Event-lang

Synchronizable Event Programming

Event-lang is an experimental Racket library that simplifies the creation of complex synchronizable events.

Event-lang provides a primitive expression lifting form,

> (pure 123)
#<evt>

some event combinators,

> (sync (fmap + (pure 1) (pure 2)))
3
> (sync (app (pure +) (pure 1) (pure 2)))
3
> (sync (bind (pure 1) (pure 2) (λ xs (pure (apply + xs)))))
3

and a collection of event-friendly alternatives to base Racket forms and functions.

> (sync
   (event-let
    ([x (pure 1)]
     [y (pure 2)])
    (pure (list x y))))
'(1 2)

Composite events make progress by synchronizing constituent events, either concurrently or in a predictable sequence. Synchronization results can be ordered as specified,

> (let ([t0 (current-inexact-milliseconds)])
    (define (now) (- (current-inexact-milliseconds) t0))
    (sync
     (async-args
      (pure (cons 1 (now)))
      (pure (cons 2 (now)))
      (pure (cons 3 (now))))))
'(1 . 0.200927734375)
'(2 . 0.14990234375)
'(3 . 0.178955078125)

or as completed.

> (let ([t0 (current-inexact-milliseconds)])
    (define (now) (- (current-inexact-milliseconds) t0))
    (sync
     (async-set
      (pure (cons 1 (now)))
      (pure (cons 2 (now)))
      (pure (cons 3 (now))))))
'(2 . 0.0771484375)
'(3 . 0.093017578125)
'(1 . 0.123046875)

The project has three outstanding objectives:

Provide a sophisticated lifting form to simplify usage of the provided constructs. The event/event module contains a first approximation. Its construction was tedious and error prone, so I commented out the docs.
Provide a full-blown #lang event/racket/base for producing whole modules of events and event constructors from ordinary Racket code in a principled manner.
Provide support for static analysis of synchronization behaviors. Event programming in Racket is a curious form of meta-programming, and a few simple compile-time checks could reduce cognitive overhead.

dedbox/racket-event

Event-lang