Edward Kmett on Type-Class Coherence and the Orphan Rule

HN points to it as the definitive explanation of why coherence and the orphan rule matter, in debates over Haskell, Rust traits, OCaml modules and Elm.

Edward Kmett speaks at the Boston Haskell meetup about type classes and the design tradeoffs of global coherence compared with other approaches to implicit instances. It covers why uniqueness of instances matters for reasoning and refactoring.