Module 7: Putting It Together

Prerequisites: Modules 1–6

In this capstone module, you'll build a complete legal model combining everything you've learned.

Learning Objectives

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

• Design a complete L4 model from requirements
• Organize code with sections
• Apply best practices
• Debug common issues
• Know where to go next

---

Capstone Project: Charity Registration

We'll build a simplified charity registration system based on real legislation. This combines:

• Type definitions
• Eligibility rules
• Classification and fee calculations
• Regulative obligations and prohibitions
• Testing

The complete working implementation:

-- Module 7: Putting It Together - Capstone Example
-- A complete charity registration system
-- All examples are validated and use natural language identifiers

IMPORT prelude

-- =============================================================================
-- SECTION 1: Type Definitions
-- =============================================================================

-- Charitable purposes (from legislation)
DECLARE Purpose IS ONE OF
    `prevention or relief of poverty`
    `advancement of education`
    `advancement of religion`
    `advancement of health`
    `advancement of animal welfare`
    `other purpose` HAS `the description` IS A STRING

-- Legal status of a charity
DECLARE Status IS ONE OF
    Active
    Suspended HAS `the reason` IS A STRING
    Deregistered

-- Criminal conviction record
DECLARE Conviction
    HAS `the description` IS A STRING
        `the conviction is spent` IS A BOOLEAN

-- Governor of a charity
DECLARE Governor
    HAS `the governor's name` IS A STRING
        `the governor's age` IS A NUMBER
        `the governor is bankrupt` IS A BOOLEAN
        `the governor's convictions` IS A LIST OF Conviction

-- The main charity record
DECLARE `Registered Charity`
    HAS `the charity's name` IS A STRING
        `the registration number` IS A STRING
        `the charity's status` IS A Status
        `the charity's purposes` IS A LIST OF Purpose
        `the charity's governors` IS A LIST OF Governor

-- =============================================================================
-- SECTION 2: Eligibility Rules
-- =============================================================================

-- A governor must be an adult (at least 18)
GIVEN governor IS A Governor
GIVETH A BOOLEAN
DECIDE `the governor is an adult` IF
    governor's `the governor's age` >= 18

-- Check for disqualifying convictions (unspent convictions)
GIVEN governor IS A Governor
GIVETH A BOOLEAN
DECIDE `the governor has a disqualifying conviction` IF
    any (GIVEN c YIELD c's `the conviction is spent` EQUALS FALSE) (governor's `the governor's convictions`)

-- A person can be a governor if they meet all criteria
GIVEN governor IS A Governor
GIVETH A BOOLEAN
DECIDE `the person can be a governor` IF
    `the governor is an adult` governor
    AND NOT governor's `the governor is bankrupt`
    AND NOT `the governor has a disqualifying conviction` governor

-- A purpose is charitable if it's from the approved list
GIVEN purpose IS A Purpose
GIVETH A BOOLEAN
DECIDE `the purpose is charitable` IS
    CONSIDER purpose
    WHEN `prevention or relief of poverty` THEN TRUE
    WHEN `advancement of education` THEN TRUE
    WHEN `advancement of religion` THEN TRUE
    WHEN `advancement of health` THEN TRUE
    WHEN `advancement of animal welfare` THEN TRUE
    WHEN `other purpose` description THEN FALSE

-- A charity is valid if it has valid purposes and valid governors
GIVEN charity IS A `Registered Charity`
GIVETH A BOOLEAN
DECIDE `the charity is valid` IF
    charity's `the charity's status` EQUALS Active
    AND NOT null (charity's `the charity's purposes`)
    AND all (GIVEN p YIELD `the purpose is charitable` p) (charity's `the charity's purposes`)
    AND NOT null (charity's `the charity's governors`)
    AND all (GIVEN g YIELD `the person can be a governor` g) (charity's `the charity's governors`)

-- =============================================================================
-- SECTION 3: Classification and Fees
-- =============================================================================

