Pappe

An embedded interpreted synchronous DSL for Swift.

Background

This Swift Package allows you to experiment with synchronous programming in Swift. It follows the imperative synchronous programming language Blech and tries to recreate parts of it as an embedded interpreted DSL using the Swift functionBuilders.

The imperative synchronous approach allows preemption and concurrency in a structured and modular way.

Usage

In this usage example three trails run concurrently for 10 ticks as determined by the first strong trail before printing "done". The second trail prints a message every third tick and the last trail every second tick.

let m = Module { name in
    activity (name.Wait, [name.ticks]) { val in
        exec { val.i = val.ticks as Int }
        while { val.i > 0 } repeat: {
            exec { val.i -= 1 }
            await { true }
        }
    }
    activity (name.Main, []) { val in
        cobegin {
            strong {
                run (name.Wait, [10])
            }
            weak {
                `repeat` {
                    run (name.Wait, [2])
                    exec { print("on every third") }
                    await { true }
                }
            }
            weak {
                `repeat` {
                    run (name.Wait, [1])
                    exec { print("on every second") }
                    await { true }
                }
            }
        }
        exec { print("done") }
    }
}

For more extensive code examples, please have a look at:

• Unit Tests
• BlinkerPappe project. The Pappe code can be found in this file.
• The Synchrosphere project as well as the SynchrosphereDemo App which allows to control Sphero robots via imperative synchronous code.

The documentation of the SynchrosphereDemos can be seen as a tutorial for the Pappe language, as it explains its language constructs with concrete examples.

Caveats

The Pappe DSL is more of a proof of concept. It has many shortcomings like:

• No causality checking.
• Interpreted instead of compiled.
• Untyped and unchecked variables.
• Poor Test coverage.