In Haskell, the RIO monad
is a specialized form of ReaderT env IO, which can be used to implement
a simple but versatile effect system, where effects are available via the
environment env.
In Idris, we need an additional effect layer for error handling. This library
therefore provides a simple, stack-safe effect type, RIO e x a, where
e is the environment we need, x is the type of error our computation
can throw, and a is the result type if all goes well.
Such a type can be enhanced with several effects such as mutable state or a file system, by making the corresponding functionality available through the environment.