Typed Design Patterns for the Functional Era

TL;DR

This paper revisits design patterns in the context of functional programming, demonstrating how Rust's type system can encode domain concepts to improve correctness and expressiveness.

Contribution

It introduces a new approach to design patterns tailored for functional languages, exemplified by four patterns implemented in Rust to enhance compile-time safety.

Findings

Rust implementations effectively model domain concepts

Type systems can catch errors at compile-time

Enhanced pattern expressiveness in functional programming

Abstract

This paper explores how design patterns could be revisited in the era of mainstream functional programming languages. I discuss the kinds of knowledge that ought to be represented as functional design patterns: architectural concepts that are relatively self-contained, but whose entirety cannot be represented as a language-level abstraction. I present four concrete examples embodying this idea: the Witness, the State Machine, the Parallel Lists, and the Registry. Each pattern is implemented in Rust to demonstrate how careful use of a sophisticated type system can better model each domain construct and thereby catch user mistakes at compile-time.