Live programming brings code to life with immediate and continuous feedback. To enjoy its benefits, programmers need powerful languages and live programming environments for understanding the effects of coding actions and developing running programs. We aim to deliver the enabling technology that powers these languages. We introduce Cascade, a meta-language and framework for expressing languages with interface- and feedback-mechanisms that drive live programming. [paper] [slides] [presentation recording]

The Cascade framework consists of a compiler and a runtime that help developers in constructing language back-ends. Its sources are avaiable under the 3-clause BSD license.

• TEL. Transformation Effect Language (TEL) is the working title of the Cascade compiler. This compiler is based on Rascal, a language workbench and meta-programming language. https://www.rascal-mpl.org

• Delta. Detla is a virtual machine based on C# for running Cascade programs. When executing user actions or coding actions, Delta generates cause-and-effect chains as transactions of edit operations in response. As a result, it can account for run-time eventualities such as run-time state migrations. The built-in REPL is the default interface for interacive coding and user interaction.

• DSLs. Cascade can be used to create Live Domain-Specific Languages (DSLs). Tiny Live State Machine Language (TinyLiveSML) is included as a demo. We describe a live programming scenario below. Other DSLs currently under development are the Questionnaire Language, Machinations and Behavior Trees.

Cascade includes an Integrated Development Environment for creating programming languages. Running TEL requires installing Rascal and importing the project. Integrating TEL into the Eclipse IDE requires running the following commands.

import lang::tel::IDE;
tel_register();

Cascade offers a compiler for transforming TEL sources into C# code. Running the compiler for TinyLiveSML requires the following commands

import lang::tel::Compiler;
compile(|project://TEL/models/TinyLiveSML|);

The C# sources will be generated into TEL/generated/Delta/TinyLiveSML.

Code generated by the TEL compiler integrates with Delta's sources. For compiling the sources we have used JetBrains Rider. Delta's serves its web-based user interface on http://127.0.0.1:8000

We demo a live programming scenario with TinyLiveSML.

• First we create a TinyLiveSML program of a door that can open and close. [part 1]
• Next, we run this program. [part 2]
• Finally, we delete the current state and observe TinyLiveSML migrates the run-time state. [part 3]