Most resources on nix flakes, however, assume you're starting a project from scratch. They don't give you much guidance about how to convert an existing nix project to flakes.
In this blog post, we'll do just that. With a further constraint: we'll keep the project working as a legacy nix project, and with relatively minimal changes. That way, people who prefer flakes can use flakes, people who don't can use legacy nix.
In the Zed project, we’ve developed a command-line tool called zq (and, yes, the name “zq” is a play on “jq”) that is based on an orthogonal set of dataflow operators.
Zed operators are like jq filters but they can be stateful. To make this work, we simply borrowed the aggregate function concept from the 50 year-old SQL model, though unlike SQL, Zed aggregate functions can stream their results incrementally.
In short, zq is based on stateful dataflow while jq is based on stateless dataflow.
Source: Introducing zq: an Easier (and Faster) Alternative to jq.
A typeclass defines a set of methods that is shared across multiple types.
For a type to belong to a typeclass, it needs to implement the methods of that typeclass. These implementations are ad-hoc: methods can have different implementations for different types.
Source: Introduction to Haskell Typeclasses, an article by Gints Dreimanis.