case "NoHTTPS" = "no-https"
• to_kebab_case "GO_PATH" = "go-path"
• to_kebab_case "GO PATH" = "go-path"
• to_kebab_case "GO-PATH" = "go-path"
• to_kebab_case "http2xx" = "http-2xx"
• to_kebab_case "HTTP20xOK" = "http-20x-ok"
• to_kebab_case "Duration2m3s" = "duration-2m-3s"
• to_kebab_case "Bld4Floor3rd" = "bld4-floor-3rd"
• to_kebab_case "abc" = "abc"
• to_kebab_case "A" = "a"
• to_kebab_case "FooBarBaz" = "foo-bar-baz"
• to_kebab_case "" = ""

Convert words separated by space, underscore, or hyphen to PascalCase.

• Words are split on '_', '-', or space.
• Each word is capitalized (first letter uppercase, rest lowercase).
• All-uppercase words are handled (e.g. "OCAML_IS_GREAT" → "OcamlIsGreat").
• If there are no separators, the first letter is uppercased, the rest are unchanged.
• Leading and trailing underscores and separators are removed in the output.
• Multiple consecutive separators are treated as a single word boundary.
• Hyphens and spaces are also treated as word boundaries. Examples:
• to_pascal_case "some_words" = "SomeWords"
• to_pascal_case "_complex__case_" = "ComplexCase"
• to_pascal_case "OCAML_IS_GREAT" = "OcamlIsGreat"
• to_pascal_case "alreadyPascal" = "AlreadyPascal"
• to_pascal_case "foo-BarBaz" = "FooBarBaz"
• to_pascal_case "word" = "Word"
• to_pascal_case "" = ""

to_snake_case s converts a string to snake_case.

• Uppercase ASCII letters are converted to lowercase.
• Word boundaries are detected at transitions from lowercase to uppercase, from letter to digit, and at underscores, spaces, or hyphens.
• All word boundaries are replaced with a single underscore '_'.
• Multiple consecutive separators are treated as a single underscore.
• Leading and trailing underscores are removed.
• If the input is empty, returns the empty string.

Examples:

• to_snake_case "FirstName" = "first_name"
• to_snake_case "HTTPServer" = "http_server"
• to_snake_case "NoHTTPS" = "no_https"
• to_snake_case "GO_PATH" = "go_path"
• to_snake_case "GO PATH" = "go_path"
• to_snake_case "GO-PATH" = "go_path"
• to_snake_case "http2xx" = "http_2xx"
• to_snake_case "HTTP20xOK" = "http_20x_ok"
• to_snake_case "Duration2m3s" = "duration_2m3s"
• to_snake_case "Bld4Floor3rd" = "bld4_floor_3rd"