{
  "id": "investments",
  "title": "Investments and wealth",
  "summary": "Portfolios and wealth: returns (TWR, XIRR, CAGR), weights and rebalancing, fees, yields, bonds, drawdown, and UK ISA, pension and capital gains tax.",
  "synonyms": [
    "investments",
    "investing",
    "wealth management",
    "portfolio",
    "portfolio tracker",
    "stocks and shares",
    "funds",
    "ISA",
    "pension",
    "SIPP",
    "capital gains tax",
    "robo advisor",
    "financial planning"
  ],
  "apps": [
    "portfolio tracker",
    "wealth management platform",
    "robo-advisor",
    "investment app",
    "financial planning tool",
    "pension drawdown calculator",
    "share dealing app"
  ],
  "language": "rust",
  "includes": [
    "money-basics",
    "dates-basics",
    "uk-tax"
  ],
  "includedBy": [],
  "caveats": [
    "Not financial or tax advice. ISA, pension and capital gains tax rules are UK and dated; regulated advice needs a qualified adviser.",
    "Calculates tax from published rules; it is not tax advice. Have an accountant check how the app uses it before anyone files a return."
  ],
  "sections": [
    {
      "key": "performance",
      "title": "Performance",
      "purpose": "Report how a portfolio has done.",
      "from": "investments",
      "members": [
        {
          "id": "invest.time-weighted-return",
          "tier": "core",
          "why": "Time-weighted return from valuations at each external cash flow, for comparing managers.",
          "section": "performance",
          "from": "investments",
          "version": "1.0.1",
          "summary": "Time-weighted return from valuations taken at each external cash flow, geometrically linked exactly.",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "timeWeightedReturn"
          ],
          "signatures": [
            "pub fn time_weighted_return(points: &[ValuationPoint]) -> TwrResult"
          ],
          "reference": "fune!(invest.time-weighted-return@^1);  // then call time_weighted_return(…)",
          "url": "http://www.functionalweave.com/functions/invest.time-weighted-return"
        },
        {
          "id": "invest.money-weighted-return",
          "tier": "core",
          "why": "Money-weighted return (XIRR) of dated cash flows, what the investor actually earned.",
          "section": "performance",
          "from": "investments",
          "version": "1.0.1",
          "summary": "Money-weighted return (XIRR) of dated cash flows on Excel's actual/365 convention, solved exactly in fixed point.",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "moneyWeightedReturn"
          ],
          "signatures": [
            "pub fn money_weighted_return(flows: &[DatedFlow]) -> XirrResult"
          ],
          "reference": "fune!(invest.money-weighted-return@^1);  // then call money_weighted_return(…)",
          "url": "http://www.functionalweave.com/functions/invest.money-weighted-return"
        },
        {
          "id": "invest.cagr",
          "tier": "optional",
          "why": "Compound annual growth rate between two values over whole or fractional years.",
          "section": "performance",
          "from": "investments",
          "version": "1.0.1",
          "summary": "Compound annual growth rate between two values over a whole or fractional number of years, in basis points.",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "cagr"
          ],
          "signatures": [
            "pub fn cagr(start_value: &Money, end_value: &Money, years_numerator: i64, years_denominator: i64) -> i64"
          ],
          "reference": "fune!(invest.cagr@^1);  // then call cagr(…)",
          "url": "http://www.functionalweave.com/functions/invest.cagr"
        },
        {
          "id": "math.percent-change",
          "tier": "optional",
          "why": "Percentage change between two values, for daily and period moves.",
          "section": "performance",
          "from": "investments",
          "version": "1.0.0",
          "summary": "Percentage change from one value to another, in basis points, with an explicit rounding mode.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "percentChange"
          ],
          "signatures": [
            "pub fn percent_change(from_value: i64, to_value: i64, mode: &RoundingMode) -> Option<i64>"
          ],
          "reference": "fune!(math.percent-change@^1);  // then call percent_change(…)",
          "url": "http://www.functionalweave.com/functions/math.percent-change"
        }
      ],
      "gaps": []
    },
    {
      "key": "portfolio",
      "title": "Holdings and rebalancing",
      "purpose": "Show what a portfolio holds and bring it back to target.",
      "from": "investments",
      "members": [
        {
          "id": "invest.portfolio-weights",
          "tier": "core",
          "why": "Each holding's share of the portfolio and its drift from target, in basis points.",
          "section": "portfolio",
          "from": "investments",
          "version": "1.0.1",
          "summary": "Each holding's share of a portfolio and its drift from a target weight, in basis points, from exact arithmetic.",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "portfolioWeights"
          ],
          "signatures": [
            "pub fn portfolio_weights(holdings: &[PortfolioHolding]) -> PortfolioWeights"
          ],
          "reference": "fune!(invest.portfolio-weights@^1);  // then call portfolio_weights(…)",
          "url": "http://www.functionalweave.com/functions/invest.portfolio-weights"
        },
        {
          "id": "invest.rebalance",
          "tier": "core",
          "why": "Whole-unit buy and sell trades back to target weights, skipping trades below a minimum.",
          "section": "portfolio",
          "from": "investments",
          "version": "1.0.1",
          "summary": "Whole-unit buy and sell trades that bring a portfolio back to target weights, skipping trades below a minimum size.",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "rebalance"
          ],
          "signatures": [
            "pub fn rebalance(holdings: &[RebalanceHolding], cash: &Money, minimum_trade: &Money) -> RebalancePlan"
          ],
          "reference": "fune!(invest.rebalance@^1);  // then call rebalance(…)",
          "url": "http://www.functionalweave.com/functions/invest.rebalance"
        }
      ],
      "gaps": [
        {
          "key": "market-data",
          "text": "Prices, fund data and corporate actions come from a market data provider.",
          "section": "portfolio",
          "from": "investments"
        },
        {
          "key": "order-execution",
          "text": "Placing trades with a broker or custodian (and settlement) is not in caps.",
          "section": "portfolio",
          "from": "investments"
        }
      ]
    },
    {
      "key": "income",
      "title": "Income and costs",
      "purpose": "Show yields and what charges cost.",
      "from": "investments",
      "members": [
        {
          "id": "invest.dividend-yield",
          "tier": "optional",
          "why": "Trailing and forward dividend yield of a share or fund.",
          "section": "income",
          "from": "investments",
          "version": "1.0.1",
          "summary": "Trailing and forward dividend yield of a share or fund, in basis points, from the price and the dividends per unit.",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "dividendYield"