-- Classify a charity by its annual income (multi-way decision with BRANCH)
GIVEN `the annual income` IS A NUMBER
GIVETH A STRING
DECIDE `the charity's size band` IS
    BRANCH
        IF `the annual income` < 10000 THEN "small"
        IF `the annual income` < 500000 THEN "medium"
        OTHERWISE "large"

-- The annual filing fee, decomposed with WHERE
GIVEN charity IS A `Registered Charity`
      `the annual income` IS A NUMBER
GIVETH A NUMBER
`the annual filing fee` MEANS
    `the base fee` + `the governor levy`
    WHERE
        `the base fee` MEANS
            BRANCH
                IF `the charity's size band` `the annual income` EQUALS "small" THEN 50
                IF `the charity's size band` `the annual income` EQUALS "medium" THEN 200
                OTHERWISE 500

        `the governor levy` MEANS
            10 * count (charity's `the charity's governors`)

-- =============================================================================
-- SECTION 4: Filing Obligations
-- =============================================================================

-- Actors and actions for the regulatory system
DECLARE Actor IS ONE OF
    `the Charity`
    `the Commissioner`

DECLARE Action IS ONE OF
    `file the annual return`
    `issue a Required Steps Notice`
    `correct the deficiencies`
    `distribute profits to the governors`

-- Annual return filing obligation
GIVEN charity IS A `Registered Charity`
GIVETH A DEONTIC Actor Action
`the annual return obligation` MEANS
    IF charity's `the charity's status` EQUALS Active
    THEN
        PARTY `the Charity`
        MUST `file the annual return`
        WITHIN 60
        HENCE FULFILLED
        LEST
            PARTY `the Commissioner`
            MUST `issue a Required Steps Notice`
            WITHIN 14
            HENCE `the correction period`
            LEST BREACH BY `the Commissioner` BECAUSE "failed to issue notice"
    ELSE FULFILLED

-- After notice is issued, charity has time to correct
GIVETH A DEONTIC Actor Action
`the correction period` MEANS
    PARTY `the Charity`
    MUST `correct the deficiencies`
    WITHIN 30
    HENCE FULFILLED
    LEST BREACH BY `the Charity` BECAUSE "failed to correct after notice"

-- A prohibition: charities must not distribute profits to their governors
GIVETH A DEONTIC Actor Action
`the profit distribution prohibition` MEANS
    PARTY `the Charity`
    SHANT `distribute profits to the governors`
    HENCE FULFILLED
    LEST BREACH BY `the Charity` BECAUSE "distributed profits to governors"

-- =============================================================================
-- SECTION 5: Test Data
-- =============================================================================

-- Valid governor
`Jane Smith` MEANS Governor "Jane Smith" 45 FALSE (LIST)

-- Governor with issues
`John Doe (bankrupt)` MEANS Governor "John Doe" 50 TRUE (LIST)

`unspent conviction` MEANS Conviction "Fraud conviction 2020" FALSE
`Bob Jones (with conviction)` MEANS Governor "Bob Jones" 40 FALSE (LIST `unspent conviction`)

`Young Person` MEANS Governor "Young Person" 16 FALSE (LIST)

-- Valid charity
`Jersey Animal Welfare` MEANS `Registered Charity` "Jersey Animal Welfare" "CH001" Active (LIST `advancement of animal welfare`, `advancement of education`) (LIST `Jane Smith`)

-- Charity with invalid governor
`Problem Charity` MEANS `Registered Charity` "Problem Charity" "CH002" Active (LIST `advancement of education`) (LIST `John Doe (bankrupt)`)

-- Suspended charity
`Suspended Charity` MEANS `Registered Charity` "Suspended Charity" "CH003" (Suspended "Financial irregularities") (LIST `advancement of health`) (LIST `Jane Smith`)

-- =============================================================================
-- SECTION 6: Tests
-- =============================================================================

