JavaScript interface

JavaScript features are accessible via JavaScript structure.

ES modules can be imported with _esImport declaration: Importing ECMAScript Modules.

ES export

To produce an ES module, use --lib compiler option and define a variable or structure named export.

For example,

val export = <some value>;

will compile to

export default <some value>;

and

structure export = struct
  val foo = "string"
  val bar = 42
  val fun' = "fun" (* SML keywords can be escaped by suffixing with a prime *)
end

will compile to:

const foo = "string";
const bar = 42;
const fun = "fun";
export { foo, bar, fun };

Note on CPS mode: You cannot call certain functions including print at top-level, because they are “async”. In future, this limitation may be lifted by using top-level await.

Internal representation

Warning: The internal representation of data types may change in the future. Do not rely on it!

unit (empty record): undefined.
bool: JavaScript’s boolean; true or false.
int: 54-bit signed integer, as a subset of Number. Overflows are always checked.
word: 32-bit unsigned integer, as a subset of Number. The sign of zero must be positive.
real: 64-bit floating-point number (JavaScript’s native Number).
char: 8-bit unsigned integer. The sign of zero must be positive.
string: Uint8Array. Must not be modified.
WideChar.char: 16-bit unsigned integer. The sign of zero must be positive.
WideString.string: 16-bit string (JavaScript’s native String).
Int54.int: 54-bit signed integer, as a subset of Number (close to “safe integer”). The range is \([-2^{53},2^{53}-1]\). The sign of zero may be negative. Overflows are always checked.
Int64.int: BigInt. Overflows are always checked.
IntInf.int: BigInt.
Word64.word: BigInt.
'a vector: Array. Must not be modified.
'a array: Array.
JavaScript.value: Any JavaScript value, including undefined or null.
Non-empty record: { "0": <#1 of the record>, "foo": <#foo of the record> }