          ],
          "signatures": [
            "pub fn dividend_yield(price: &Money, trailing_dividends: &[Money], forward_dividend: &Money, payments_per_year: i64) -> DividendYield"
          ],
          "reference": "fune!(invest.dividend-yield@^1);  // then call dividend_yield(…)",
          "url": "http://www.functionalweave.com/functions/invest.dividend-yield"
        },
        {
          "id": "invest.bond-yield",
          "tier": "optional",
          "why": "Current yield and yield to maturity of a fixed-coupon bond.",
          "section": "income",
          "from": "investments",
          "version": "1.0.2",
          "summary": "Current yield and yield to maturity of a fixed-coupon bond from its clean price, as Excel's YIELD defines it.",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "bondYield"
          ],
          "signatures": [
            "pub fn bond_yield(settlement: &str, maturity: &str, coupon_basis_points: i64, clean_price: &str, frequency: i64, basis: &str) -> BondYield"
          ],
          "reference": "fune!(invest.bond-yield@^1);  // then call bond_yield(…)",
          "url": "http://www.functionalweave.com/functions/invest.bond-yield"
        },
        {
          "id": "invest.fee-drag",
          "tier": "optional",
          "why": "What an annual charge costs over the years, with and without the fee.",
          "section": "income",
          "from": "investments",
          "version": "1.0.1",
          "summary": "What an annual charge costs an investment over the years: value with and without the fee, year by year, in minor units.",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "feeDrag"
          ],
          "signatures": [
            "pub fn fee_drag(start_value: &Money, annual_growth_basis_points: i64, annual_fee_basis_points: i64, years: i64) -> FeeDrag"
          ],
          "reference": "fune!(invest.fee-drag@^1);  // then call fee_drag(…)",
          "url": "http://www.functionalweave.com/functions/invest.fee-drag"
        }
      ],
      "gaps": []
    },
    {
      "key": "planning",
      "title": "Planning and retirement",
      "purpose": "Project how long money lasts.",
      "from": "investments",
      "members": [
        {
          "id": "invest.drawdown-sustainability",
          "tier": "optional",
          "why": "How many years a pot lasts under a withdrawal and growth rate.",
          "section": "planning",
          "from": "investments",
          "version": "1.0.1",
          "summary": "How many years a pension or investment pot lasts under a yearly withdrawal and a constant growth rate, year by year.",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "drawdownSustainability"
          ],
          "signatures": [
            "pub fn drawdown_sustainability(pot: &Money, annual_withdrawal: &Money, annual_growth_basis_points: i64, withdrawal_increase_basis_points: i64, max_years: i64) -> Drawdown"
          ],
          "reference": "fune!(invest.drawdown-sustainability@^1);  // then call drawdown_sustainability(…)",
          "url": "http://www.functionalweave.com/functions/invest.drawdown-sustainability"
        },
        {
          "id": "finance.compound-interest",
          "tier": "optional",
          "why": "Compound growth period by period, for savings projections.",
          "section": "planning",
          "from": "investments",
          "version": "1.0.0",
          "summary": "Compound interest accrued period by period in minor units, the way a statement is built.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "compoundInterest"
          ],
          "signatures": [
            "pub fn compound_interest(principal: &Money, annual_rate_basis_points: i64, periods_per_year: i64, years: i64) -> CompoundInterestResult"
          ],
          "reference": "fune!(finance.compound-interest@^1);  // then call compound_interest(…)",
          "url": "http://www.functionalweave.com/functions/finance.compound-interest"
        }
      ],
      "gaps": [
        {
          "key": "cashflow-modelling",
          "text": "Stochastic (Monte Carlo) and lifetime cash-flow modelling are not in caps.",
          "section": "planning",
          "from": "investments"
        }
      ]
    },
    {
      "key": "tax",
      "title": "Tax wrappers and gains",
      "purpose": "Track allowances and work out tax on gains.",
      "from": "investments",
      "members": [
        {
          "id": "invest.isa-allowance",
          "tier": "core",
          "why": "ISA allowance used and remaining for a tax year, including Lifetime, cash and Junior ISAs.",
          "section": "tax",
          "from": "investments",
          "version": "1.0.2",
          "summary": "ISA allowance used and remaining for a UK tax year: the overall limit, Lifetime ISA, cash ISA and Junior ISA.",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "isaAllowance"
          ],
          "signatures": [
            "pub fn isa_allowance(tax_year_date: &str, subscriptions: &[IsaSubscription], date_of_birth: Option<&str>) -> IsaAllowance"
          ],
          "reference": "fune!(invest.isa-allowance@^1);  // then call isa_allowance(…)",
          "url": "http://www.functionalweave.com/functions/invest.isa-allowance"
        },
        {
          "id": "invest.capital-gains-tax",
          "tier": "optional",
          "why": "UK Capital Gains Tax for a tax year: losses, annual exempt amount and rates.",
          "section": "tax",
          "from": "investments",
          "version": "1.0.1",
          "summary": "UK Capital Gains Tax for an individual's tax year: losses, annual exempt amount, and the rates by asset and date.",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "capitalGainsTax"
          ],
          "signatures": [
            "pub fn capital_gains_tax(tax_year_date: &str, disposals: &[CgtDisposal], taxable_income: &Money, losses_brought_forward: &Money) -> CgtResult"
          ],
          "reference": "fune!(invest.capital-gains-tax@^1);  // then call capital_gains_tax(…)",
          "url": "http://www.functionalweave.com/functions/invest.capital-gains-tax"
        },
        {
          "id": "invest.section-104-pool",
          "tier": "optional",
          "why": "UK share matching for CGT: same-day, 30-day and Section 104 pool cost per disposal.",
          "section": "tax",
          "from": "investments",
          "version": "1.0.1",
          "summary": "UK share matching for CGT: same-day, 30-day bed-and-breakfast, then the Section 104 pool; allowable cost per disposal.",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "section104Pool"
          ],
          "signatures": [
            "pub fn section104_pool(transactions: &[ShareTransaction]) -> Section104Result"
          ],
          "reference": "fune!(invest.section-104-pool@^1);  // then call section104_pool(…)",
          "url": "http://www.functionalweave.com/functions/invest.section-104-pool"
        },
        {
          "id": "invest.pension-annual-allowance",
          "tier": "optional",
          "why": "Pension annual allowance with taper, MPAA and carry-forward, and the excess charged.",
          "section": "tax",
          "from": "investments",
          "version": "1.0.1",