-- Governor eligibility tests
#EVAL `the governor is an adult` `Jane Smith`
#EVAL `the governor is an adult` `Young Person`
#EVAL `the person can be a governor` `Jane Smith`
#EVAL `the person can be a governor` `John Doe (bankrupt)`
#EVAL `the person can be a governor` `Bob Jones (with conviction)`
#EVAL `the person can be a governor` `Young Person`

-- Charity validity tests
#EVAL `the charity is valid` `Jersey Animal Welfare`
#EVAL `the charity is valid` `Problem Charity`
#EVAL `the charity is valid` `Suspended Charity`

-- Classification and fee tests
#EVAL `the charity's size band` 5000
#EVAL `the charity's size band` 60000
#EVAL `the charity's size band` 750000
#EVAL `the annual filing fee` `Jersey Animal Welfare` 60000

-- Test filing obligation scenarios

-- Happy path: charity files on time
#TRACE `the annual return obligation` `Jersey Animal Welfare` AT 0 WITH
    PARTY `the Charity` DOES `file the annual return` AT 30

-- Suspended charity: no filing required
#TRACE `the annual return obligation` `Suspended Charity` AT 0 WITH

-- Late filing: the charity misses the 60-day deadline (its day-65 filing
-- arrives too late), the Commissioner issues a notice, then the charity
-- corrects within the correction period
#TRACE `the annual return obligation` `Jersey Animal Welfare` AT 0 WITH
    PARTY `the Charity` DOES `file the annual return` AT 65
    PARTY `the Commissioner` DOES `issue a Required Steps Notice` AT 70
    PARTY `the Charity` DOES `correct the deficiencies` AT 90

-- Prohibition: distributing profits is a breach
#TRACE `the profit distribution prohibition` AT 0 WITH
    PARTY `the Charity` DOES `distribute profits to the governors` AT 10

Requirements

1. Charities have names, registration numbers, statuses, purposes, and governors
2. Purposes must be from an approved list
3. Governors must be adults without disqualifying convictions
4. Charities are classified by income into size bands, which determine the filing fee
5. Registered charities must file annual returns within 60 days of year-end
6. Late filing triggers a Required Steps Notice
7. Charities must not distribute profits to their governors

---

Step 1: Define Types

Start by modeling the domain:

-- Charitable purposes (from legislation)
DECLARE Purpose IS ONE OF
    `prevention or relief of poverty`
    `advancement of education`
    `advancement of religion`
    `advancement of health`
    `advancement of animal welfare`
    `other purpose` HAS `the description` IS A STRING

-- Legal status of a charity
DECLARE Status IS ONE OF
    Active
    Suspended HAS `the reason` IS A STRING
    Deregistered

-- Criminal conviction record
DECLARE Conviction
    HAS `the description` IS A STRING
        `the conviction is spent` IS A BOOLEAN

-- Governor of a charity
DECLARE Governor
    HAS `the governor's name` IS A STRING
        `the governor's age` IS A NUMBER
        `the governor is bankrupt` IS A BOOLEAN
        `the governor's convictions` IS A LIST OF Conviction

-- The main charity record
DECLARE `Registered Charity`
    HAS `the charity's name` IS A STRING
        `the registration number` IS A STRING
        `the charity's status` IS A Status
        `the charity's purposes` IS A LIST OF Purpose
        `the charity's governors` IS A LIST OF Governor

Key design decisions:

1. Use natural language field names: `the governor's name` reads like legal text
2. Use enumerations for fixed categories: Prevents typos and invalid values
3. Use lists for multiple items: governors, purposes, convictions

---

Step 2: Define Eligibility Rules

Rules for who can be a governor and what makes a valid charity:

-- A governor must be an adult (at least 18)
GIVEN governor IS A Governor
GIVETH A BOOLEAN
DECIDE `the governor is an adult` IF
    governor's `the governor's age` >= 18

-- Check for disqualifying convictions (unspent convictions)
GIVEN governor IS A Governor
GIVETH A BOOLEAN
DECIDE `the governor has a disqualifying conviction` IF
    any (GIVEN c YIELD c's `the conviction is spent` EQUALS FALSE) (governor's `the governor's convictions`)

