https://blog.rafaelfernandez.dev/tags/traits/ Recent content in Traits on Home Hugo -- gohugo.io en © 2026 Rafael Fernandez Tue, 03 Mar 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/tagless-final-is-denotational-semantics/ Tue, 03 Mar 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/tagless-final-is-denotational-semantics/ Every trait in your hexagonal architecture is a tagless-final algebra. Every impl is an interpreter. You have been writing denotational semantics without knowing it. We trace the connection from Kiselyov’s paper through Scala’s Cats-Effect to Rust’s port traits, and show why the pattern that academics call ‘finally tagless’ is the same pattern that practitioners call ‘dependency injection.’ https://blog.rafaelfernandez.dev/posts/syntax-and-semantics-3-the-expression-problem/ Sat, 07 Feb 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/syntax-and-semantics-3-the-expression-problem/ Adding a new type is easy in OOP, hard in FP. Adding a new operation is easy in FP, hard in OOP. Philip Wadler named this the Expression Problem in 1998. We show how it manifests in Rust and Scala, and tease the resolution. https://blog.rafaelfernandez.dev/posts/syntax-and-semantics-2-three-ways-to-define-meaning/ Tue, 03 Feb 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/syntax-and-semantics-2-three-ways-to-define-meaning/ Your match expression is operational semantics. Your pure function is denotational semantics. Rust’s borrow checker is axiomatic semantics. Three formal frameworks, three ways to assign meaning to code, and you have been using all of them without knowing it. https://blog.rafaelfernandez.dev/posts/traits-are-grammars-too-from-contract-design-to-formal-syntax/ Wed, 28 Jan 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/traits-are-grammars-too-from-contract-design-to-formal-syntax/ While revisiting the TaskRepository trait from the Todo CLI series, I realized I was doing more than drawing an architectural boundary. I was also defining what could be said across that boundary, which is much closer to grammar than I first admitted. https://blog.rafaelfernandez.dev/posts/todo-cli-rust-3-json-persistence-contract-vs-implementation/ Thu, 15 Jan 2026 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/todo-cli-rust-3-json-persistence-contract-vs-implementation/ Third part of the series: we define the persistence contract with a generic trait, implement two adapters (in-memory and JSON to disk), and delve into the difference between interface and implementation as the axis of hexagonal architecture. https://blog.rafaelfernandez.dev/posts/the-forge-of-typeclasses/ Mon, 17 Mar 2025 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/the-forge-of-typeclasses/ We explore in detail what typeclasses are, how to define them in Scala 2, and how they are implemented in other languages such as Haskell and Rust. Through practical examples, we demonstrate how to model behaviors clearly and scalably using this powerful design pattern in functional programming. We also discuss automatic derivation and the improvements Scala 3 brings to this area. https://blog.rafaelfernandez.dev/posts/one-typeclass-to-rule-them-all/ Mon, 10 Mar 2025 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/one-typeclass-to-rule-them-all/ We analyzed different functional pattern designs to address the abstraction of a functionality and its implementation. https://blog.rafaelfernandez.dev/posts/first-steps-in-rust/ Thu, 13 Feb 2025 00:00:00 +0000 https://blog.rafaelfernandez.dev/posts/first-steps-in-rust/ My first impressions of Rust from a functional programming background (Scala and Haskell). A mix of excitement, frustration, and a paradigm shift in thinking.