          "summary": "UK pension annual allowance for a tax year with taper, MPAA and three-year carry-forward, and the excess charged.",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "pensionAnnualAllowance"
          ],
          "signatures": [
            "pub fn pension_annual_allowance(tax_year_date: &str, current: &PensionInputYear, previous_years: &[PensionInputYear]) -> AnnualAllowanceResult"
          ],
          "reference": "fune!(invest.pension-annual-allowance@^1);  // then call pension_annual_allowance(…)",
          "url": "http://www.functionalweave.com/functions/invest.pension-annual-allowance"
        }
      ],
      "gaps": []
    },
    {
      "key": "charts",
      "title": "Charts",
      "purpose": "Draw portfolio value and allocation.",
      "from": "investments",
      "members": [
        {
          "id": "charts.line-chart",
          "tier": "optional",
          "why": "Line chart geometry for value over time.",
          "section": "charts",
          "from": "investments",
          "version": "1.0.0",
          "summary": "Complete line chart geometry as data: plot area, number or date axes, gridlines, series paths, colours, legend.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "lineChart"
          ],
          "signatures": [
            "pub fn line_chart(spec: &LineChartSpec) -> LineChart"
          ],
          "reference": "fune!(charts.line-chart@^1);  // then call line_chart(…)",
          "url": "http://www.functionalweave.com/functions/charts.line-chart"
        },
        {
          "id": "charts.shape",
          "tier": "optional",
          "why": "Pie or donut slices for an allocation chart.",
          "section": "charts",
          "from": "investments",
          "only": [
            "pieAngles",
            "arcPath"
          ],
          "version": "1.0.1",
          "summary": "SVG path strings for lines, areas, steps, monotone curves, bars, arcs and pie slices, identical in every language.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": true,
          "functions": [
            "arcPath",
            "pieAngles"
          ],
          "signatures": [
            "pub fn arc_path(arc: &Arc) -> String",
            "pub fn pie_angles(values: &[f64], start_angle: f64, end_angle: f64, pad_angle: f64) -> Vec<PieSlice>"
          ],
          "reference": "fune!(charts.shape@^1);  // then call arc_path, pie_angles",
          "url": "http://www.functionalweave.com/functions/charts.shape"
        }
      ],
      "gaps": []
    },
    {
      "key": "amounts",
      "title": "Amounts",
      "purpose": "Hold money as currency-tagged integer minor units and do plain arithmetic on it safely.",
      "from": "money-basics",
      "members": [
        {
          "id": "money.amount",
          "tier": "core",
          "why": "The Money type ({ minor, currency }) every other money capability takes and returns.",
          "section": "amounts",
          "from": "money-basics",
          "version": "1.0.2",
          "summary": "A currency-tagged monetary amount held in integer minor units.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "money"
          ],
          "signatures": [
            "pub fn money(minor: i64, currency: &str) -> Money"
          ],
          "reference": "fune!(money.amount@^1);  // then call money(…)",
          "url": "http://www.functionalweave.com/functions/money.amount"
        },
        {
          "id": "money.add",
          "tier": "core",
          "why": "Adds and subtracts amounts, refusing to mix currencies by accident.",
          "section": "amounts",
          "from": "money-basics",
          "version": "1.0.1",
          "summary": "Add, subtract and negate monetary amounts, refusing to mix currencies.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "addMoney"
          ],
          "signatures": [
            "pub fn add_money(a: &Money, b: &Money) -> Money"
          ],
          "reference": "fune!(money.add@^1);  // then call add_money(…)",
          "url": "http://www.functionalweave.com/functions/money.add"
        },
        {
          "id": "money.sum",
          "tier": "core",
          "why": "Totals a list of amounts, with an explicit currency for an empty list.",
          "section": "amounts",
          "from": "money-basics",
          "version": "1.0.1",
          "summary": "Total a list of monetary amounts, with an explicit currency for the empty case.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "sumMoney"
          ],
          "signatures": [
            "pub fn sum_money(amounts: &[Money], currency: &str) -> Money"
          ],
          "reference": "fune!(money.sum@^1);  // then call sum_money(…)",
          "url": "http://www.functionalweave.com/functions/money.sum"
        },
        {
          "id": "money.compare",
          "tier": "core",
          "why": "Compares, mins, maxes and clamps amounts of one currency without unwrapping them.",
          "section": "amounts",
          "from": "money-basics",
          "version": "2.0.0",
          "summary": "Compare two amounts of one currency, refusing to compare across currencies; min, max and clamp too.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": true,
          "functions": [
            "compareMoney",
            "minMoney",
            "maxMoney",
            "clampMoney"
          ],
          "signatures": [
            "pub fn compare_money(a: &Money, b: &Money) -> i64",
            "pub fn min_money(a: &Money, b: &Money) -> Money",
            "pub fn max_money(a: &Money, b: &Money) -> Money",
            "pub fn clamp_money(amount: &Money, min: &Money, max: &Money) -> Money"
          ],
          "reference": "fune!(money.compare@^2);  // then call compare_money, min_money, max_money, clamp_money",
          "url": "http://www.functionalweave.com/functions/money.compare"
        }
      ],
      "gaps": []
    },
    {
      "key": "rates",
      "title": "Rates and rounding",
      "purpose": "Apply percentages and divide amounts with the rounding stated, never a float.",
      "from": "money-basics",
      "members": [
        {
          "id": "money.apply-rate",
          "tier": "core",
          "why": "Applies a basis-point rate (VAT, discount, commission) to an amount with explicit rounding.",
          "section": "rates",
          "from": "money-basics",
          "version": "1.0.1",
          "summary": "Apply a rate expressed in basis points to a monetary amount, with an explicit rounding mode.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "applyRate"
          ],
          "signatures": [
            "pub fn apply_rate(amount: &Money, basis_points: i64, mode: &RoundingMode) -> Money"
          ],
          "reference": "fune!(money.apply-rate@^1);  // then call apply_rate(…)",
          "url": "http://www.functionalweave.com/functions/money.apply-rate"
        },
        {
          "id": "math.round-div",
          "tier": "core",
          "why": "Integer division with a named rounding mode, for any money maths the others do not cover.",
          "section": "rates",
          "from": "money-basics",
          "version": "1.0.0",
          "summary": "Integer division with an explicit rounding mode, for money arithmetic that must not drift.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "roundDiv"
          ],
          "signatures": [
            "pub fn round_div(numerator: i64, denominator: i64, mode: &str) -> i64"