-- A person can be a governor if they meet all criteria
GIVEN governor IS A Governor
GIVETH A BOOLEAN
DECIDE `the person can be a governor` IF
    `the governor is an adult` governor
    AND NOT governor's `the governor is bankrupt`
    AND NOT `the governor has a disqualifying conviction` governor

-- A charity is valid if it has valid purposes and valid governors
GIVEN charity IS A `Registered Charity`
GIVETH A BOOLEAN
DECIDE `the charity is valid` IF
    charity's `the charity's status` EQUALS Active
    AND NOT null (charity's `the charity's purposes`)
    AND all (GIVEN p YIELD `the purpose is charitable` p) (charity's `the charity's purposes`)
    AND NOT null (charity's `the charity's governors`)
    AND all (GIVEN g YIELD `the person can be a governor` g) (charity's `the charity's governors`)

Key patterns:

1. Simple predicates: `the governor is an adult`
2. Using any and all with predicates: checking convictions, purposes, and governors
3. Combining conditions: using AND and NOT

Note: These functions require IMPORT prelude for any, all, null, etc.

---

Step 3: Classification and Fees

Constitutive rules from Module 4 in action—a multi-way classification with BRANCH, and a calculation decomposed with WHERE:

-- Classify a charity by its annual income (multi-way decision with BRANCH)
GIVEN `the annual income` IS A NUMBER
GIVETH A STRING
DECIDE `the charity's size band` IS
    BRANCH
        IF `the annual income` < 10000 THEN "small"
        IF `the annual income` < 500000 THEN "medium"
        OTHERWISE "large"

-- The annual filing fee, decomposed with WHERE
GIVEN charity IS A `Registered Charity`
      `the annual income` IS A NUMBER
GIVETH A NUMBER
`the annual filing fee` MEANS
    `the base fee` + `the governor levy`
    WHERE
        `the base fee` MEANS
            BRANCH
                IF `the charity's size band` `the annual income` EQUALS "small" THEN 50
                IF `the charity's size band` `the annual income` EQUALS "medium" THEN 200
                OTHERWISE 500

        `the governor levy` MEANS
            10 * count (charity's `the charity's governors`)

Key patterns:

1. BRANCH for classification: conditions checked top-to-bottom, first match wins
2. WHERE names each part of the formula: the fee is transparently base fee + governor levy
3. Reusing decisions: the fee calculation calls the size-band classification
4. count from the prelude: the number of items in a list

---

Step 4: Define Regulative Rules

The filing obligations and a prohibition:

-- Actors and actions for the regulatory system
DECLARE Actor IS ONE OF
    `the Charity`
    `the Commissioner`

DECLARE Action IS ONE OF
    `file the annual return`
    `issue a Required Steps Notice`
    `correct the deficiencies`
    `distribute profits to the governors`

-- Annual return filing obligation
GIVEN charity IS A `Registered Charity`
GIVETH A DEONTIC Actor Action
`the annual return obligation` MEANS
    IF charity's `the charity's status` EQUALS Active
    THEN
        PARTY `the Charity`
        MUST `file the annual return`
        WITHIN 60
        HENCE FULFILLED
        LEST
            PARTY `the Commissioner`
            MUST `issue a Required Steps Notice`
            WITHIN 14
            HENCE `the correction period`
            LEST BREACH BY `the Commissioner` BECAUSE "failed to issue notice"
    ELSE FULFILLED

-- After notice is issued, charity has time to correct
GIVETH A DEONTIC Actor Action
`the correction period` MEANS
    PARTY `the Charity`
    MUST `correct the deficiencies`
    WITHIN 30
    HENCE FULFILLED
    LEST BREACH BY `the Charity` BECAUSE "failed to correct after notice"

-- A prohibition: charities must not distribute profits to their governors
GIVETH A DEONTIC Actor Action
`the profit distribution prohibition` MEANS
    PARTY `the Charity`
    SHANT `distribute profits to the governors`
    HENCE FULFILLED
    LEST BREACH BY `the Charity` BECAUSE "distributed profits to governors"

Key patterns:

1. Actor and Action types: Define who can act and what actions exist
2. Conditional obligations: Only active charities must file
3. Chained obligations: Non-compliance triggers Commissioner action, then a correction period
4. Prohibitions with SHANT: what must NOT happen
5. Clear blame assignment: BREACH BY ... BECAUSE ...

