Journal of Information Processing
Online ISSN : 1882-6652
ISSN-L : 1882-6652
Lightweight Linearly-typed Programming with Lenses and Monads
Keigo ImaiJacques Garrigue
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2019 Volume 27 Pages 431-444


This paper shows an encoding of linear types in OCaml and its applications. The encoding enables to write correct OCaml programs based on safe resource access guided by linear types. Linear types ensure that every variable is used exactly once, and, thus, they can be used to check the behavioural aspects of programs such as resource access and communication protocols in a static way. However, linear types require significant effort to be integrated into existing programming languages. Our encoding allows the vanilla OCaml typechecker to enforce linearity by using lenses and a parameterised monad. Parameterised monads are monads with a pre- and a post-condition, and we use them to track the creation and consumption of resources at the type level. Lenses, which point at parts of a data type, are used to refer to a resource in pre- and post-conditions. To handle comfortably structured data such as linearly typed lists, we further propose an extension to pattern matching based on the syntax-extension mechanism of OCaml. We show an application to static checking of communication protocols in OCaml.

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© 2019 by the Information Processing Society of Japan
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