Freer monads, more extensible effects

KiselyovOleg,; Ishii, Hiromi

doi:10.1145/2887747.2804319

Cited by 39 publications

(40 citation statements)

References 25 publications

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“…For instance, user and kernel monads are implemented as corresponding Haskell monads. Internally the library uses the Freer monad of Kiselyov [13] to implement free model monads for given signatures of operations. The library also provides a means to run user code via Haskell's top-level monads.…”

Section: Methodsmentioning

confidence: 99%

Runners in Action

Ahman

Bauer

2020

Programming Languages and Systems

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Runners of algebraic effects, also known as comodels, provide a mathematical model of resource management. We show that they also give rise to a programming concept that models top-level external resources, as well as allows programmers to modularly define their own intermediate "virtual machines". We capture the core ideas of programming with runners in an equational calculus λcoop, which we equip with a sound and coherent denotational semantics that guarantees the linear use of resources and execution of finalisation code. We accompany λcoop with examples of runners in action, provide a prototype language implementation in OCaml, as well as a Haskell library based on λcoop.

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Section: Methodsmentioning

confidence: 99%

Runners in Action

Ahman

Bauer

2020

Programming Languages and Systems

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“…Algebraic effect handlers, introduced by Plotkin and Pretnar [21], make it possible to provide user-defined effects. Algebraic effect handlers have been gaining popularity owing to their flexibility and have been made available as libraries [13,26,15] or as primitive features of languages, such as Eff [3], Koka [16], Frank [18], and Multicore OCaml [5]. In these languages, let-bound expressions that can be polymorphic are restricted to values or pure expressions.…”

Section: Algebraic Effects and Handlersmentioning

confidence: 99%

Handling Polymorphic Algebraic Effects

Sekiyama

Igarashi

2019

Lecture Notes in Computer Science

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Algebraic effects and handlers are a powerful abstraction mechanism to represent and implement control effects. In this work, we study their extension with parametric polymorphism that allows abstracting not only expressions but also effects and handlers. Although polymorphism makes it possible to reuse and reason about effect implementations more effectively, it has long been known that a naive combination of polymorphic effects and let-polymorphism breaks type safety. Although type safety can often be gained by restricting let-bound expressions-e.g., by adopting value restriction or weak polymorphismwe propose a complementary approach that restricts handlers instead of let-bound expressions. Our key observation is that, informally speaking, a handler is safe if resumptions from the handler do not interfere with each other. To formalize our idea, we define a call-by-value lambda calculus λ let eff that supports let-polymorphism and polymorphic algebraic effects and handlers, design a type system that rejects interfering handlers, and prove type safety of our calculus.

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“…Their work explains how Kammar et al [25] implemented efficient handler code in Haskell. Kiselyov and Ishii [26] optimise their shallow effect handlers implementation, which is based on free monads, by taking advantage of an efficient representation of sequences of monadic operations [58]. The experimental multicore extension to OCaml [12] extends OCaml with effect handlers motivated by a desire to abstract over scheduling strategies.…”

Section: Related Workmentioning

confidence: 99%

“…They attempt to tackle the problem of how to modularly weave an effect handler through a computation whose commands may themselves be parameterised by other computations. Kiselyov and Ishii [26] provide solutions to particular instances of this problem. Schrijvers et al [51] apply effect handlers to logic programming.…”

Section: Layered Monads and Monadic Reflectionmentioning

confidence: 99%

“…Moreover, although there are a number of ways of almost simulating effect type systems in Haskell, none is without its flaws. Kiselyov and collaborators [26,27] have built another Haskell library for effect handlers, making different design choices.Brady's effects library [8] provides a DSL for programming with effects in the dependently typed language Idris [9]. Like the Haskell libraries, Brady's library currently requires the programmer to write effectful code in a monadic style.McBride's Shonky [41] is essentially an untyped version of Frank, with a somewhat different concrete syntax.…”

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Do be do be do

LindleySam¹,

McBrideConor²,

McLaughlinCraig³

2017

SIGPLAN Not.

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We explore the design and implementation of Frank, a strict functional programming language with a bidirectional effect type system designed from the ground up around a novel variant of Plotkin and Pretnar's effect handler abstraction.Effect handlers provide an abstraction for modular effectful programming: a handler acts as an interpreter for a collection of commands whose interfaces are statically tracked by the type system. However, Frank eliminates the need for an additional effect handling construct by generalising the basic mechanism of functional abstraction itself. A function is simply the special case of a Frank operator that interprets no commands. Moreover, Frank's operators can be multihandlers which simultaneously interpret commands from several sources at once, without disturbing the direct style of functional programming with values.Effect typing in Frank employs a novel form of effect polymorphism which avoid mentioning effect variables in source code. This is achieved by propagating an ambient ability inwards, rather than accumulating unions of potential effects outwards.We introduce Frank by example, and then give a formal account of the Frank type system and its semantics. We introduce Core Frank by elaborating Frank operators into functions, case expressions, and unary handlers, and then give a sound small-step operational semantics for Core Frank.Programming with effects and handlers is in its infancy. We contribute an exploration of future possibilities, particularly in combination with other forms of rich type system. Hillerström and Lindley [20-22] (Links [11]) and Leijen [30] (Koka [29]) have extended existing languages with effect handlers and algebraic effects. Both languages incorporate row-based effect type systems and attempt to elide some effect variables from source code, but neither eliminates effect variables to the extent that Frank does. Dolan et al. [12] built Multicore OCaml by extending OCaml with support for effect handlers and algebraic effects. Multicore OCaml does not include an effect type system.Whereas Frank is bidirectionally typed, all of these other languages use Hindley-Milner type inference. None of the other languages supports multihandlers and none of those with effect typing allow effect variables to be omitted to the degree that Frank does.Kammar et al.[25] describe a number of effect handler libraries for languages ranging from Racket, to SML, to OCaml, to Haskell. Apart from the Haskell library, their libraries have no effect typing support. The Haskell library takes advantage of type classes to simulate an effect type system not entirely dissimilar to that of Frank. As Haskell is lazy, the Haskell library cannot be used to write direct-style effectful programs-one must instead adopt a monadic style. Moreover, although there are a number of ways of almost simulating effect type systems in Haskell, none is without its flaws. Kiselyov and collaborators [26,27] have built another Haskell library for effect handlers, making different design choices.Brady's effe...

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Freer monads, more extensible effects

Cited by 39 publications

References 25 publications

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Handling Polymorphic Algebraic Effects

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