The Deon Digital CSL Language Guide

This is an introduction to and overview of Deon Digital’s Contract Specification Language (CSL). As the name implies, CSL is used to specify contracts – details such as the particular execution method or how participating parties are authenticated/validated are deliberately not included in the CSL specification.

This guide is also available as a single PDF file here.

If you encounter any problems, don’t hesitate to contact us at support@deondigital.com.

Introduction

For an introduction to the CSL language with a simple walk-through of your first contract and explanation of the basic concepts, start here:

• Contracts 101
• Your first CSL contract
  • Specifying events
  • Encoding events
  • Specifying the desired behaviour
• Contract life cycle
  • Instantiating contracts
  • Submitting events to contracts
  • Querying past state
  • Contracts observing the past of other contracts
• Guideline for using Deon Digital’s GUI
  • Composer
  • Viewer
  • Actions
  • Reports

Reference

The following chapters are useful as reference once you know the basic concepts:

• Contract language reference
  • The successfully completed contract
  • The breached contract
  • The prefixed-contract
  • Sequentially composed contracts
  • Concurrently composed contracts
  • Choice between contracts
  • Contract templates
  • Recursive contract templates
  • Contract abbreviations
• Value expression language
  • Primitive values and value literals
  • Operators
  • Constructors and sum types
  • List shorthand
  • Records
  • Functions
  • Conditional expressions (if-then-else)
  • Type case expressions
  • Upcast annotation
  • Let-expressions
  • Type annotations
  • Equality checking
• Modules
• Scoping
  • Sequential bindings
  • Simultaneous bindings
  • Local scopes
  • Recursive bindings
  • Overview
• Report query language
  • Overview
  • Relations
  • for expressions
• The CSL Standard Library
  • Functions operating on numbers
  • String functions
  • Boolean functions
  • Time and date functions
  • Duration functions
  • Signed functions
  • General combinators
  • Tuple
  • Maybe
  • Ordering
  • List
  • Event
  • Built-in functions and types
  • CSL standard library source code
• CSL grammar

Tooling

In this chapter we introduce the code generation tool sic and describe how to use it:

• The sic boilerplate generator
  • Overview
  • Using Kotlin as the target language
  • Using TypeScript as the target language
  • Emit JSON representation of core AST
  • Emit JSON representation of contract structure
  • Projects with multiple CSL files

Examples

For various examples look in these chapters:

• Example reports
  • Events filtering
  • Custom data structures
  • Complex reports
• Examples of CSL contracts
  • Delivery deadline relative to payment
  • Late payment
  • Partial payments
  • Escrow
  • Transferable contract
  • Signing contracts
  • Past events
  • Modules

Exercises

Some more advanced exercises and solutions to most exercises presented in this guide:

• Exercises
  • Writing and running contracts
  • Expressions and reports
• Solutions
  • Solution: Pay on delivery
  • Solution: Pay or return
  • Solution: Bike and helmet
  • Solution: Late payment
  • Solution: Age-restricted purchase
  • Solution: Shopping basket
  • Solution: Two-buyer protocol
  • Solution: Bank account balance
  • Solution: Reimbursement for business travel