          ],
          "reference": "fune!(math.round-div@^1);  // then call round_div(…)",
          "url": "http://www.functionalweave.com/functions/math.round-div"
        },
        {
          "id": "math.basis-points",
          "tier": "optional",
          "why": "Converts \"12.5%\" to and from basis points exactly, for rates typed in by users.",
          "section": "rates",
          "from": "money-basics",
          "version": "2.0.0",
          "summary": "Convert a rate between percent, basis points and a plain ratio exactly, as decimal text or integer basis points.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": true,
          "functions": [
            "convertRate",
            "toBasisPoints",
            "fromBasisPoints"
          ],
          "signatures": [
            "pub fn convert_rate(value: &str, from_unit: &str, to_unit: &str) -> String",
            "pub fn to_basis_points(value: &str, unit: &str) -> i64",
            "pub fn from_basis_points(basis_points: i64, unit: &str) -> String"
          ],
          "reference": "fune!(math.basis-points@^2);  // then call convert_rate, to_basis_points, from_basis_points",
          "url": "http://www.functionalweave.com/functions/math.basis-points"
        },
        {
          "id": "math.rational",
          "tier": "optional",
          "why": "Exact fractions for rates that must not drift across many steps.",
          "section": "rates",
          "from": "money-basics",
          "version": "2.0.0",
          "summary": "Exact fraction arithmetic, always reduced, for rates and ratios that must not drift.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": true,
          "functions": [
            "calculateRational",
            "rational",
            "addRational",
            "subtractRational",
            "multiplyRational",
            "divideRational",
            "compareRational",
            "rationalToInteger"
          ],
          "signatures": [
            "pub fn calculate_rational(a: &Rational, op: &str, b: &Rational) -> Rational",
            "pub fn rational(numerator: i64, denominator: i64) -> Rational",
            "pub fn add_rational(a: &Rational, b: &Rational) -> Rational",
            "pub fn subtract_rational(a: &Rational, b: &Rational) -> Rational",
            "pub fn multiply_rational(a: &Rational, b: &Rational) -> Rational",
            "pub fn divide_rational(a: &Rational, b: &Rational) -> Rational",
            "pub fn compare_rational(a: &Rational, b: &Rational) -> i64",
            "pub fn rational_to_integer(r: &Rational, mode: &RoundingMode) -> i64"
          ],
          "reference": "fune!(math.rational@^2);  // then call calculate_rational, rational, add_rational, subtract_rational, multiply_rational, divide_rational, compare_rational, rational_to_integer",
          "url": "http://www.functionalweave.com/functions/math.rational"
        },
        {
          "id": "math.round-div-big",
          "tier": "optional",
          "why": "Rounded division on numbers past 2^53, for very large totals.",
          "section": "rates",
          "from": "money-basics",
          "version": "1.0.0",
          "summary": "Divide two integers of any size with an explicit rounding mode, on decimal strings, for exact money sums past 2^53.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "roundDivBig"
          ],
          "signatures": [
            "pub fn round_div_big(numerator: &str, denominator: &str, mode: &RoundingMode) -> String"
          ],
          "reference": "fune!(math.round-div-big@^1);  // then call round_div_big(…)",
          "url": "http://www.functionalweave.com/functions/math.round-div-big"
        }
      ],
      "gaps": []
    },
    {
      "key": "splitting",
      "title": "Splitting",
      "purpose": "Divide an amount between people, periods or lines so the parts add back to the whole.",
      "from": "money-basics",
      "members": [
        {
          "id": "money.allocate",
          "tier": "core",
          "why": "Splits an amount by ratios (60/40, by quantity) without losing or inventing a penny.",
          "section": "splitting",
          "from": "money-basics",
          "version": "1.0.1",
          "summary": "Split an amount across ratios without losing or inventing a single minor unit.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "allocate"
          ],
          "signatures": [
            "pub fn allocate(amount: &Money, ratios: &[i64]) -> Vec<Money>"
          ],
          "reference": "fune!(money.allocate@^1);  // then call allocate(…)",
          "url": "http://www.functionalweave.com/functions/money.allocate"
        },
        {
          "id": "money.split-even",
          "tier": "optional",
          "why": "Splits an amount into n near-equal parts that sum exactly, for instalments or shares.",
          "section": "splitting",
          "from": "money-basics",
          "version": "1.0.0",
          "summary": "Split an amount into n near-equal parts that add back up to exactly the whole.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "splitEven"
          ],
          "signatures": [
            "pub fn split_even(amount: &Money, parts: i64) -> Vec<Money>"
          ],
          "reference": "fune!(money.split-even@^1);  // then call split_even(…)",
          "url": "http://www.functionalweave.com/functions/money.split-even"
        }
      ],
      "gaps": []
    },
    {
      "key": "display",
      "title": "Display and input",
      "purpose": "Show amounts to people and read what they type.",
      "from": "money-basics",
      "members": [
        {
          "id": "money.format",
          "tier": "core",
          "why": "Renders an amount as text with the currency's real number of decimal places.",
          "section": "display",
          "from": "money-basics",
          "version": "1.0.0",
          "summary": "Render a monetary amount as text, using the currency's real minor-unit precision.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "formatMoney"
          ],
          "signatures": [
            "pub fn format_money(amount: &Money) -> String"
          ],
          "reference": "fune!(money.format@^1);  // then call format_money(…)",
          "url": "http://www.functionalweave.com/functions/money.format"
        },
        {
          "id": "money.parse",
          "tier": "optional",
          "why": "Reads \"£1,234.50\" or \"1.234,50 €\" typed by a user into minor units, strictly.",
          "section": "display",
          "from": "money-basics",
          "version": "1.0.0",
          "summary": "Parse \"£1,234.50\" or \"1.234,50 €\" into integer minor units, strictly: no guessing, no rounding.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "parseMoney"
          ],
          "signatures": [
            "pub fn parse_money(text: &str, currency: &str, style: &str) -> Money"
          ],
          "reference": "fune!(money.parse@^1);  // then call parse_money(…)",
          "url": "http://www.functionalweave.com/functions/money.parse"
        },
        {
          "id": "money.currency-digits",
          "tier": "optional",
          "why": "How many decimal places each ISO 4217 currency has, for input boxes and validation.",
          "section": "display",
          "from": "money-basics",
          "version": "1.0.0",