---

Step 5: Create Test Data

-- Valid governor
`Jane Smith` MEANS Governor "Jane Smith" 45 FALSE (LIST)

-- Governor with issues
`John Doe (bankrupt)` MEANS Governor "John Doe" 50 TRUE (LIST)

`unspent conviction` MEANS Conviction "Fraud conviction 2020" FALSE
`Bob Jones (with conviction)` MEANS Governor "Bob Jones" 40 FALSE (LIST `unspent conviction`)

`Young Person` MEANS Governor "Young Person" 16 FALSE (LIST)

-- Valid charity
`Jersey Animal Welfare` MEANS `Registered Charity` "Jersey Animal Welfare" "CH001" Active (LIST `advancement of animal welfare`, `advancement of education`) (LIST `Jane Smith`)

-- Charity with invalid governor
`Problem Charity` MEANS `Registered Charity` "Problem Charity" "CH002" Active (LIST `advancement of education`) (LIST `John Doe (bankrupt)`)

-- Suspended charity
`Suspended Charity` MEANS `Registered Charity` "Suspended Charity" "CH003" (Suspended "Financial irregularities") (LIST `advancement of health`) (LIST `Jane Smith`)

Create governors and charities with various characteristics for testing—including ones that should fail.

---

Step 6: Test Everything

Unit Tests with #EVAL

#EVAL `the governor is an adult` `Jane Smith`                      -- TRUE
#EVAL `the person can be a governor` `Jane Smith`                  -- TRUE
#EVAL `the person can be a governor` `John Doe (bankrupt)`         -- FALSE
#EVAL `the person can be a governor` `Bob Jones (with conviction)` -- FALSE
#EVAL `the charity is valid` `Jersey Animal Welfare`               -- TRUE
#EVAL `the charity is valid` `Problem Charity`                     -- FALSE

#EVAL `the charity's size band` 60000                              -- "medium"
#EVAL `the annual filing fee` `Jersey Animal Welfare` 60000        -- 210

Scenario Tests with #TRACE

-- Happy path: charity files on time
#TRACE `the annual return obligation` `Jersey Animal Welfare` AT 0 WITH
    PARTY `the Charity` DOES `file the annual return` AT 30
-- Result: FULFILLED

-- Suspended charity: no filing required
#TRACE `the annual return obligation` `Suspended Charity` AT 0 WITH
-- Result: FULFILLED

-- Late filing: the charity misses the 60-day deadline (its day-65 filing
-- arrives too late), the Commissioner issues a notice, then the charity
-- corrects within the correction period
#TRACE `the annual return obligation` `Jersey Animal Welfare` AT 0 WITH
    PARTY `the Charity` DOES `file the annual return` AT 65
    PARTY `the Commissioner` DOES `issue a Required Steps Notice` AT 70
    PARTY `the Charity` DOES `correct the deficiencies` AT 90
-- Result: FULFILLED

-- Prohibition: distributing profits is a breach
#TRACE `the profit distribution prohibition` AT 0 WITH
    PARTY `the Charity` DOES `distribute profits to the governors` AT 10
-- Result: BREACH BY `the Charity` BECAUSE "distributed profits to governors"

---

Organizing Code with Sections

Use sections (§) to organize larger files:

§ `Charity Registration System`

§§ `Type Definitions`
-- Types go here

§§ `Eligibility Rules`
-- Eligibility functions go here

§§ `Filing Obligations`
-- Regulative rules go here

§§ `Tests`
-- Test cases go here

Sections create a hierarchy:

