State Monad For The Rest Of Us

Distilling the State Monad from the very ground up. In F#, no prior knowledge needed.

If you are completely new to Monads, the ticket to get you in the loop could be the gentle introduction of Monads for the Rest of Us which uses C# examples. This series, instead, uses F# and is only slightly more challenging. Nonetheless, no previous knowledge of F# is needed, neither is understanding of monads. In fact, the series starts from the scratch and builds an intuition on State Monad from the very ground up.

Important note: using a state monad is amazingly easy; building one from the scratch is a bit more challenging. Part I and II are about building it. Part III is way easier, since it is about just using an already existing implementation..

Table of chapters

Part I

In which you solve a stateful problem with pure functions.

• Chapter 1: in which you play with recursive types and recursive functions.
• Chapter 2: in which you find that binary trees have no more secrets for you.
• Chapter 3: in which you invent Functors.
• Chapter 4: in which you hit a brick wall.
• Chapter 5: in which you face an existential crossroad.
• Chapter 6: in which you discover that Procrastination® is The Functional Solution to all problems.

Part II

In which you develop the State Monad.

• Chapter 7: in which you use a bit of type modeling to hide the state handling logic.
• Chapter 8: in which you discover Applicative Functors.
• Chapter 9: in which you learn to manipulate the state like it was mutable.
• Chapter 10: a short one in which you play with signatures.
• Chapter 11: in which you finally give birth to a State Monad.
• Chapter 12: in which you see LINQ for what it is: a monadic engine.

Part III

In which you play with some State Monad use cases (and you see how easy they are)

Enjoy the journey!

References

• State Monad For The Rest Of Us - source code
• Arialdo Martini - Monads for the Rest of Us

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