IO then abstraction
Still, today, over 25 years after the introduction of the concept of monads to the world of functional programming, beginning functional programmers struggle to grasp the concept of monads. This struggle is exemplified by the numerous blog posts about the effort of trying to learn about monads. From our own experience we notice that even at university level, bachelor level students often struggle to comprehend monads and consistently score poorly on monad-related exam questions.
Considering that the concept of monads is not likely to disappear from the functional programming landscape any time soon, it is vital that we, as the functional programming community, somehow overcome the problems novices encounter when first studying monads.
Visual Support for Learning Monads, Tim Steenvoorden, Jurriën Stutterheim, Erik Barendsen and Rinus Plasmeijer.
...so where are students of Haskell most likely to have their first encounter with this irksome interface? Here's a hint:
IO is the monad you cannot avoid.
Why Haskell is so HARD? (And how to deal with it); Saurabh Nanda.
If bachelor-level students are often struggling to comprehend the monadic interface, then it has no place whatsoever in any introductory Haskell course! I/O in Haskell must therefore be totally independent of the monadic interface. The introduction of this interface, including its basic operations, should be deferred to an advanced course of study where it can join functors, applicatives, arrows and maybe even category theory itself: only then should students be introduced to monadic I/O.
The most difficult construct for students to understand is the monad. I introduce
IO without mentioning monads.
A simple general-purpose model of I/O for non-strict functional languages remains an open research problem...