My understanding of where we got to in post-meeting discussions this week with Jesse and nicolo-ribaudo is that an Amount ought to hold a mathematical value (as defined in '262), parsed from a string input value using the same method as for ToIntlMathematicalValue ( value ), but without support for non-finite values or -0. Amount would either have no built-in limits on the value, or it would match the limits imposed by Intl.NumberFormat.

Overall, the intent would be to avoid defining a new numeric type beyond what's already in the spec, even if not easily accessible by users.

During lunch today I joked about defining a tagged template literal for Decimal, but tbh it doesn't look too bad. Here's one of the Decimal readme examples:

function calculateBill(items, tax) {
  let total = Decimal`0`;
  for (let { price, count } of items) {
    total = Decimal`${total} + ${price} * ${count}`;
  }
  return Decimal`${total} * (${tax} + 1)`;
}

You presumably meant this?

m`1.2` !== 1.2m

I think it would be cool to have a decimal-based template syntax, where everything gets converted into a decimal.

let a = new Decimal("1");
let b = "2";
let c = 3;
let d = Decimal`a + b + c`; // 6

We don't need to add Decimal if:

let a = 0.1;
D`${a} + 0.2` === 0.3

desugars to:

let a = 0.1;
Math.decimalAdd(a, 0.2) === 0.3

Basically I think there needs to be a cohesive statement about why we think Decimal solves the problem statement better than Math.decimalAdd, if we believe that it does.

(Also, we never got around to updating the problem statement. The README is still out of date.)