Module 1: Your First Legal Rule

In this module, you'll write your first legal rule in L4—a simple legal obligation with conditions, deadlines, and consequences.

Learning Objectives

By the end of this module, you will be able to:

• Write a basic legal obligation using PARTY and MUST
• Add conditions using IF
• Set deadlines using WITHIN
• Define consequences using HENCE and LEST
• Test your rule using #EVAL

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A Simple Legal Obligation

Let's start with something every lawyer understands: a simple legal obligation. Find the complete working example later in this document.

The annual return obligation: "A registered charity must file an annual return."

In L4, we write this as:

GIVEN charity IS A RegisteredCharity
`The annual return obligation` MEANS
    PARTY charity
    MUST `file annual return`

Let's break this down:

Code	Meaning
GIVEN charity IS A RegisteredCharity	This rule applies to registered charities
`The annual return obligation` MEANS	The name of this rule
PARTY charity	The charity is the one with the obligation
MUST	This creates a legal obligation
`file annual return`	This is what they must do

Backtick Names

Notice the backticks around file annual return. In L4, backticks let you use spaces and special characters in names. These are called quoted identifiers.

-- These are equivalent ways to name things:
fileReturn          -- camelCase (no spaces)
`file return`       -- quoted identifier (with spaces)
`file annual return`  -- more descriptive

Use backticks when you want names that read like natural language.

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Try It Yourself

Write a rule that says "A solicitor must maintain client confidentiality."

Hint: You'll need to:

1. Define a DECLARE for the Solicitor type
2. Define DECLARE for the Actor and Action types
3. Use PARTY ... MUST ... to create the obligation

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Adding Conditions

Real legal rules have conditions. Let's add one:

IF charity's status EQUALS Active
    PARTY charity
    MUST `file annual return`

The IF keyword adds a condition that must be true for the obligation to apply.

Multiple Conditions

Use AND and OR for multiple conditions:

IF charity's status EQUALS Active
   AND charity's income > 10000

Accessing Fields

The 's syntax accesses fields of a record:

charity's status      -- the status field of charity
charity's income      -- the income field of charity

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Setting Deadlines

Legal obligations usually have deadlines. Use WITHIN:

PARTY charity
MUST `file annual return`
WITHIN 60

WITHIN 60 means "within 60 days." L4 uses days as the default time unit.

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Consequences: HENCE and LEST

What happens when someone complies or doesn't comply? Use HENCE and LEST:

PARTY charity
MUST `file annual return`
WITHIN 60
HENCE FULFILLED
LEST BREACH

Keyword	Meaning
HENCE	What happens if they comply
LEST	What happens if they don't comply

Chaining Obligations

HENCE can trigger another obligation:

PARTY seller
MUST `deliver goods`
WITHIN 14
HENCE
    PARTY buyer
    MUST `pay invoice`
    WITHIN 30
    HENCE FULFILLED
    LEST BREACH
LEST BREACH

This creates a chain: if the seller delivers, the buyer must pay.

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Complete Example

-- Module 1: Your First Legal Rule - Complete Examples
-- All examples are validated and use natural language identifiers

-- =============================================================================
-- SECTION 1: Basic Obligation (simplified for teaching)
-- =============================================================================

-- Define types needed for obligations
DECLARE `Charity Status` IS ONE OF
    Active
    Suspended
    Dissolved

DECLARE `Registered Charity`
    HAS `the name` IS A STRING
        `the status` IS A `Charity Status`
        `the annual income` IS A NUMBER

-- Define actors and actions
DECLARE Party IS ONE OF
    `the charity`
    `the buyer`
    `the seller`
    `the Commissioner`

DECLARE Action IS ONE OF
    `file the annual return`
    `deliver the goods`
    `pay the invoice` HAS amount IS A NUMBER
    `cancel the order`
    `issue a Required Steps Notice`

-- =============================================================================
-- SECTION 2: The Annual Return Obligation
-- =============================================================================

-- A charity's obligation to file an annual return
GIVEN charity IS A `Registered Charity`
GIVETH A DEONTIC Party Action
`the annual return obligation` MEANS
    IF charity's `the status` EQUALS Active
    THEN PARTY `the charity`
         MUST `file the annual return`
         WITHIN 60
         HENCE FULFILLED
         LEST PARTY `the Commissioner`
              MAY `issue a Required Steps Notice`
              HENCE FULFILLED
    ELSE FULFILLED

