Suites · banking
Banking and payments
Bank accounts and payments: overdraft interest, savings AER, monthly fee caps, Bacs dates, Faster Payments limits, payee checks and cheque wording.
64 capabilities (26 core, 38 optional) and 14 gaps, in build order. Put each line in the file that calls it, then fune build.
UK first: Bacs cycles, Faster Payments and bank holidays follow UK schemes; not financial advice.
TypeScript Python Rust
1. Interest and fees
Charge and pay interest on balances, and cap the fees an account raises.
banking.overdraft-interest core
Overdraft interest for a statement period from daily balances, with an interest-free buffer.
Overdraft interest for a statement period from daily balances, with an interest-free buffer.
fune!(banking.overdraft-interest@^1 ); // then call overdraft_interest(…)
1.0.0
banking.savings-aer core
AER from a nominal rate and how often interest is paid, for savings product pages.
AER (annual equivalent rate) from a gross nominal rate and how often interest is paid, to two decimal places.
fune!(banking.savings-aer@^1 ); // then call savings_aer(…)
1.0.0
banking.fees-cap core
Charges an account's fees in date order up to a monthly cap and waives the rest.
Apply a monthly fee cap to a list of account charges: charge up to the cap, waive the rest.
fune!(banking.fees-cap@^1 ); // then call apply_fee_cap(…)
1.0.0
lending.daily-interest optional Unreviewed
Interest accrued day by day on a changing balance under a day-count convention.
Interest accrued day by day on a changing balance under a day-count convention, summed exactly and rounded once.
fune!(lending.daily-interest@^1 ); // then call daily_interest(…)
1.0.1
finance.compound-interest optional
Compound interest accrued period by period, for savings projections.
Compound interest accrued period by period in minor units, the way a statement is built.
fune!(finance.compound-interest@^1 ); // then call compound_interest(…)
1.0.0
finance.uk-bank-rate optional
Bank of England Bank Rate on a date, for rates that track base.
Bank of England Bank Rate (base rate) in force on a date, from the Bank's official history since 2001.
fune!(finance.uk-bank-rate@^1 ); // then call uk_bank_rate(…)
1.0.1
2. Payments
Send money: check the payee, the scheme limits and when it arrives.
banking.faster-payments-limit core
Whether a Faster Payment fits the scheme maximum, the per-payment limit and what is left of the daily limit.
Whether a Faster Payment fits the scheme maximum, the bank's per-payment limit and what is left of its daily limit.
fune!(banking.faster-payments-limit@^1 ); // then call faster_payments_check(…)
1.0.1
banking.bacs-processing-date core
Bacs input, processing and arrival dates for a submission, skipping weekends and bank holidays.
Bacs three-day cycle: input, processing and entry (arrival) dates for a submission, skipping weekends and bank holidays.
fune!(banking.bacs-processing-date@^1 ); // then call bacs_processing_dates(…)
1.0.0
banking.cheque-amount-words optional
The words and figures to print on a cheque ("One hundred and twenty pounds and fifty pence only").
The words and figures to write on a cheque: "One hundred and twenty pounds and fifty pence only", "£120.50".
fune!(banking.cheque-amount-words@^1 ); // then call cheque_amount_words(…)
1.0.0
text.number-to-words optional
A money amount in words, for cheques and payment confirmations.
Write a money amount in words for a cheque: "one thousand two hundred and thirty-four pounds and fifty-six pence".
fune!(text.number-to-words@^1 ); // then call amount_in_words(…)
1.0.0
payment-rails Actually moving money: Faster Payments, Bacs and SWIFT submissions, or a payments provider's API.confirmation-of-payee Confirmation of Payee name checks: a network service between banks.
3. Statements and transactions
Show customers their transactions and balances.
collections.paginate optional
Pages through transaction lists for statement screens and APIs.
Slice a list into a 1-based page and report the totals an API response needs.
fune!(collections.paginate@^1 ); // then call paginate(…)
1.0.0
collections.group-by-key optional
Groups transactions by day or category for a statement view.
Group records by the value at one key, preserving input order inside each group.
fune!(collections.group-by-key@^1 ); // then call group_by_key(…)
1.0.0
finance.bank-reconcile-match optional
Matches statement lines to expected payments by amount, date window and reference.
Match bank statement lines to ledger entries by exact amount, a date window and reference similarity, deterministically.
fune!(finance.bank-reconcile-match @^1 ); // then call match_bank_lines(…)
1.0.0
text.mask optional
Masks account and card numbers on screens and statements.
Mask all but the last n characters of a card, account or phone number, optionally keeping separators.
fune!(text.mask@^1 ); // then call mask(…)
1.0.0
categorisation Categorising transactions (merchant names to spending categories) is not in caps.
