§

L4 Core Libraries

L4 ships with a set of core libraries that provide essential functions for common tasks. These libraries are written in L4 itself and serve as both utilities and examples of idiomatic L4 code.

Overview

Core libraries are located in the jl4-core/libraries/ directory:

  • prelude - Standard functions (automatically imported)
  • daydate - Date calculations and temporal logic
  • time - Wall-clock time-of-day operations
  • datetime - Absolute points in time with timezones
  • timezone - IANA timezone constants
  • excel-date - Excel date compatibility
  • math - Mathematical functions
  • currency - Currency handling (ISO 4217)
  • legal-persons - Legal entity types and capacity
  • jurisdiction - Jurisdiction definitions
  • holdings - Holdings and ownership
  • actus - ACTUS financial contract types and evaluation
  • date-compat - Legacy DATE syntax compatibility
  • llm - LLM API integration

Using Libraries

Libraries require explicit import:

IMPORT daydate
IMPORT math
IMPORT currency

Import Paths

Import by library name or file path:

IMPORT daydate                   -- Standard/core library
IMPORT "my-custom-lib.l4"        -- Custom library

Library Quick Reference

Condensed function tables for each core library. See individual library pages for full details.

prelude

Automatically imported. Provides foundational functions for lists, numbers, and data types.

List Functions:

Function Type Description
null list [a] → Bool Is list empty?
count list [a] → Number List length
map f list (a→b) → [a] → [b] Transform each element
filter f list (a→Bool) → [a] → [a] Keep matching elements
foldr f z list (a→r→r) → r → [a] → r Right fold
foldl f z list (r→a→r) → r → [a] → r Left fold
append l1 l2 [a] → [a] → [a] Concatenate lists
concat lists [[a]] → [a] Flatten list of lists
reverse list [a] → [a] Reverse list
at list i [a] → Number → a Index access (0-based)
take n list Number → [a] → [a] First n elements
drop n list Number → [a] → [a] Drop first n elements
elem x list a → [a] → Bool Membership test
sort list [Number] → [Number] Sort ascending
zip l1 l2 [a] → [b] → [Pair a b] Pair up elements
nub list [a] → [a] Remove duplicates
partition f list (a→Bool) → [a] → Pair [a] [a] Split by predicate

Boolean Quantifiers:

Function Type Description
all f list (a→Bool) → [a] → Bool All satisfy predicate?
any f list (a→Bool) → [a] → Bool Any satisfy predicate?
and list [Bool] → Bool All true?
or list [Bool] → Bool Any true?

Numeric:

Function Type Description
sum list [Number] → Number Sum of numbers
product list [Number] → Number Product of numbers
max x y Number → Number → Number Maximum of two
min x y Number → Number → Number Minimum of two
maximum list [Number] → Number Maximum of list
minimum list [Number] → Number Minimum of list

Maybe (Optional):

Function Type Description
fromMaybe default x a → Maybe a → a Unwrap with default
isJust x Maybe a → Bool Is Just?
isNothing x Maybe a → Bool Is Nothing?
mapMaybe f list (a → Maybe b) → [a] → [b] Filter-map
catMaybes list [Maybe a] → [a] Collect Justs

Either, Pair, Utility:

Function Type Description
either left right x (a→c) → (b→c) → Either a b → c Fold over Either
PAIR OF x, y constructor Create pair
p's fst Pair a b → a First element
p's snd Pair a b → b Second element
id x a → a Identity function
const x y a → b → a Always return first

Dictionary:

Function Type Description
emptyDict Dictionary k v Empty dictionary
listToDict pairs [Pair k v] → Dictionary k v Create from pairs
dictLookup key dict k → Dictionary k v → Maybe v Query by key
dictInsert key val dict k → v → Dictionary k v → Dictionary k v Add/replace entry
dictDelete key dict k → Dictionary k v → Dictionary k v Remove entry
dictKeys dict Dictionary k v → [k] All keys
dictElems dict Dictionary k v → [v] All values
mapDict f dict (v→w) → Dict k v → Dict k w Map over values
filterDict f dict (v→Bool) → Dict → Dict Filter by value