          "summary": "How many decimal places a currency's minor unit has, from the ISO 4217 list.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "currencyDigits"
          ],
          "signatures": [
            "pub fn currency_digits(currency: &str) -> i64"
          ],
          "reference": "fune!(money.currency-digits@^1);  // then call currency_digits(…)",
          "url": "http://www.functionalweave.com/functions/money.currency-digits"
        }
      ],
      "gaps": []
    },
    {
      "key": "currencies",
      "title": "Other currencies",
      "purpose": "Convert between currencies at a rate you hold.",
      "from": "money-basics",
      "members": [
        {
          "id": "money.convert",
          "tier": "optional",
          "why": "Converts an amount at a supplied exact rate with explicit rounding.",
          "section": "currencies",
          "from": "money-basics",
          "version": "1.0.0",
          "summary": "Convert an amount to another currency at a supplied exact rate, with an explicit rounding mode.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "convertMoney"
          ],
          "signatures": [
            "pub fn convert_money(amount: &Money, rate: &ExchangeRate, mode: &RoundingMode) -> Money"
          ],
          "reference": "fune!(money.convert@^1);  // then call convert_money(…)",
          "url": "http://www.functionalweave.com/functions/money.convert"
        }
      ],
      "gaps": []
    },
    {
      "key": "date-arithmetic",
      "title": "Calendar arithmetic",
      "purpose": "Move and measure ISO dates exactly, with no date library and no clock reads.",
      "from": "dates-basics",
      "members": [
        {
          "id": "dates.add-days",
          "tier": "core",
          "why": "Shifts a date by whole days, for due dates and windows.",
          "section": "date-arithmetic",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "Shift an ISO date by a whole number of days, forwards or backwards, with exact calendar arithmetic.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "addDays"
          ],
          "signatures": [
            "pub fn add_days(iso: &str, days: i64) -> String"
          ],
          "reference": "fune!(dates.add-days@^1);  // then call add_days(…)",
          "url": "http://www.functionalweave.com/functions/dates.add-days"
        },
        {
          "id": "dates.add-months",
          "tier": "core",
          "why": "Adds months clamping to month end, so 31 January plus a month is the end of February.",
          "section": "date-arithmetic",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "Add calendar months to an ISO date, clamping to the month end: 31 Jan + 1 month is 28 or 29 Feb.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "addMonths"
          ],
          "signatures": [
            "pub fn add_months(iso: &str, months: i64) -> String"
          ],
          "reference": "fune!(dates.add-months@^1);  // then call add_months(…)",
          "url": "http://www.functionalweave.com/functions/dates.add-months"
        },
        {
          "id": "dates.days-between",
          "tier": "core",
          "why": "Signed calendar days between two dates, for ages of invoices and stays.",
          "section": "date-arithmetic",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "Calendar days from one ISO date to another, signed: negative when the second date is earlier.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "daysBetween"
          ],
          "signatures": [
            "pub fn days_between(start_iso: &str, end_iso: &str) -> i64"
          ],
          "reference": "fune!(dates.days-between@^1);  // then call days_between(…)",
          "url": "http://www.functionalweave.com/functions/dates.days-between"
        },
        {
          "id": "dates.month-boundaries",
          "tier": "core",
          "why": "First and last day of a date's month, for monthly periods and statements.",
          "section": "date-arithmetic",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "The first day, last day and length of the calendar month containing a date.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "monthBoundaries"
          ],
          "signatures": [
            "pub fn month_boundaries(iso: &str) -> MonthBoundaries"
          ],
          "reference": "fune!(dates.month-boundaries@^1);  // then call month_boundaries(…)",
          "url": "http://www.functionalweave.com/functions/dates.month-boundaries"
        },
        {
          "id": "dates.day-of-week",
          "tier": "core",
          "why": "ISO weekday of a date, for weekend rules and opening hours.",
          "section": "date-arithmetic",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "The ISO 8601 day of the week for a date: 1 is Monday through 7 is Sunday.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "dayOfWeek"
          ],
          "signatures": [
            "pub fn day_of_week(iso: &str) -> i64"
          ],
          "reference": "fune!(dates.day-of-week@^1);  // then call day_of_week(…)",
          "url": "http://www.functionalweave.com/functions/dates.day-of-week"
        },
        {
          "id": "dates.is-leap-year",
          "tier": "optional",
          "why": "Whether a year is a leap year, for 365/366-day calculations.",
          "section": "date-arithmetic",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "Whether a year is a Gregorian leap year: every 4th, except centuries, except every 400th.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "isLeapYear"
          ],
          "signatures": [
            "pub fn is_leap_year(year: i64) -> bool"
          ],
          "reference": "fune!(dates.is-leap-year@^1);  // then call is_leap_year(…)",
          "url": "http://www.functionalweave.com/functions/dates.is-leap-year"
        },
        {
          "id": "dates.overlap",
          "tier": "optional",
          "why": "Days two date ranges share, for prorating and clash checks.",
          "section": "date-arithmetic",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "Days two date ranges have in common, with the end of each range stated as inclusive or exclusive.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "overlapDays"
          ],
          "signatures": [
            "pub fn overlap_days(a_start: &str, a_end: &str, b_start: &str, b_end: &str, end_inclusive: bool) -> i64"
          ],
          "reference": "fune!(dates.overlap@^1);  // then call overlap_days(…)",
          "url": "http://www.functionalweave.com/functions/dates.overlap"
        },
        {
          "id": "dates.age",
          "tier": "optional",
          "why": "Age in whole years on a date, handling 29 February birthdays.",
          "section": "date-arithmetic",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "Age in whole years on a given date, with 29 February birthdays ageing on 1 March in other years.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "age"
          ],
          "signatures": [
            "pub fn age(birth_date: &str, on_date: &str) -> i64"
          ],
          "reference": "fune!(dates.age@^1);  // then call age(…)",
          "url": "http://www.functionalweave.com/functions/dates.age"
        }
      ],
      "gaps": []
    },
    {
      "key": "reporting-periods",
      "title": "Periods and reporting dates",
      "purpose": "Put dates into the periods reports are grouped by.",