Hold money as currency-tagged integer minor units and do plain arithmetic on it safely.
money.amount core
The Money type ({ minor, currency }) every other money capability takes and returns.
A currency-tagged monetary amount held in integer minor units.
fune!(money.amount@^1 ); // then call money(…)
1.0.2
money.add core
Adds and subtracts amounts, refusing to mix currencies by accident.
Add, subtract and negate monetary amounts, refusing to mix currencies.
fune!(money.add@^1 ); // then call add_money(…)
1.0.1
money.sum core
Totals a list of amounts, with an explicit currency for an empty list.
Total a list of monetary amounts, with an explicit currency for the empty case.
fune!(money.sum@^1 ); // then call sum_money(…)
1.0.1
money.compare core
Compares, mins, maxes and clamps amounts of one currency without unwrapping them.
Compare two amounts of one currency, refusing to compare across currencies; min, max and clamp too.
fune!(money.compare@^2 ); // then call compare_money, min_money, max_money, clamp_money
2.0.04 functions
5. Rates and rounding from money-basics
Apply percentages and divide amounts with the rounding stated, never a float.
money.apply-rate core
Applies a basis-point rate (VAT, discount, commission) to an amount with explicit rounding.
Apply a rate expressed in basis points to a monetary amount, with an explicit rounding mode.
fune!(money.apply-rate@^1 ); // then call apply_rate(…)
1.0.1
math.round-div core
Integer division with a named rounding mode, for any money maths the others do not cover.
Integer division with an explicit rounding mode, for money arithmetic that must not drift.
fune!(math.round-div@^1 ); // then call round_div(…)
1.0.0
math.basis-points optional
Converts "12.5%" to and from basis points exactly, for rates typed in by users.
Convert a rate between percent, basis points and a plain ratio exactly, as decimal text or integer basis points.
fune!(math.basis-points@^2 ); // then call convert_rate, to_basis_points, from_basis_points
2.0.03 functions
math.percent-change optional
Percentage change between two figures in basis points, for "up 4.2% on last month".
Percentage change from one value to another, in basis points, with an explicit rounding mode.
fune!(math.percent-change@^1 ); // then call percent_change(…)
1.0.0
math.rational optional
Exact fractions for rates that must not drift across many steps.
Exact fraction arithmetic, always reduced, for rates and ratios that must not drift.
fune!(math.rational@^2 ); // then call calculate_rational, rational, add_rational, subtract_rational, multiply_rational, divide_rational, compare_rational, rational_to_integer
2.0.08 functions
math.round-div-big optional
Rounded division on numbers past 2^53, for very large totals.
Divide two integers of any size with an explicit rounding mode, on decimal strings, for exact money sums past 2^53.
fune!(math.round-div-big@^1 ); // then call round_div_big(…)
1.0.0
Divide an amount between people, periods or lines so the parts add back to the whole.
money.allocate core
Splits an amount by ratios (60/40, by quantity) without losing or inventing a penny.
Split an amount across ratios without losing or inventing a single minor unit.
fune!(money.allocate@^1 ); // then call allocate(…)
1.0.1
money.split-even optional
Splits an amount into n near-equal parts that sum exactly, for instalments or shares.
Split an amount into n near-equal parts that add back up to exactly the whole.
fune!(money.split-even@^1 ); // then call split_even(…)
1.0.0
7. Display and input from money-basics
Show amounts to people and read what they type.
money.format core
Renders an amount as text with the currency's real number of decimal places.
Render a monetary amount as text, using the currency's real minor-unit precision.
fune!(money.format@^1 ); // then call format_money(…)
1.0.0
money.parse optional
Reads "£1,234.50" or "1.234,50 €" typed by a user into minor units, strictly.
Parse "£1,234.50" or "1.234,50 €" into integer minor units, strictly: no guessing, no rounding.
fune!(money.parse@^1 ); // then call parse_money(…)
1.0.0
money.currency-digits optional
How many decimal places each ISO 4217 currency has, for input boxes and validation.
How many decimal places a currency's minor unit has, from the ISO 4217 list.
fune!(money.currency-digits@^1 ); // then call currency_digits(…)
1.0.0
8. Other currencies from money-basics
Convert between currencies at a rate you hold.
money.convert optional
Converts an amount at a supplied exact rate with explicit rounding.
Convert an amount to another currency at a supplied exact rate, with an explicit rounding mode.
fune!(money.convert@^1 ); // then call convert_money(…)
1.0.0
9. Calendar arithmetic from dates-basics
Move and measure ISO dates exactly, with no date library and no clock reads.
dates.add-days core
Shifts a date by whole days, for due dates and windows.
