Effect systems have always felt to me like the functional programming community re-inventing dependency injection, but at the type level.
At the term level, you could just let your function have a function as a parameter `read_file: IO -> String`, vs. annotating it with some kind of type-level "filesystem effect". And the former is a lot more flexible over time.
At the term level, you could just let your function have a function as a parameter `read_file: IO -> String`, vs. annotating it with some kind of type-level "filesystem effect". And the former is a lot more flexible over time.