L4 with IDE

An implementation of the L4 language for law, with an emphasis on IDE extensions for Visual Studio Code, and a web-only version of the L4 editor.

This repository includes language examples, a compiler toolchain, a visualizer, and integrations with VS Code.

Gallery

Syntax Highlighting for Boolean-oriented decision logic

Decision Logic Visualization as a ladder diagram circuit

Status (25 Feb 2025)

• ✅ Basic language features (functional core, layout parsing)
• ✅ Basic IDE features (highlighting, CHECK, EVAL)
• ✅ Decision logic visualizer (as ladder diagram)
• 🚧 resource libraries for Date, Place, Entity, Currency
• 🚧 Language support for state transition modals
• 🚧 State transition logic visualizer
• 🚧 Web App Auto-Generation for Decision Logic
• 🚧 Web App Auto-Generation for State Transition Logic, abductive reasonign, planning problems
• 🚧 Formal Verification Tooling, enhanced compiler error messages and warnings

The Web Editor

An experimental prototype offers a lightweight web-based alternative to VS Code.

https://jl4.well-typed.com/

VS Code Extension: Download, Install and Build

Dev Build: for Haskell and JS developers to improve the toolchain and IDE developer experience. Requires Haskell and Typscript.

Quickstart for a local build: for legal engineers to experiment with writing L4 code locally. Download the VS Code extension and get started.

Language Tutorials

All this documentation is still under construction.

• Tutorial: Hello, World

  • The DECIDE stanza
  • The ASSUME environment
  • Term Substitution
  • Example: Must Sing
  • Example: The Dog Act
  • Example: Vermin

• Tutorial: British Nationality Act

  • Default Logic and Optional types with the Maybe monad
  • References and Legal Citations
  • Temporals

• Tutorial: Automatically Building User-Facing Apps

• Tutorial: Automatically Generating an AI Chatbot

• Tutorial: Contracts involving Parties, Obligations, and Deadlines

  • visualizing a contract
  • abductive reasoning and planning problems

• Tutorial: Automatically Finding Loopholes

  • underspecification, vagueness, and ambiguity

Language Reference

• Decision Logic

• State Transitions

• Functional and Logical Paradigms

• Source Citations and Versioning

• Multi-Temporal Logic

  • a remark on "shall" as an unfortunate consequence of negotiation-time vs run-time interpretation

• Operationalization to Web and Mobile Apps

• Natural Language Generation: exporting to Word and PDF