一句话:提出递归的广义模态,将 Nakano 的 later modality 推广到更一般的范畴框架。
Nakano 的 later modality 使类型能够表达函数输出不立即依赖其输入,从而保证不动点的计算安全,这一思想称为 guarded recursion,已用于无限数据结构与类型论内部的 step-indexing 等场景。本文研究递归的广义模态,并借助范畴模型说明 later modality 本质上对应于离散时间尺度上的一种重新索引。由此,论文将 later modality 与 guarded recursion 置于更一般的范畴与类型论框架中,为递归模态提供统一视角。摘要未报告具体实验评估,论证主要基于范畴模型分析。
Nakano's later modality allows types to express that the output of a function does not immediately depend on its input, and thus that computing its fixpoint is safe. This idea, guarded recursion, has proved useful in various contexts, from functional programming with infinite data structures to formulations of step-indexing internal to type theory. Categorical models have revealed that the later modality corresponds in essence to a simple reindexing of the discrete time scale.