      "from": "dates-basics",
      "members": [
        {
          "id": "dates.quarter",
          "tier": "core",
          "why": "Calendar and fiscal quarter of a date for any year-start month.",
          "section": "reporting-periods",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "Calendar quarter and fiscal quarter of a date, with the fiscal year and quarter date ranges, for any start month.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "quarter"
          ],
          "signatures": [
            "pub fn quarter(iso: &str, fiscal_year_start_month: i64) -> Quarter"
          ],
          "reference": "fune!(dates.quarter@^1);  // then call quarter(…)",
          "url": "http://www.functionalweave.com/functions/dates.quarter"
        },
        {
          "id": "dates.week-number",
          "tier": "optional",
          "why": "ISO week number and week-year, for weekly reports.",
          "section": "reporting-periods",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "ISO 8601 week number and week-numbering year of a date: weeks start Monday, week 1 holds the first Thursday.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "weekNumber"
          ],
          "signatures": [
            "pub fn week_number(iso: &str) -> IsoWeek"
          ],
          "reference": "fune!(dates.week-number@^1);  // then call week_number(…)",
          "url": "http://www.functionalweave.com/functions/dates.week-number"
        },
        {
          "id": "dates.day-count-fraction",
          "tier": "optional",
          "why": "Year fraction by ACT/365F, ACT/360, 30/360 or ACT/ACT, for interest periods.",
          "section": "reporting-periods",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "Year fraction between two dates by ACT/365F, ACT/360, 30/360, 30E/360 or ACT/ACT ISDA, as an exact fraction.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "dayCountFraction"
          ],
          "signatures": [
            "pub fn day_count_fraction(start_iso: &str, end_iso: &str, convention: &str) -> YearFraction"
          ],
          "reference": "fune!(dates.day-count-fraction@^1);  // then call day_count_fraction(…)",
          "url": "http://www.functionalweave.com/functions/dates.day-count-fraction"
        }
      ],
      "gaps": []
    },
    {
      "key": "working-days",
      "title": "Working days and holidays",
      "purpose": "Skip weekends and public holidays when counting or adding days.",
      "from": "dates-basics",
      "members": [
        {
          "id": "dates.bank-holidays",
          "tier": "core",
          "why": "UK bank holidays for a region and year, as gov.uk publishes them.",
          "section": "working-days",
          "from": "dates-basics",
          "version": "1.0.1",
          "summary": "UK bank and public holidays for a region and year, as published by gov.uk, including one-off holidays.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "bankHolidays"
          ],
          "signatures": [
            "pub fn bank_holidays(region: &str, year: i64) -> Vec<BankHoliday>"
          ],
          "reference": "fune!(dates.bank-holidays@^1);  // then call bank_holidays(…)",
          "url": "http://www.functionalweave.com/functions/dates.bank-holidays"
        },
        {
          "id": "dates.add-business-days",
          "tier": "core",
          "why": "Moves a date by working days, skipping weekends and a holiday list.",
          "section": "working-days",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "Move a date forward or back by working days, skipping weekends and a caller-supplied holiday list.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "addBusinessDays"
          ],
          "signatures": [
            "pub fn add_business_days(iso: &str, days: i64, holidays: &[String]) -> String"
          ],
          "reference": "fune!(dates.add-business-days@^1);  // then call add_business_days(…)",
          "url": "http://www.functionalweave.com/functions/dates.add-business-days"
        },
        {
          "id": "dates.business-days-between",
          "tier": "core",
          "why": "Working days between two dates, for SLAs and notice periods.",
          "section": "working-days",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "Working days between two dates, excluding weekends and a caller-supplied holiday list.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "businessDaysBetween"
          ],
          "signatures": [
            "pub fn business_days_between(start_iso: &str, end_iso: &str, holidays: &[String]) -> i64"
          ],
          "reference": "fune!(dates.business-days-between@^1);  // then call business_days_between(…)",
          "url": "http://www.functionalweave.com/functions/dates.business-days-between"
        }
      ],
      "gaps": []
    },
    {
      "key": "repeating-dates",
      "title": "Repeating schedules",
      "purpose": "Generate the dates of something that repeats.",
      "from": "dates-basics",
      "members": [
        {
          "id": "dates.recurrence",
          "tier": "optional",
          "why": "The next n dates of a rule: monthly on the 31st, last Friday, every two weeks.",
          "section": "repeating-dates",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "The next n dates of a repeating rule: monthly on a day, last weekday of the month, every k days or weeks, yearly.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "recurrence"
          ],
          "signatures": [
            "pub fn recurrence(rule: &RecurrenceRule, start_iso: &str, count: i64) -> Vec<String>"
          ],
          "reference": "fune!(dates.recurrence@^1);  // then call recurrence(…)",
          "url": "http://www.functionalweave.com/functions/dates.recurrence"
        }
      ],
      "gaps": []
    },
    {
      "key": "times",
      "title": "Times and durations",
      "purpose": "Work with times of day, durations and timestamps.",
      "from": "dates-basics",
      "members": [
        {
          "id": "time.duration",
          "tier": "optional",
          "why": "Parses and adds durations like 1h30m in whole minutes, and formats the total.",
          "section": "times",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "Parse durations written as 1h30m, 90m or 01:30, add them up in whole minutes, and format the total.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "duration"
          ],
          "signatures": [
            "pub fn duration(parts: &[String]) -> Duration"
          ],
          "reference": "fune!(time.duration@^1);  // then call duration(…)",
          "url": "http://www.functionalweave.com/functions/time.duration"
        },
        {
          "id": "time.minutes-between",
          "tier": "optional",
          "why": "Minutes between two local date-times, across midnight.",
          "section": "times",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "Minutes from one local date and time to another, correct across midnight; wall-clock time, no time zones.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "minutesBetween"
          ],
          "signatures": [
            "pub fn minutes_between(start_date: &str, start_time: &str, end_date: &str, end_time: &str) -> i64"
          ],
          "reference": "fune!(time.minutes-between@^1);  // then call minutes_between(…)",