See prelude.md for the complete function list including sortBy, zipWith, deleteBy, dictUnion, and more.

math

Requires: IMPORT prelude

Function Type Description
EULER NUMBER Euler's number (2.718...)
exp x NUMBER → NUMBER e^x
ln x NUMBER → MAYBE NUMBER Natural logarithm
log10 x NUMBER → MAYBE NUMBER Base-10 logarithm
sqrt x NUMBER → MAYBE NUMBER Square root
sin x NUMBER → MAYBE NUMBER Sine
cos x NUMBER → MAYBE NUMBER Cosine
tan x NUMBER → MAYBE NUMBER Tangent
asin x NUMBER → MAYBE NUMBER Arcsine (domain [-1,1])
acos x NUMBER → MAYBE NUMBER Arccosine (domain [-1,1])
atan x NUMBER → MAYBE NUMBER Arctangent
absNumber x NUMBER → NUMBER Absolute value

Trig functions return MAYBE to handle domain errors safely.

daydate

Date arithmetic library. ISO 8601 conventions.

Constants: Monday(1) through Sunday(0), January(1) through December(12), Days in a week(7), Days in a year(365.2425), Days in a month(30.44)

Constructors:

Function Type Description
Date day month year NUMBER → NUMBER → NUMBER → DATE From d/m/y
Date days NUMBER → DATE From serial (days since epoch)
Year year NUMBER → DATE Jan 1 of year
Month month year NUMBER → NUMBER → DATE 1st of month
Week week year NUMBER → NUMBER → DATE Monday of ISO week

Queries:

Function Description
Weekday of date Day of week (0=Sun, 1=Mon...)
Week of the year date ISO week number
Month of the year date Month number
is weekend date Saturday or Sunday?
is weekday date Monday through Friday?
is leap year year Leap year?

Relative Dates: the day after date, the day before date, the week after date, the month after date, the year after date, the earlier of date1 date2, the later of date1 date2

Arithmetic: date + n (add days), date - n (subtract days), date1 - date2 (difference in days), date1 >= date2 (comparison)

See daydate.md for full documentation.

time

Wall-clock time of day (no date, no timezone). 24-hour format.

Constants: Midnight (00:00:00), Noon (12:00:00)

Constructors:

Function Description
Time h m s From hours, minutes, seconds
Time h m From hours, minutes (s=0)
Time h m s am/pm 12-hour format with meridiem

Extractors: the hour of t, the minute of t, the second of t

Arithmetic: t `plus hours` n, t `plus minutes` n, t `plus seconds` n, t `minus hours` n, t `minus minutes` n, t `minus seconds` n

Predicates: t `is before noon`, t `is after noon`, t `is morning`, t `is afternoon`, t `is evening`

Comparators: the earlier of t1 t2, the later of t1 t2, t1 >= t2, t1 - t2 (difference in seconds)

See time.md for full documentation.

datetime

Combined date + time + timezone. Stored internally as UTC.

Constructors:

Function Description
Datetime date time Using document TIMEZONE
Datetime date time tz Explicit IANA timezone
Datetime date h m s From date + h/m/s
Datetime date Midnight in document TIMEZONE

Extractors: Date of dt, Time of dt, Timezone of dt, the hour of dt, the minute of dt, the second of dt, the day of dt, the month of dt, the year of dt

Relative: at midnight dt, at noon dt, dt `at` time

Comparators: the earlier of dt1 dt2, the later of dt1 dt2, dt1 >= dt2, dt1 <= dt2

See datetime.md for full documentation.

currency

ISO 4217 currency handling. Uses integer minor units (cents) to avoid floating-point issues. Key functions: Money minorUnits code, major to minor units, add money, multiply money. Supports USD, EUR, GBP, JPY, SGD, and others.

Status: Prototype. API may change. See currency.md.

Legal entity types, identity documents, and capacity checks. Key functions: age in years, is adult birthDate jurisdictionCode, can enter contract, is beneficial owner. Includes corporate entity types and jurisdiction-aware majority age.

Status: Prototype. API may change. See legal-persons.md.

See Also