Shift an ISO date by a whole number of days, forwards or backwards, with exact calendar arithmetic.
fune!(dates.add-days@^1 ); // then call add_days(…)
1.0.0
dates.add-months core
Adds months clamping to month end, so 31 January plus a month is the end of February.
Add calendar months to an ISO date, clamping to the month end: 31 Jan + 1 month is 28 or 29 Feb.
fune!(dates.add-months@^1 ); // then call add_months(…)
1.0.0
dates.days-between core
Signed calendar days between two dates, for ages of invoices and stays.
Calendar days from one ISO date to another, signed: negative when the second date is earlier.
fune!(dates.days-between@^1 ); // then call days_between(…)
1.0.0
dates.month-boundaries core
First and last day of a date's month, for monthly periods and statements.
The first day, last day and length of the calendar month containing a date.
fune!(dates.month-boundaries@^1 ); // then call month_boundaries(…)
1.0.0
dates.day-of-week core
ISO weekday of a date, for weekend rules and opening hours.
The ISO 8601 day of the week for a date: 1 is Monday through 7 is Sunday.
fune!(dates.day-of-week@^1 ); // then call day_of_week(…)
1.0.0
dates.is-leap-year optional
Whether a year is a leap year, for 365/366-day calculations.
Whether a year is a Gregorian leap year: every 4th, except centuries, except every 400th.
fune!(dates.is-leap-year@^1 ); // then call is_leap_year(…)
1.0.0
dates.overlap optional
Days two date ranges share, for prorating and clash checks.
Days two date ranges have in common, with the end of each range stated as inclusive or exclusive.
fune!(dates.overlap@^1 ); // then call overlap_days(…)
1.0.0
dates.age optional
Age in whole years on a date, handling 29 February birthdays.
Age in whole years on a given date, with 29 February birthdays ageing on 1 March in other years.
fune!(dates.age@^1 ); // then call age(…)
1.0.0
10. Periods and reporting dates from dates-basics
Put dates into the periods reports are grouped by.
dates.quarter core
Calendar and fiscal quarter of a date for any year-start month.
Calendar quarter and fiscal quarter of a date, with the fiscal year and quarter date ranges, for any start month.
fune!(dates.quarter@^1 ); // then call quarter(…)
1.0.0
dates.week-number optional
ISO week number and week-year, for weekly reports.
ISO 8601 week number and week-numbering year of a date: weeks start Monday, week 1 holds the first Thursday.
fune!(dates.week-number@^1 ); // then call week_number(…)
1.0.0
dates.day-count-fraction optional
Year fraction by ACT/365F, ACT/360, 30/360 or ACT/ACT, for interest periods.
Year fraction between two dates by ACT/365F, ACT/360, 30/360, 30E/360 or ACT/ACT ISDA, as an exact fraction.
fune!(dates.day-count-fraction@^1 ); // then call day_count_fraction(…)
1.0.0
11. Working days and holidays from dates-basics
Skip weekends and public holidays when counting or adding days.
dates.bank-holidays core
UK bank holidays for a region and year, as gov.uk publishes them.
UK bank and public holidays for a region and year, as published by gov.uk, including one-off holidays.
fune!(dates.bank-holidays@^1 ); // then call bank_holidays(…)
1.0.1
dates.add-business-days core
Moves a date by working days, skipping weekends and a holiday list.
Move a date forward or back by working days, skipping weekends and a caller-supplied holiday list.
fune!(dates.add-business-days@^1 ); // then call add_business_days(…)
1.0.0
dates.business-days-between core
Working days between two dates, for SLAs and notice periods.
Working days between two dates, excluding weekends and a caller-supplied holiday list.
fune!(dates.business-days-between@^1 ); // then call business_days_between(…)
1.0.0
12. Repeating schedules from dates-basics
Generate the dates of something that repeats.
dates.recurrence optional
The next n dates of a rule: monthly on the 31st, last Friday, every two weeks.
The next n dates of a repeating rule: monthly on a day, last weekday of the month, every k days or weeks, yearly.
fune!(dates.recurrence@^1 ); // then call recurrence(…)
1.0.0
13. Times and durations from dates-basics
Work with times of day, durations and timestamps.
time.duration optional
Parses and adds durations like 1h30m in whole minutes, and formats the total.
Parse durations written as 1h30m, 90m or 01:30, add them up in whole minutes, and format the total.
fune!(time.duration@^1 ); // then call duration(…)
1.0.0
time.minutes-between optional
Minutes between two local date-times, across midnight.
Minutes from one local date and time to another, correct across midnight; wall-clock time, no time zones.
fune!(time.minutes-between@^1 ); // then call minutes_between(…)
1.0.0
time.round-to-increment optional
Rounds minutes to a billing increment such as 6 or 15.