          "url": "http://www.functionalweave.com/functions/time.minutes-between"
        },
        {
          "id": "time.round-to-increment",
          "tier": "optional",
          "why": "Rounds minutes to a billing increment such as 6 or 15.",
          "section": "times",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "Round a duration in minutes to a billing increment such as 6 or 15 minutes, up, down or to nearest.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "roundToIncrement"
          ],
          "signatures": [
            "pub fn round_to_increment(minutes: i64, increment: i64, mode: &RoundingMode) -> i64"
          ],
          "reference": "fune!(time.round-to-increment@^1);  // then call round_to_increment(…)",
          "url": "http://www.functionalweave.com/functions/time.round-to-increment"
        },
        {
          "id": "time.iso-to-unix",
          "tier": "optional",
          "why": "RFC 3339 timestamps to Unix seconds.",
          "section": "times",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "An RFC 3339 timestamp with a Z or offset, such as 2026-09-26T13:00:00+01:00, to Unix time in whole seconds.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "isoToUnix"
          ],
          "signatures": [
            "pub fn iso_to_unix(timestamp: &str) -> i64"
          ],
          "reference": "fune!(time.iso-to-unix@^1);  // then call iso_to_unix(…)",
          "url": "http://www.functionalweave.com/functions/time.iso-to-unix"
        },
        {
          "id": "time.unix-to-iso",
          "tier": "optional",
          "why": "Unix seconds to an ISO 8601 UTC timestamp.",
          "section": "times",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "Unix time in seconds to an ISO 8601 UTC timestamp such as 2026-09-26T12:00:00Z, for years 0001 to 9999.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "unixToIso"
          ],
          "signatures": [
            "pub fn unix_to_iso(seconds: i64) -> String"
          ],
          "reference": "fune!(time.unix-to-iso@^1);  // then call unix_to_iso(…)",
          "url": "http://www.functionalweave.com/functions/time.unix-to-iso"
        },
        {
          "id": "time.countdown",
          "tier": "optional",
          "why": "Seconds left until a moment and a 4:05 style timer text.",
          "section": "times",
          "from": "dates-basics",
          "version": "1.0.0",
          "summary": "Seconds left until a Unix time, whether it has passed, and a timer text like 4:05, for tokens or retry waits.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "countdown"
          ],
          "signatures": [
            "pub fn countdown(until: i64, now: i64) -> Countdown"
          ],
          "reference": "fune!(time.countdown@^1);  // then call countdown(…)",
          "url": "http://www.functionalweave.com/functions/time.countdown"
        }
      ],
      "gaps": []
    },
    {
      "key": "vat",
      "title": "VAT",
      "purpose": "Work out VAT from the dated rates HMRC publishes.",
      "from": "uk-tax",
      "members": [
        {
          "id": "finance.tax.vat-rate",
          "tier": "core",
          "why": "The VAT rate in force for a jurisdiction, category and date; the others look it up.",
          "section": "vat",
          "from": "uk-tax",
          "version": "1.2.2",
          "summary": "Look up the VAT rate in force for a jurisdiction, category and date.",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "vatRate"
          ],
          "signatures": [
            "pub fn vat_rate(jurisdiction: &str, category: &str, on_date: &str) -> VatRate"
          ],
          "reference": "fune!(finance.tax.vat-rate@^1);  // then call vat_rate(…)",
          "url": "http://www.functionalweave.com/functions/finance.tax.vat-rate"
        },
        {
          "id": "finance.tax.add-vat",
          "tier": "core",
          "why": "Net to gross: VAT on a net amount at the rate on the date of supply.",
          "section": "vat",
          "from": "uk-tax",
          "version": "1.0.1",
          "summary": "Add VAT to a net amount using the rate in force on the date of supply.",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "addVat"
          ],
          "signatures": [
            "pub fn add_vat(net: &Money, jurisdiction: &str, category: &str, on_date: &str) -> VatBreakdown"
          ],
          "reference": "fune!(finance.tax.add-vat@^1);  // then call add_vat(…)",
          "url": "http://www.functionalweave.com/functions/finance.tax.add-vat"
        },
        {
          "id": "finance.tax.remove-vat",
          "tier": "core",
          "why": "Gross to net: the VAT already inside a VAT-inclusive price.",
          "section": "vat",
          "from": "uk-tax",
          "version": "1.0.2",
          "summary": "Extract the VAT already included in a gross amount, using the rate in force on the date of supply.",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "removeVat"
          ],
          "signatures": [
            "pub fn remove_vat(gross: &Money, jurisdiction: &str, category: &str, on_date: &str) -> VatBreakdown"
          ],
          "reference": "fune!(finance.tax.remove-vat@^1);  // then call remove_vat(…)",
          "url": "http://www.functionalweave.com/functions/finance.tax.remove-vat"
        },
        {
          "id": "finance.tax.vat-return",
          "tier": "optional",
          "why": "The nine-box VAT return totals for a period from categorised sales and purchases.",
          "section": "vat",
          "from": "uk-tax",
          "version": "1.0.1",
          "summary": "UK nine-box VAT return totals for a period from categorised sales and purchases (VAT Notice 700/12).",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "vatReturn"
          ],
          "signatures": [
            "pub fn vat_return(transactions: &[VatTransaction], period_start: &str, period_end: &str) -> VatReturn"
          ],
          "reference": "fune!(finance.tax.vat-return@^1);  // then call vat_return(…)",
          "url": "http://www.functionalweave.com/functions/finance.tax.vat-return"
        },
        {
          "id": "finance.tax.vat-flat-rate",
          "tier": "optional",
          "why": "VAT due under the Flat Rate Scheme by business sector, for small businesses on it.",
          "section": "vat",
          "from": "uk-tax",
          "version": "1.0.1",
          "summary": "UK VAT Flat Rate Scheme: VAT due on gross turnover at the sector's dated rate, limited cost rate and first-year 1% off.",
          "status": "unreviewed",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "flatRateVat"
          ],
          "signatures": [
            "pub fn flat_rate_vat(turnover: &Money, sector: &str, limited_cost_business: bool, registration_date: Option<&str>, supply_date: &str) -> FlatRateVat"
          ],
          "reference": "fune!(finance.tax.vat-flat-rate@^1);  // then call flat_rate_vat(…)",
          "url": "http://www.functionalweave.com/functions/finance.tax.vat-flat-rate"
        }
      ],
      "gaps": []
    },
    {
      "key": "tax-year",
      "title": "Tax periods",
      "purpose": "Put dates into the UK periods tax is worked out over.",
      "from": "uk-tax",
      "members": [
        {
          "id": "dates.uk-tax-year",
          "tier": "core",
          "why": "Which UK tax year (6 April to 5 April) a date falls in.",
