This is a comprehensive timeline of monad tutorials and related articles.

Please update this list as it becomes outdated! If you find a tutorial, article, post, comment, or message that stands on its own as an explanation of monads, then please take a moment to paste the link somewhere on this page (register a throwaway account, if you prefer). The date, author, and blurb can be added later. This will greatly help others who are using this list as a resource for learning about monads.

## before 2000

• 1992-02 (published date) The essence of functional programming - Philip Wadler
• 1992-08 Monads for Functional Programming (pdf) - Phil Wadler, a designer of Haskell [9100 words] . Note that this PDF seems to be from 1996, according to the TeX error on page 14. It has a reference dated 1995.
"Shall I be pure or impure?" ... "A monad is a triple (M; unit; *) consisting of a type constructor M and two operations of the given polymorphic types."
• 1995-05 Monadic IO in Haskell 1.3 - Andrew D. Gordon and Kevin Hammond
"We describe the design and use of monadic I/O in Haskell 1.3"
• 1999-02 What the hell are Monads? - Noel Winstanley [2800 words]
"Once upon a time, people wrote their Haskell programs by sequencing together operations in an ad-hoc way." ... "For our purposes, a monad is a triple of a type and then> & return operators defined over it so that the following laws apply: ..."
"...monads can be used to implement several other programming features including: consuming input, producing output, exceptions and exception handling, nondeterminisim."

## year 2002

• 2002 Yet Another Haskell Tutorial (Chapter: Monads) - Hal Daumé III
"The definition of a monad is a slightly trimmed-down version of our Computation class. The Monad class has four methods ..."

## year 2003

• 2003-08 All about Monads - Jeff Newbern [22600 words] (Japanese translation: モナドのすべて)
A comprehensive introduction. Covers monad transformers and some common monads. An appendix presents monads as assembly lines.
"A monad is a way to structure computations in terms of values and sequences of computations using those values."

## year 2004

• 2004-07 A Schemer's Introduction to Monads - Dave Herman [1700 words, Lisp, Scheme]
"The main insight of monads is that all side effects, from mutation to I/O to non-termination, have one thing in common: order of evaluation matters." ... "So monads are about talking about effects in the context of a pure semantics."
• 2004-07 Monads as Containers (Russian translation) - Cale Gibbard [2900 words]
"A monad is a container type together with a few methods defined on it. Monads model different kinds of computations." ... "it is more natural sometimes to begin with map (fmap), return and join"
• 2004-08 Monads in Perl - Greg Buchholz [2200 words, Perl]
"Essentially a monad is a hidden data structure (Fig. 1) which automatically passes state around for us. "

## year 2005

• 2005-07 Monads in Ruby - MenTaLguY
Presents monads in a friendly language, starting from Identity
"They let you chain pass [bind] operations together to make little computational pipelines, with rules of your choosing. They don’t manipulate values themselves — that’s the job of the blocks (functions) you plumb together using the monad."
• 2005-11 Of monads and space suits - Eric Kow
Functions are space stations, parameters are astronauts and monads are space suits that let us safely travel from one function to another.

## year 2006

• 2006-03 Understanding Monads - Eric Kow
Monads as nuclear waste containers, an adaptation of monads as space suits with a new metaphor suggested by Paul Johnson
"What we need is some way to capture the pattern 'do X and then do Y, where Y may be affected by X'. Monads are the way we do this." ... "In a sense, each monad is its own little minilanguage specially suited for its particular task."
• 2006-07 The Monadic Way - Andrea Rossato
A two-part tutorial. The first part shows you how build a simple evaluator, and the second part shows you how to "take the complexity" out of it by using techniques such as monad transformers
Revised 2006-09 to include Meet Bob The Monadic Lover: "what monads look like and what they are useful for, from the perspective of a ... lover."
• 2006-08 You could have invented monads! (and maybe you already have) - Dan Piponi
"Writing introductions to monads seems to have developed into an industry," Dan (sigfpe) observes. He argues that monads are not "something esoteric in need of explanation", but walks you through the process of reinventing monads to solve some very basic and practical problems.
"So now I can reveal what a monad is. The triple of objects (m,unit,bind) is the monad, and to be a monad they must satisfy a bunch of laws such as the ones you've been proving."
"I think of monads as computational environments in which you get to make up the rules." ... "monads are ... a general model of computation that lets you pick and choose the environmental features that you want for your computations."
• 2006-10 Monad Transformers Step by Step - Martin Grabmüller
Monad transformers are rarely covered in introductory tutorials. This "is not a paper about implementing transformers, but about using them to write elegant, clean and powerful programs in Haskell". Available as a 12 page PDF or .lhs file.
• 2006-11 There's a Monster in my Haskell! Andrew Pimlott
This delightful "tutorial" presents monads as monsters which devour values, use them to feed other monsters and regurgitate them when slain.

