Our paper “Effects as Capabilities: Effect Handlers and Lightweight Effect Polymorphism” (Jonathan Brachthäuser
AlumniJonathan Immanuel Brachthäuser, Philipp Schuster
AlumniPhilipp Schuster and Klaus Ostermann
HeadKlaus Ostermann ) has been accepted for publication at the International Conference on Object Oriented Programming Systems Languages & Applications (OOPSLA, 2020).

Abstract

Effect handlers have recently gained popularity amongst programming language researchers. Existing type- and effect systems for effect handlers are often complicated and potentially hinder a wide-spread adoption. We present the language Effekt with the goal to close the gap between research languages with effect handlers and languages for working programmers. The design of Effekt revolves around a different view of effects and effect types. Traditionally, effect types express which side effects a computation might have. In Effekt, effect types express which capabilities a computation requires from its context. While this new point in the design space of effect systems impedes reasoning about purity, we demonstrate that it simplifies the treatment of effect polymorphism and the related issues of effect parametricity and effect encapsulation. To guarantee effect safety, we separate functions from values and treat all functions as second-class. We define the semantics of Effekt as a translation to System Xi, a calculus in explicit capability-passing style.

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Further Information

• Website of the Effekt language
• Extended technical report
• Implementation on github

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