Round a duration in minutes to a billing increment such as 6 or 15 minutes, up, down or to nearest.
fune!(time.round-to-increment@^1 ); // then call round_to_increment(…)
1.0.0
time.iso-to-unix optional
RFC 3339 timestamps to Unix seconds.
An RFC 3339 timestamp with a Z or offset, such as 2026-09-26T13:00:00+01:00, to Unix time in whole seconds.
fune!(time.iso-to-unix@^1 ); // then call iso_to_unix(…)
1.0.0
time.unix-to-iso optional
Unix seconds to an ISO 8601 UTC timestamp.
Unix time in seconds to an ISO 8601 UTC timestamp such as 2026-09-26T12:00:00Z, for years 0001 to 9999.
fune!(time.unix-to-iso@^1 ); // then call unix_to_iso(…)
1.0.0
time.countdown optional
Seconds left until a moment and a 4:05 style timer text.
Seconds left until a Unix time, whether it has passed, and a timer text like 4:05, for tokens or retry waits.
fune!(time.countdown@^1 ); // then call countdown(…)
1.0.0
Check payee and customer bank details before money moves.
validation.iban core
Checks an IBAN's mod-97 checksum and its country's length.
Check an IBAN against the ISO 13616 mod-97-10 checksum and the registered length for its country.
fune!(validation.iban@^1 ); // then call is_iban(…)
1.0.0
validation.bic optional
Checks a SWIFT/BIC code's format and splits it.
Check the format of a SWIFT/BIC code (8 or 11 characters) and split it into its parts.
fune!(validation.bic@^1 ); // then call validate_bic(…)
1.0.0
validation.uk-sort-code-account optional
Checks a UK sort code and account number by the Vocalink modulus rules, against a table you supply.
Check a UK sort code and account number with the Vocalink/Pay.UK modulus rules, against a table you supply.
fune!(validation.uk-sort-code-account@^3 ); // then call validate_uk_sort_code_account(…)
3.0.0
validation.uk-modulus-table optional
Parses Vocalink's VALACDOS and SCSUBTAB files into that table.
Parse Vocalink's VALACDOS.txt and SCSUBTAB.txt into the table UK sort code modulus checking needs.
fune!(validation.uk-modulus-table@^1 ); // then call parse_uk_modulus_table(…)
1.0.0
16. Identifiers and check digits from validation-basics
Catch mistyped reference numbers by their check digits.
validation.luhn optional
Luhn mod-10 check, for card numbers and many reference numbers.
Check a digit string against the Luhn mod-10 checksum used by payment cards and many identifiers.
fune!(validation.luhn@^1 ); // then call is_luhn(…)
1.0.0
validation.uk-company-number optional
Checks a Companies House number's format and prefix.
Check a Companies House company number's format and prefix (SC, NI, OC, LP...) and zero-pad it to eight characters.
fune!(validation.uk-company-number@^2 ); // then call validate_uk_company_number(…)
2.0.1
validation.lei optional
Checks a Legal Entity Identifier's check digits.
Check a 20-character Legal Entity Identifier against its ISO 17442 / ISO 7064 MOD 97-10 check digits.
fune!(validation.lei@^1 ); // then call validate_lei(…)
1.0.0
validation.gtin optional
Checks an EAN/UPC/GTIN barcode number.
Check an EAN-8, UPC-A, EAN-13 or GTIN-14 barcode number against the GS1 mod-10 check digit.
fune!(validation.gtin@^1 ); // then call validate_gtin(…)
1.1.0
Gaps What this kind of app usually needs that Functional Weave does not have yet: write these yourself, or use a service.
kyc-aml Know-your-customer checks, sanctions screening and anti-money-laundering monitoring are services and policy caps does not have.ledger-of-record A core banking ledger (accounts, holds, postings, idempotent transfers) to keep balances is yours; caps works out the figures.card-issuing Card issuing, authorisations and chargebacks go through a card processor.fx-rate-source Where exchange rates come from: money.convert takes a rate you supply; fetching and storing daily rates (ECB, a provider's API) is yours.money-storage Storing amounts: the database columns (integer minor units plus a currency code) and their migrations are yours.time-zones Time zones and daylight saving: caps works in ISO dates, UTC and wall-clock times; converting with the IANA tz rules is yours.locale-formatting Showing dates in a user's language and format ("3 octobre 2026"): caps returns ISO dates, not localised text.non-uk-holidays Public holidays outside the UK: dates.bank-holidays is UK only; pass another country's list to the working-day functions yourself.address-lookup Turning a postcode into a list of addresses (Royal Mail PAF or a lookup API) is network work and not in caps.email-deliverability Whether a mailbox exists (MX lookups, a confirmation email): validation.email checks the syntax only.vocalink-data The Vocalink modulus tables themselves: download them from Pay.UK under its terms; caps parses them but does not ship them.