## year 2007

• 2007-01 Think of a monad - Don Stewart (reposted on Eric Kow's blog)
Don integrates some pre-existing monadic metaphors, shedding light on monads in a truly comprehensive manner (illustration by Eric)
Author's Description: This crash course starts with an EASY! introduction to categories and functors, then we define a monad, then give some basic examples of monads in categories, then present monadic terminology as used in programming languages.
• 2007-03 Monads in 15 Minutes - Eric Kidd
Eric boils monads down to 15 minutes, using backtracking and Maybe as motivating examples. Eric uses `join`, which seems quite rare for monad tutorials (cf Cale's Monads as containers)
Then I lie down in a dark room with a warm wet cloth over my eyes.
• 2007-08 Monads as computation - Cale Gibbard
A very straightforward presentation of monads. Notable for its "The whole point" section, which conveys why we bother with all this monad business.
• 2007-08 Understanding Monads (2) - Apfelmus
Wikibook rewrite of the original monads tutorial. Less fluff, more pedagogy. [In progress at the time of this writing].
• 2007-08 Monad (sans metaphors) - Claus Reinke

## year 2008

• 2008-01 An explanation by 808140 [1588 words]
"The best way to grok monads is to ... familiarize yourself with several common monads and their uses." ... "All that makes a monad, really, is that you can define two functions like unit and bind on them."
• 2008-03 Real World Haskell, Chapter 14: Monads - Bryan O'Sullivan, Don Stewart, and John Goerzen
"We aim to show you that a monad is often an obvious and useful tool to help solve a problem."
• 2008-06 Monads (in Russian, English translation) - Eugene Kirpichov [8200 words ru, 10000 en]
"A monad is a triple (m, return, >>=), where: ..." ... "As we progressed, we saw that monads are most commonly used for two different purposes: structuring the control flow and describing imperative effectful computations (IO, State, IndentIO), and structuring data flow (Maybe, List, Dist)."
"An alternative term is computation builder which is a bit more descriptive of what they are actually useful for." ... "In layman's terms, a monad is just a type for which the >>= operation is defined."

## year 2009

• 2009-01 Abstraction, intuition, and the “monad tutorial fallacy” - Brent Yorgey [meta]
Commentary on monad tutorials and why many may be so unhelpful. "What I term the 'monad tutorial fallacy,' then, consists in failing to recognize the critical role that struggling through fundamental details plays in the building of intuition."
• 2009-03 How you should(n’t) use Monad - beelsebob
"When we have functions that produce values that are hidden inside boxes, we have a problem. ... Monads add a single function called join, which is used to flatten out the layers of boxes: ..."
• 2009-06 The Greenhorn's Guide to becoming a Monad Cowboy - Hans van Thiel [9600 words]
Covers basics, with simple examples, in a for dummies style. Includes monad transformers and monadic functions. "Actually, programming monads is much like cattle driving! So, let's get started."
• 2009-10 The State Monad: A Tutorial for the Confused? - Brandon Simmons
This is written for someone who has a good understanding of the Maybe and List monads, but has gotten stuck trying to understand State... State monad is just an abstraction for a function that takes a state and returns an intermediate value and some new state value.
• 2009-11 What a Monad is not
A desperate (futile?) attempt to end the eternal chain of monad tutorials.

## year 2010

• 2010-03 State Monad Tutorial - Byron Johnson
"My goal is to teach others to help them understand the State monad. ... After this point, you should be able to easily understand the other monads."
• 2010-07 I come from Java and want to know what monads are in Haskell - Tim Carstens [Java]
Translates a simple Java class into a stack of monad transformers, with a metaphor about how monads are like conversations, and why this idea should be familiar to OO programmers.
"What I am going to talk about is how to use monads to do something in Haskell that is easy to do in Java." ... "This is what different monads do: each comes with its own set of operations that are legal within the context that the monad is modeling."
• 2010-08 Yet Another Monad Tutorial, part 1 (2, 3, 4, 5, 6, 7, 8) - Mike Vanier [7100 words p1, 45000 total]
"Monads are a generalization of functions, function application, and function composition to allow them to deal with richer notions of computation than standard functions."

## year 2011

• 2011-01 Monads for the Curious Programmer: Part 1, Part 2, Part 3, and Monads in C++ - Bartosz Milewski [3400, 4300, 3400, and 5200 words]
"Monads are hard to describe because they don’t correspond to anything in our everyday experience" ... "A monad is an endofunctor together with two special families of morphisms, both going vertically, one up and one down"
"A monad is a wrapper type around another type (the inner type), which adds a certain structure to the inner type and allows you to combine computations of the inner type in a certain way."

## year 2012

• 2012-04 Why Do Monads Matter? - Chris Smith
"... The category that they form is called a Kleisli category, and it’s basically another way of looking at monads."
• 2012-08 Monads in Pictures - johnw
"This is not a tutoral on monads, nor will I use any math terms here. This is for people who have learned enough about monads to use them, but want to get a better picture of what they’re doing and why they exist."
• 2012-11 Monads à la Mode - Cameron Swords and Daniel P. Friedman

## year 2017

• 2017-11 Learning Monads by Example - Diego Vicente
"While writing my bachelor thesis, a heuristic search framework in Haskell, I ran into a roadblock I long feared to have: I needed to understand how monads work."