Typing and semantics of asynchronous arrows in JavaScript

Asynchronous programs in JavaScript using callbacks and promises are di cultto write correctly. Many programs have subtle errors due to the unwantedinteraction of event handlers. To x such errors, the programmer is burdenedwith explicit registration and de-registration of event handlers. This producesfragile code which is di cult to read and maintain.Arrows, a generalization of monads, are an elegant solution to asynchronousprogram composition. In this paper, we present the semantics of an arrow-basedDSL in JavaScript which can encode asynchronous programs as a state machinewhere edge transitions are triggered by external events. To ensure that arrowsare composed correctly, we provide an optional type checker that reports errorsbefore the machine begins execution.