• § - Top-level section
• §§ - Sub-section
• §§§ - Sub-sub-section

---

Best Practices

1. Start with Types

-- ✅ Good: Clear domain model
DECLARE Application
    HAS `the applicant` IS A `Legal Entity`
        `the purposes` IS A LIST OF Purpose
        `the documents` IS A LIST OF Document

2. Small, Focused Functions

-- ✅ Good: Single responsibility
DECIDE `the governor is an adult` IF governor's `the governor's age` >= 18
DECIDE `the governor is not bankrupt` IF NOT governor's `the governor is bankrupt`

-- Combine them
DECIDE `the person can be a governor` IF
    `the governor is an adult` governor
    AND `the governor is not bankrupt` governor

3. Test Every Path

-- Happy path
#EVAL `the person can be a governor` `Jane Smith`             -- TRUE

-- Error cases
#EVAL `the person can be a governor` `John Doe (bankrupt)`    -- FALSE
#EVAL `the person can be a governor` `Young Person`           -- FALSE

4. Use Descriptive Names

-- ✅ Good: Clear, readable names
DECIDE `the charity meets filing requirements` IF ...

-- ❌ Bad: Cryptic names
DECIDE check1 IF ...

5. Document Complex Logic

-- The charity test requires:
-- 1. All purposes must be from the statutory list (Art 5)
-- 2. The charity must provide public benefit (Art 7)
-- 3. All governors must be fit and proper (Art 19)
DECIDE `meets charity test` IF ...

---

Debugging Checklist

When something doesn't work:

Error	Likely Cause	Fix
"Type not in scope"	Type not declared	Add DECLARE before use
"Unexpected 's"	Missing parentheses	count (x's field) not count x's field
"Expected BOOLEAN"	Wrong type in condition	Check IF conditions return BOOLEAN
"Not enough arguments"	Missing function args	Count parameters in GIVEN
"Indentation error"	Inconsistent spacing	Align all fields under HAS

---

Where to Go Next

Immediate Next Steps

1. Advanced Course - Complex patterns, real legislation, multi-instrument integration

2. Tutorials - Task-focused guides:

   • Building web forms
   • LLM integration
   • Contract automation

3. Practice - Try encoding a real document:

   • Your employment contract
   • Your lease agreement
   • A regulation you work with

Reference Materials

• Reference Guide - Complete keyword and syntax reference
• Concepts - Deep dives into design principles

Example Code

Explore the examples in the repository:

• jl4/examples/legal/ - Real legal documents
• jl4/examples/ok/ - Working syntax examples
• jl4/experiments/ - Experimental features

---

Summary: What You've Learned

Module 1: Your First Legal Rule

• GIVEN, PARTY, MUST
• IF conditions
• WITHIN deadlines
• HENCE and LEST consequences

Module 2: Legal Entities and Relationships

• DECLARE with HAS for records
• IS ONE OF for enumerations
• Field access with 's

Module 3: Control Flow

• IF/THEN/ELSE and BRANCH
• CONSIDER pattern matching
• AND, OR, NOT operators
• List operations

Module 4: Decision Logic

• Constitutive rules with DECIDE and MEANS
• WHERE for transparent calculations
• Optional values with MAYBE (NOTHING/JUST)
• Working with dates

Module 5: Functions

• GIVEN and GIVETH signatures
• Recursion
• Higher-order functions: map, filter, foldl

Module 6: Regulative Rules

• MUST, MAY, SHANT
• HENCE, LEST
• PROVIDED conditions
• RAND and ROR combinators
• #TRACE testing

Module 7: Putting It Together

• Project structure
• Best practices
• Debugging

---

Congratulations! 🎉

You've completed the L4 Foundation Course. You now have the skills to:

• Model legal entities and relationships
• Write legal rules and eligibility criteria
• Create contracts with obligations and consequences
• Test your models with simulations

Next recommended step: Try the Advanced Course to learn about real regulatory schemes, cross-cutting concerns, and production patterns.