Module StringxSource

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