I still find Philip Wadler’s original paper on Monads to be the clearest explanation of the pattern and concept. It remains scoped to the usefulness of the concept in programming, lays out very clear motivating examples, and proceeds to implement the pattern to solve each case in a lucid and explocit manner. I’d say the only downside is that it assumes at least some familiarity with FP and writing more “theoretical” or academic tools like evaluators, but all in all it’s still much clearer than the majority of garbled explanations of monads, even those that attempt to explain the concept through its dependencies/priors (functor/applicative).

here’s the paper: https://homepages.inf.ed.ac.uk/wadler/papers/marktoberdorf/b...