@teakit/arith

Use this skill when writing code for @teakit/arith.

@teakit/arith exports Arith, an arbitrary-precision decimal arithmetic API for ESM and browser environments.

Core Rules

Import with import { Arith } from "@teakit/arith".
Do not use default imports from @teakit/arith.
Create values with Arith.from(...); do not use new Arith(...) or call Arith(...).
Static methods such as Arith.config() and Arith.clone() are valid.
Use string inputs for exact decimal values, especially money-like values.
Do not generate BigNumber, Decimal, isBigNumber, or isDecimal.
Do not use JavaScript arithmetic or comparison operators on Arith values.
Use Arith.clone() when precision, rounding, or formatting config must stay local.
Use toFixed() for fixed decimal places and toFormat() for display strings.
Treat Arith instances as immutable. Do not mutate c, e, s, or _isArith.

Identify the operation: creation/configuration, core arithmetic, mathematical functions, rounding/precision/bounds, comparison, predicates, formatting/conversion, allocation, or static utilities.
Load only the relevant method reference file from references/.
In that file, read the intro, inline examples, API Reference, Agent Contract, and Agent Notes before generating code.
Prefer Arith.from(...), exact string inputs, and Arith instance methods in generated code.
If config is needed in reusable code, use a cloned constructor instead of shared Arith.config().
For repository changes, run the local verification commands when relevant: bun run check, bun run typecheck, bun test, and bun run build.
For documentation site changes, also run bun run docs:build.

import { Arith } from "@teakit/arith";

const total = Arith.from("0.1").add("0.2");
total.toString(); // "0.3"

Read the smallest method file that answers the current task. Do not load every reference file unless the user asks for a full API audit.

Need	Prefer
Exact decimal math	`Arith.from("0.1")`, then instance methods
Explicit ratios	`Arith.fromRatio("1/3")` or `Arith.ratio("1", "3")`
Local money config	`const Money = Arith.clone({ DECIMAL_PLACES: 2 })`
Deterministic splits	`Arith.allocate(total, weights, options?)`
Array statistics	`Arith.mean(values)`, `Arith.quantile(values, q)`, or `Arith.std(values)`
Comparisons	`cmp`, `eq`, `ne`, `gt`, `ge`, `lt`, or `le`
Fixed output	`toFixed(decimalPlaces, roundingMode?)`
Human display	`toFormat(decimalPlaces?, roundingMode?, options?)`
JSON output	`JSON.stringify` uses `toJSON()` automatically
Browser use	Import from `@teakit/arith`; do not add Node runtime imports