You've given some toy examples, but in the real world you're writing custom decoders. For example, when interoperating with any API that you didn't write. Your

You've given some toy examples, but in the real world you're writing custom decoders. For example, when interoperating with any API that you didn't write. Your example would lead us to believe that nobody is writing custom decoders in Haskell that look like Elm's decoders, and that's... very misleading.