一句话：提出严格函数式语言 Frank，用双向效果类型系统与推广的函数抽象统一 effect handlers，并引入 adaptor 支持效果封装与重连。
本文探索严格函数式语言 Frank 的设计与实现，目标是为模块化效应编程提供更自然的基础。传统 effect handler 虽能由类型静态追踪命令接口，却需要额外的处理构造，并常在源码中引入效应变量。Frank 将函数抽象推广为 operator：函数是不解释任何命令的特例，operator 可同时解释来自多个来源的命令，即 multihandler，从而保持直接风格。其双向效应类型系统让环境能力向内传播，避免源码中出现效应变量，并支持效应封装与库组件之间的重连；论文提出 adaptor 来消除 effect pollution。评估以语言设计、实现与未来可能性探讨为主，特别是与更丰富类型系统的结合。
Abstract 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 but 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 avoids mentioning effect variables in source code. This is achieved by propagating an ambient ability inwards, rather than accumulating unions of potential effects outwards. With the ambient ability describing the effects that are available at a certain point in the code, it can become necessary to reconfigure access to the ambient ability. A primary goal is to be able to encapsulate internal effects, eliminating a phenomenon we call effect pollution . Moreover, it is sometimes desirable to rewire the effect flow between effectful library components. We propose adaptors as a means for supporting both effect encapsulation and more general rewiring. 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 systems.