          "section": "tax-year",
          "from": "uk-tax",
          "version": "1.0.0",
          "summary": "The UK personal tax year containing a date: 6 April to 5 April, with HMRC's label.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "ukTaxYear"
          ],
          "signatures": [
            "pub fn uk_tax_year(iso: &str) -> UkTaxYear"
          ],
          "reference": "fune!(dates.uk-tax-year@^1);  // then call uk_tax_year(…)",
          "url": "http://www.functionalweave.com/functions/dates.uk-tax-year"
        }
      ],
      "gaps": []
    },
    {
      "key": "identifiers",
      "title": "Tax identifiers",
      "purpose": "Check the numbers HMRC and Companies House issue before storing them.",
      "from": "uk-tax",
      "members": [
        {
          "id": "validation.uk-vat-number",
          "tier": "core",
          "why": "Checks a UK VAT registration number's checksum.",
          "section": "identifiers",
          "from": "uk-tax",
          "version": "1.0.0",
          "summary": "Check a UK VAT registration number against HMRC's mod-97 checksum, including the post-2010 9755 variant.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "isUkVatNumber"
          ],
          "signatures": [
            "pub fn is_uk_vat_number(value: &str) -> bool"
          ],
          "reference": "fune!(validation.uk-vat-number@^1);  // then call is_uk_vat_number(…)",
          "url": "http://www.functionalweave.com/functions/validation.uk-vat-number"
        },
        {
          "id": "validation.uk-utr",
          "tier": "optional",
          "why": "Checks a Unique Taxpayer Reference's check digit.",
          "section": "identifiers",
          "from": "uk-tax",
          "version": "2.0.1",
          "summary": "Check an HMRC Unique Taxpayer Reference's modulus 11 check digit, accepting the K and spacing people type.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "validateUkUtr"
          ],
          "signatures": [
            "pub fn validate_uk_utr(value: &str) -> UkUtr"
          ],
          "reference": "fune!(validation.uk-utr@^2);  // then call validate_uk_utr(…)",
          "url": "http://www.functionalweave.com/functions/validation.uk-utr"
        },
        {
          "id": "validation.uk-company-number",
          "tier": "optional",
          "why": "Checks and pads a Companies House company number.",
          "section": "identifiers",
          "from": "uk-tax",
          "version": "2.0.1",
          "summary": "Check a Companies House company number's format and prefix (SC, NI, OC, LP...) and zero-pad it to eight characters.",
          "status": "stable",
          "license": "NOASSERTION",
          "languages": [
            "typescript",
            "python",
            "rust"
          ],
          "available": true,
          "group": false,
          "functions": [
            "validateUkCompanyNumber"
          ],
          "signatures": [
            "pub fn validate_uk_company_number(value: &str) -> UkCompanyNumber"
          ],
          "reference": "fune!(validation.uk-company-number@^2);  // then call validate_uk_company_number(…)",
          "url": "http://www.functionalweave.com/functions/validation.uk-company-number"
        }
      ],
      "gaps": []
    }
  ],
  "gaps": [
    {
      "key": "market-data",
      "text": "Prices, fund data and corporate actions come from a market data provider.",
      "section": "portfolio",
      "from": "investments"
    },
    {
      "key": "order-execution",
      "text": "Placing trades with a broker or custodian (and settlement) is not in caps.",
      "section": "portfolio",
      "from": "investments"
    },
    {
      "key": "cashflow-modelling",
      "text": "Stochastic (Monte Carlo) and lifetime cash-flow modelling are not in caps.",
      "section": "planning",
      "from": "investments"
    },
    {
      "key": "suitability",
      "text": "Suitability and appropriateness assessments (risk profiling) are regulated advice processes caps does not provide.",
      "section": null,
      "from": "investments"
    },
    {
      "key": "income-tax-dividends",
      "text": "Tax on dividends and savings interest outside wrappers is not computed by caps.",
      "section": null,
      "from": "investments"
    },
    {
      "key": "fx-rate-source",
      "text": "Where exchange rates come from: money.convert takes a rate you supply; fetching and storing daily rates (ECB, a provider's API) is yours.",
      "section": null,
      "from": "money-basics"
    },
    {
      "key": "money-storage",
      "text": "Storing amounts: the database columns (integer minor units plus a currency code) and their migrations are yours.",
      "section": null,
      "from": "money-basics"
    },
    {
      "key": "time-zones",
      "text": "Time zones and daylight saving: caps works in ISO dates, UTC and wall-clock times; converting with the IANA tz rules is yours.",
      "section": null,
      "from": "dates-basics"
    },
    {
      "key": "locale-formatting",
      "text": "Showing dates in a user's language and format (\"3 octobre 2026\"): caps returns ISO dates, not localised text.",
      "section": null,
      "from": "dates-basics"
    },
    {
      "key": "non-uk-holidays",
      "text": "Public holidays outside the UK: dates.bank-holidays is UK only; pass another country's list to the working-day functions yourself.",
      "section": null,
      "from": "dates-basics"
    },
    {
      "key": "mtd-submission",
      "text": "Making Tax Digital: submitting the return to HMRC's VAT API (OAuth, fraud-prevention headers, obligations) is yours; caps gives the nine boxes.",
      "section": null,
      "from": "uk-tax"
    },
    {
      "key": "corporation-tax",
      "text": "Corporation tax and self-assessment income tax computations are not in caps.",
      "section": null,
      "from": "uk-tax"
    },
    {
      "key": "vat-number-lookup",
      "text": "Checking that a VAT number is registered (HMRC's lookup API) is network work; caps checks the checksum only.",
      "section": null,
      "from": "uk-tax"
    }
  ],
  "counts": {
    "members": 62,
    "core": 27,
    "optional": 35,
    "unreviewed": 18,
    "deprecated": [],
    "unavailable": [],
    "missing": [],
    "gaps": 13
  },
  "warnings": [
    "8 core capabilities are unreviewed - they pass their tests but await an expert's sign-off; tell the user before relying on them, and never use one silently for tax, payroll, legal, clinical or other regulated rules: invest.time-weighted-return, invest.money-weighted-return, invest.portfolio-weights, invest.rebalance, invest.isa-allowance, finance.tax.vat-rate, finance.tax.add-vat, finance.tax.remove-vat",
    "10 optional capabilities are unreviewed too: invest.cagr, invest.dividend-yield, invest.bond-yield, invest.fee-drag, invest.drawdown-sustainability, invest.capital-gains-tax, invest.section-104-pool, invest.pension-annual-allowance, finance.tax.vat-return, finance.tax.vat-flat-rate",
    "Not financial or tax advice. ISA, pension and capital gains tax rules are UK and dated; regulated advice needs a qualified adviser.",
    "Calculates tax from published rules; it is not tax advice. Have an accountant check how the app uses it before anyone files a return."
  ],
  "url": "http://www.functionalweave.com/suites/investments",
  "owner": null
}