Encoding Legislation

Turn a legal provision into L4 code.

Audience: Legal professionals, legal engineers
Prerequisites: Basic L4 knowledge (Your First L4 File)
Time: 30 minutes
Goal: Encode a real legal provision as executable L4 rules

What You'll Build

We'll encode this provision from an imaginary Alcohol Act:

Section 3. A person must not sell alcohol if: (a) the person is a body corporate; (b) the person engages in business for profit; (c) the person is not a public house or hotel; and (d) any of the following applies: (i) the person has an unspent conviction for fraud; (ii) the person has an unspent conviction for providing misleading information; or (iii) the person has an alcohol banning order.

Step 1: Analyze the Structure

Before writing code, identify:

Outcome: "must not sell alcohol"
Conditions: (a), (b), (c), (d) - all must be true
Sub-conditions: (d)(i), (d)(ii), (d)(iii) - any one triggers

The logical structure:

(a) AND (b) AND (c) AND ((d)(i) OR (d)(ii) OR (d)(iii))

Step 2: Declare the Inputs

First, declare the facts we need. These are assumptions because their truth comes from outside L4:

§ `Imaginary Alcohol Act - Section 3`

-- Facts about the person
ASSUME `the person is a body corporate` IS BOOLEAN
ASSUME `the person engages in business for profit` IS BOOLEAN
ASSUME `the person is a public house` IS BOOLEAN
ASSUME `the person is a hotel` IS BOOLEAN

-- Criminal history and orders
ASSUME `the person has an unspent conviction for fraud` IS BOOLEAN
ASSUME `the person has an unspent conviction for providing misleading information` IS BOOLEAN
ASSUME `the person has an alcohol banning order` IS BOOLEAN

Why ASSUME?

ASSUME declares facts that come from outside L4:

User input
Database lookup
Another system

L4 doesn't know or check these values—it just uses them.

Step 3: Encode the Rule

Now translate the legal text directly:

-- Section 3: Prohibition on selling alcohol
DECIDE `the person must not sell alcohol`
IF  `the person is a body corporate`
    AND `the person engages in business for profit`
    AND NOT `the person is a public house`
    AND NOT `the person is a hotel`
    AND (
        `the person has an unspent conviction for fraud`
        OR `the person has an unspent conviction for providing misleading information`
        OR `the person has an alcohol banning order`
    )

Matching the Legal Text

Notice how the L4 mirrors the legislation:

Legal Text	L4 Code
"the person is a body corporate"	`\`the person is a body corporate``
"the person is not a public house or hotel"	`NOT \`..is a public house` AND NOT `..is a hotel``
"any of the following applies"	`(...OR...OR...)`

Step 4: Add Test Cases

Test the rule with specific scenarios:

§ `Test Cases`

{-
Scenario 1: Corporate pub (exempt)
- Body corporate: Yes
- For profit: Yes
- Public house: Yes (exempt!)
Expected: FALSE (not prohibited because it's a public house)
-}
#CHECK `the person must not sell alcohol` WITH
    `the person is a body corporate` IS TRUE,
    `the person engages in business for profit` IS TRUE,
    `the person is a public house` IS TRUE,
    `the person is a hotel` IS FALSE,
    `the person has an unspent conviction for fraud` IS TRUE,
    `the person has an unspent conviction for providing misleading information` IS FALSE,
    `the person has an alcohol banning order` IS FALSE

{-
Scenario 2: Banned corporate (prohibited)
- Body corporate: Yes
- For profit: Yes
- Public house: No
- Hotel: No
- Banning order: Yes
Expected: TRUE (prohibited)
-}
#CHECK `the person must not sell alcohol` WITH
    `the person is a body corporate` IS TRUE,
    `the person engages in business for profit` IS TRUE,
    `the person is a public house` IS FALSE,
    `the person is a hotel` IS FALSE,
    `the person has an unspent conviction for fraud` IS FALSE,
    `the person has an unspent conviction for providing misleading information` IS FALSE,
    `the person has an alcohol banning order` IS TRUE

{-
Scenario 3: Clean corporate (not prohibited)
- Body corporate: Yes
- For profit: Yes
- No exemption, but no disqualifying factors
Expected: FALSE (not prohibited - no (d) condition met)
-}
#CHECK `the person must not sell alcohol` WITH
    `the person is a body corporate` IS TRUE,
    `the person engages in business for profit` IS TRUE,
    `the person is a public house` IS FALSE,
    `the person is a hotel` IS FALSE,
    `the person has an unspent conviction for fraud` IS FALSE,
    `the person has an unspent conviction for providing misleading information` IS FALSE,
    `the person has an alcohol banning order` IS FALSE

Step 5: Refactor for Readability

For complex rules, break into named sub-rules:

§ `Refactored Version`

-- Sub-rule: Is this a commercial enterprise?
DECIDE `is commercial enterprise`
IF  `the person is a body corporate`
    AND `the person engages in business for profit`

-- Sub-rule: Is this an exempt establishment?
DECIDE `is exempt establishment`
IF  `the person is a public house`
    OR `the person is a hotel`

-- Sub-rule: Does person have disqualifying factors?
DECIDE `has disqualifying factors`
IF  `the person has an unspent conviction for fraud`
    OR `the person has an unspent conviction for providing misleading information`
    OR `the person has an alcohol banning order`

-- Main rule: Prohibition (refactored)
DECIDE `the person must not sell alcohol (refactored)`
IF  `is commercial enterprise`
    AND NOT `is exempt establishment`
    AND `has disqualifying factors`

This version is easier to understand and maintain.

Step 6: Add Documentation

Link back to the source legislation:

{-
Imaginary Alcohol Act 2024
==========================

Section 3 - Prohibition on Sale of Alcohol

This section implements the prohibition in s.3 which prevents
certain commercial entities from selling alcohol if they have
disqualifying factors (fraud, misleading info, or banning orders).

Exemptions:
- Public houses (s.3(c))
- Hotels (s.3(c))

Note: "unspent conviction" follows the Rehabilitation of Offenders
Act interpretation - see s.2 for definitions.
-}

Complete Example

Here's the full file:

§ `Imaginary Alcohol Act - Section 3`

{-
Implements Section 3 of the Imaginary Alcohol Act 2024.
Determines whether a person is prohibited from selling alcohol.
-}

-- External facts (from user input or database)
ASSUME `the person is a body corporate` IS BOOLEAN
ASSUME `the person engages in business for profit` IS BOOLEAN
ASSUME `the person is a public house` IS BOOLEAN
ASSUME `the person is a hotel` IS BOOLEAN
ASSUME `the person has an unspent conviction for fraud` IS BOOLEAN
ASSUME `the person has an unspent conviction for providing misleading information` IS BOOLEAN
ASSUME `the person has an alcohol banning order` IS BOOLEAN

§§ `Sub-rules`

DECIDE `is commercial enterprise`
IF  `the person is a body corporate`
    AND `the person engages in business for profit`

DECIDE `is exempt establishment`
IF  `the person is a public house`
    OR `the person is a hotel`

DECIDE `has disqualifying factors`
IF  `the person has an unspent conviction for fraud`
    OR `the person has an unspent conviction for providing misleading information`
    OR `the person has an alcohol banning order`

§§ `Main Rule`

DECIDE `the person must not sell alcohol`
IF  `is commercial enterprise`
    AND NOT `is exempt establishment`
    AND `has disqualifying factors`

§§ `Tests`

-- Exempt: public house
#CHECK NOT `the person must not sell alcohol` WITH
    `the person is a body corporate` IS TRUE,
    `the person engages in business for profit` IS TRUE,
    `the person is a public house` IS TRUE,
    `the person is a hotel` IS FALSE,
    `the person has an unspent conviction for fraud` IS TRUE,
    `the person has an unspent conviction for providing misleading information` IS FALSE,
    `the person has an alcohol banning order` IS FALSE

-- Prohibited: has banning order
#CHECK `the person must not sell alcohol` WITH
    `the person is a body corporate` IS TRUE,
    `the person engages in business for profit` IS TRUE,
    `the person is a public house` IS FALSE,
    `the person is a hotel` IS FALSE,
    `the person has an unspent conviction for fraud` IS FALSE,
    `the person has an unspent conviction for providing misleading information` IS FALSE,
    `the person has an alcohol banning order` IS TRUE

Tips for Encoding Legislation

1. Preserve Legal Language

Use the exact terms from the legislation where possible:

-- ✅ Good: matches statute
ASSUME `the person is a body corporate` IS BOOLEAN

-- ❌ Less good: paraphrased
ASSUME isCompany IS BOOLEAN

2. Handle "And/Or" Carefully

Legal "or" is often inclusive (any one or more):

-- "A, B, or C" usually means "A OR B OR C"
condition1 OR condition2 OR condition3

3. Watch for Implicit Negation

"not a public house or hotel" can be ambiguous:

-- Could mean: NOT (public house OR hotel)
NOT (`is public house` OR `is hotel`)

-- Or: (NOT public house) OR (NOT hotel)  -- usually not intended

4. Test Edge Cases

All conditions true
All conditions false
Each exemption independently
Each disqualifying factor independently

What You Learned

How to analyze legal text structure
How to use ASSUME for external facts
How to encode AND/OR conditions
How to refactor for readability
How to test legislative rules

Next Steps

Common Patterns - More L4 patterns
Foundation Course Module 1 - Deep dive on legal rules
LLM Integration - LLM-assisted encoding