money.compare

export function compareMoney(a: Money, b: Money): number

import { compareMoney } from "#fune/money.compare@^1";

import { clamp } from "./math_clamp.ts";  ← from math.clamp ^1.0.0 · built alongside by fune
import { type Money, assertSameCurrency, money } from "./money_amount.ts";  ← from money.amount ^1.0.0 · built alongside by fune

/**
 * -1, 0 or 1, comparing two amounts of the same currency.
 *
 * Refuses mixed currencies: which of GBP 10 and EUR 10 is larger depends on a
 * rate, and a comparison that ignores the currency sorts a list into nonsense.
 */
export function compareMoney(a: Money, b: Money): number {
  assertSameCurrency(a, b);
  return a.minor < b.minor ? -1 : a.minor > b.minor ? 1 : 0;
}

/** The smaller amount; the first when they are equal. */
export function minMoney(a: Money, b: Money): Money {
  return compareMoney(b, a) < 0 ? b : a;
}

/** The larger amount; the first when they are equal. */
export function maxMoney(a: Money, b: Money): Money {
  return compareMoney(b, a) > 0 ? b : a;
}

/** `amount` held within `min..max`, all three in one currency. */
export function clampMoney(amount: Money, min: Money, max: Money): Money {
  assertSameCurrency(amount, min);
  assertSameCurrency(amount, max);
  return money(clamp(amount.minor, min.minor, max.minor), amount.currency);
}

Install

fune build

With that line in your source, in a TypeScript project (language typescript in fune.project), fune build resolves it and its 2 dependencies, pins them in fune.lock, downloads only the TypeScript package of each, and builds the code above into your project’s .fune/build, one readable file per capability with a header linking back here. Or pin a range in fune.project and build in one step:

fune add money.compare

The manifest, vectors and README with only the TypeScript implementation. Install it without the registry with fune add ./money.compare-1.0.0-typescript.fune, or fetch it from a terminal with fune pull money.compare@1.0.0:typescript.

The whole function, every language, is one file too: money.compare-1.0.0.fune, 9,081 bytes, sha256 a2f90e08a0b24b24f121a1d6df2604bc4d7f49028d1aeeaf71dcd14cd8162520. It installs into a project of any language.

// fune: before money.compare

// fune: after money.compare

// fune: replace math.clamp in money.compare
// fune: replace money.amount in money.compare

// fune: step money.compare after <n|label>

More from the author

The module also exports `minMoney(a, b)`, `maxMoney(a, b)` and `clampMoney(amount, min, max)`, built on `compareMoney` and `math.clamp` with the same currency check. `minMoney` and `maxMoney` return the first argument when the two are equal. `clampMoney` refuses a range whose `min` is above its `max`, as `math.clamp` does: capping a refund at the original charge, or a discount at the order total, with the bounds the wrong way round is a bug to surface, not a value to return.

Files