Strings and characters

String is immutable Unicode text. Char is one Unicode code point. They are distinct types: a one-character string is not a Char, and a Char is not an Int even though the JavaScript backend stores its code-point value as a number.

Construct and concatenate text

Quoted strings use "...", characters use single quotes, and ++ concatenates strings:

func greeting(name : String) -> String do
  "Hello, " ++ name ++ "!"
end

Use String.join(values, separator) to combine an array of strings without a manual concatenation loop:

func main() -> Unit do
  Console.println(String.join(["a", "b", "c"], ", "));
end

Explicit conversions

Associated conversion methods include:

• Int.to_string();
• Int.to_double();
• Int64.to_int(), Int64.to_double(), and Int64.to_string();
• Bool.to_int() and Bool.to_string();
• Char.to_int() and Char.to_string();
• Double.to_string().

The reverse direction parses decimal text with an optional sign, answering with an Option that is empty for any other shape: Int.parse(), Int64.parse() (which is also empty outside the 64-bit range), and Double.parse() (which accepts one fraction and one exponent).

Conversions are explicit; context never silently changes one primitive type into another.

Char.from_codepoint(value) constructs a character from an integer code point:

func main() -> Unit do
  character = Char.from_codepoint(0x1f600);
  Console.println(character.to_string());
  Debug.trace(character.to_int());
end

Trim known prefixes and suffixes

trim_prefix(prefix) and trim_suffix(suffix) remove one known edge string. When the string does not start or end with the given text, they return the string unchanged:

func module_basename(filename : String) -> String do
  filename.trim_suffix(".nl")
end

Both operations trim at most one occurrence at the boundary and never scan for repeated matches. Pair them with starts_with / ends_with when the caller needs to know whether a trim happened.

Cursor-based string access

Strings do not expose integer indexing or a code-point length() method. Instead, a StringCursor represents a boundary in one specific string:

func first_character(value : String) -> Option[Char] do
  value.character_at(value.start_cursor())
end

The cursor API includes:

• start_cursor() and end_cursor();
• next_cursor(cursor) and previous_cursor(cursor), returning Option at the boundaries;
• character_at(cursor) and unsafe_character_at(cursor);
• slice(from, to) for a half-open cursor range;
• utf16_distance(from, to) for protocols that need UTF-16 offsets.

A cursor belongs to the string from which it was obtained. Passing it to a different string is outside the API contract.

Iterate by code point

The standard library supplies an iterable provider for String, so foreach visits characters rather than backend UTF-16 code units:

func print_characters(value : String) -> Unit do
  foreach character in value do
    Console.println(character.to_string());
  end;
end

This keeps supplementary Unicode characters such as '😀' as one Char.

Floating-point helpers

The Double view provides sqrt(), pow(exponent), floor_to_int(), and truncate_to_int(). The last two are explicit lossy conversions with different rounding rules; neither is an implicit numeric conversion.

Next: Sorted maps.