-- =============================================================================
-- SECTION 3: Chained Obligations - Sale Contract
-- =============================================================================

-- The seller must deliver, then the buyer must pay
GIVETH A DEONTIC Party Action
`the sale contract` MEANS
    PARTY `the seller`
    MUST `deliver the goods`
    WITHIN 14
    HENCE
        PARTY `the buyer`
        MUST `pay the invoice` 1000
        WITHIN 30
        HENCE FULFILLED
        LEST BREACH
    LEST
        PARTY `the seller`
        MAY `cancel the order`
        HENCE FULFILLED

-- =============================================================================
-- SECTION 4: Test Data
-- =============================================================================

`Animal Welfare Society` MEANS `Registered Charity` "Animal Welfare Society" Active 50000

-- =============================================================================
-- SECTION 5: Tests
-- =============================================================================

-- Test field access
#EVAL `Animal Welfare Society`'s `the name`
#EVAL `Animal Welfare Society`'s `the status` EQUALS Active
#EVAL `Animal Welfare Society`'s `the annual income` > 10000

-- Test obligation - charity files on time
#TRACE `the annual return obligation` `Animal Welfare Society` AT 0 WITH
    PARTY `the charity` DOES `file the annual return` AT 30

-- Test sale contract - happy path
#TRACE `the sale contract` AT 0 WITH
    PARTY `the seller` DOES `deliver the goods` AT 10
    PARTY `the buyer` DOES `pay the invoice` 1000 AT 25

Included are:

• Type definitions for charities, actors, and actions
• The annual return obligation with conditions and deadlines
• A chained sale contract
• Test data and #TRACE simulations

Understanding GIVETH A DEONTIC

When a function returns an obligation (not just a value), we use GIVETH A DEONTIC:

• GIVETH A BOOLEAN - returns true/false
• GIVETH A NUMBER - returns a number
• GIVETH A DEONTIC Actor Action - returns an obligation (specifying actor and action types)

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Testing with #EVAL

Use #EVAL to test expressions:

#EVAL testCharity's name
-- Result: "Animal Welfare Society"

#EVAL testCharity's status EQUALS Active
-- Result: TRUE

In VS Code with the L4 extension, hover over #EVAL to see the result.

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Testing with #TRACE

For regulative rules (obligations), use #TRACE to simulate scenarios:

#TRACE `annual return obligation` testCharity AT 0 WITH
    PARTY testCharity DOES `file annual return` AT 30

This simulates:

• Starting at day 0
• The charity filing their return at day 30

The result shows whether the obligation was FULFILLED or BREACH.

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Common Mistakes

1. Missing Type Declaration

-- ❌ Wrong: Type not declared
GIVEN charity IS A RegisteredCharity

-- ✅ Right: Declare the type first
DECLARE RegisteredCharity
    HAS name IS A STRING

2. Wrong Field Access

-- ❌ Wrong: Missing 's
IF charity status EQUALS Active

-- ✅ Right: Use 's for field access
IF charity's status EQUALS Active

3. Missing Backticks for Multi-Word Names

-- ❌ Wrong: Spaces without backticks
MUST file annual return

-- ✅ Right: Use backticks
MUST `file annual return`

Exercises

Exercise 1: Simple Obligation

Write an L4 rule for: "An employee must submit a timesheet every week."

Exercise 2: Conditional Obligation

Write an L4 rule for: "If a tenant is more than 14 days late on rent, the landlord may issue an eviction notice."

Exercise 3: Chained Obligations

Write L4 rules for: "The seller must deliver goods within 14 days. If delivered, the buyer must pay within 30 days."

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Summary

In this module, you learned:

Concept	Syntax
Declare parameters	GIVEN name IS A Type
Create obligation	PARTY actor MUST action
Add condition	IF condition
Set deadline	WITHIN days
Compliance result	HENCE consequence
Non-compliance result	LEST consequence
Test expression	#EVAL expression
Simulate scenario	#TRACE rule AT time WITH events

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What's Next?

In Module 2: Legal Entities, you'll learn how to model complex legal entities with proper types, including records, enums, and relationships between entities.