The Absolute Best Intro to Monads For Software Engineers

If you had to pick the most inaccessible terms in all of software engineering, monad would be a strong contender for first place, because of its spooky math background that uses terms like endofunctor and monoid. As it turns out, monads are an extremely powerful design pattern that can be used without any math knowledge. In this video, we’ll cover what monads are, how they can be incredibly useful, and examine some common monads. All you need is a little software engineering knowledge. Let's go!
Dr. Strange Icon Credit: dribbble.com/dalius-stuoka
00:00 Intro
00:29 Basic Code
01:45 Issue #1
02:38 Issue #2
04:11 Putting It All Together
05:15 Properties of Monads
06:05 The Option Monad
09:14 Monads Hide Work Behind The Scenes
11:21 Common Monads
12:10 The List Monad
13:56 Recap

[@asadsalehumar1011]

Hands down the most awesome explanation of Monads on KZbin

[@neogen23]

My experience as well, though I realise as much having already understood the concept via classic methods (see a book on Haskell), so I was like "Yep, that's totally it". I doubt it would have helped me if I had used it as tutorial material. Still, a stellar explanation

[@AutoFirePad]

It turns out that we have been using monads without even knowing it for years.XD

[@erikkostic8271]

Feel you

[@stopper0203]

Agree

[@quantisedspace7047]

Maybe it was. I gave up when I heard the stupid music.

[@jcolt452]

How on earth did you break the curse!? .... "Once you understand Monads you lose the ability to explain them"! 🤣

[@aiocafea]

you have to trick a veteran functional programmer into helping you if you start explaining monads to enough people that already understand them, eventually one will tell you 'oh you don't _actually really_ understand monads unless you understand…' and suddenly you will feel this clearness in your brain you can suddenly explain this concept and all of the useful ramifications

[@Bergerons_Review]

I think that's true for most coding problems ;)

[@GesteromTV]

This is greate video that explain how to use monads and how fo recognize them, but in true math style there is whole universe that you skiped.

[@ArturCzajka]

@@GesteromTVAnd that's how he shoved it into a 15-minute video, and not a 60-minute lecture 😝

[@Lee-qj4hk]

Monads are a brain virus which makes you believe in Monads

[@gargshishir3]

After maybe 10 years of periodically going back to the definition of monads, googling and still not understanding what the hell they are, you have done it! Thank you, one less mystery in life.

[@KingTheRat]

I watched this video last year, and this year, I already do not remember what it is. Time to watch this video again. :)

[@gargshishir3]

@@KingTheRat I did that recently too 😆

[@scheimong]

That was fun to watch. I've been writing rust for a good while now, so basically I've been using monads everyday all this time without knowing the concept's technical name. Watching you refactor bad typescript step by step into rust felt funny.

[@ChrisD__]

And this explains why don't understand Rust... I didn't understand monads!

[@nobodyinparticular8219]

Very good explanation, finally someone who's using a programming language which people who don't yet know what monads are can actually understand. Another good video on the subject is Brian Beckman's "Don't fear the Monad" which explains it in a more abstract way, but still using familiar terms. Other videos, and especially Computerphile's video were completely inaccessible to me and left me thinking that I'd need to spend months studying category theory or at least read a book on Haskell before I could understand this concept. You and Brian made me realize that I had actually invented monads on my own and have been using them without knowing what they are.

[@evanroderick91]

I'm not familiar with this programming language. What language is this?

[@rakandhiyaaa92]

@@evanroderick91 I think this is typescript

[@younes3573]

@@evanroderick91 as mentioned before it is TypeScript: JavaScript but with types

[@denisg1208]

I agree with you about video ‚Dont fear the monad’. Also explains it really well

[@MrRedstonefreedom]

It's funny you mentioned the computerphile video because I likewise, even in using monads wherever applicable, watched that video and felt like I understood it even less. Even funnier still is the disclaimer he gave of "well people criticize mathematicians for not being able to explain their concepts in relatable terms, but I think they should just get over it". And it's like... they will get over it, by just ignoring their work & having to rediscover it anyways in their own contexts.

[@connorkapooh2002]

Dude. This was fucking sick, please keep producing videos like this. I think there's also a lack of beautiful visualisations for more advanced concepts (which makes sense because more people are going to be beginners). Keep it up man, your animations are absolutely gorgeous :)

[@chachan4142]

Thank you. this video is very practical, informative, and truly demonstrates what can be achieved with monad with actual example and not just the abstract concepts of it all. Best one yet that I've seen on KZbin. You've earned a new. subscriber!

[@JoshuaKisb]

first video that actually explains monads in sensible approachable way. thank u very much

[@youngcitybandit]

This seems like a very intuitive pattern but at the same time I never knew this could be so formalized. Thank you I learned a lot

[@brettm4179]

I loved this video. Would love to see some explanations on applicatives and functors as well and some fp-ts examples. The pipe and flow makes using monads and functors so nice

[@CFEF44AB1399978B0011]

I'm blind and you were able to describe your content without using this and that while pointing at places in the code. nice work.

[@steveloco1170]

bro WDYM YOU ARE BLIND AND WATCHING KZbin

[@CFEF44AB1399978B0011]

@@steveloco1170 you do realize blind people live normal lives?

[@jhoughjr1]

@@steveloco1170 main thing to know is "blind" is shorthand for visually impaired. Also you can learn from hearing too.

[@GVSM-xo9ri]

By far the most amazing explanation i've ever read. Nice examples, made the concept a lot easier to understand!

[@arongil]

+1, this video taught me exactly what monads are from a practical standpoint. Thank you!

[@romanmahotskyi6898]

This is one of the best explanations I've ever seen. Thanks a lot

[@MrRedstonefreedom]

Jesus, this is such a robust explanation. This could be watched every 3 months just to reconsider newly-encountered applicability. I already came to the same conclusions about monads in programming (as a design pattern, in any kind of paradigm or language), and done a lot of deep thinking, but even still, this is such a wildly useful video as a consolidation tool. You've given a lot of excellent visualizations that make aspects-management & its expression a lot easier.

[@papetoast]

As someone who didn't know monads, this is an excellent video! You started with an iterative approach on simple examples to give an intuition of why the idea of monads is useful. Then after having the intuition you give a more abstract, rigorous definition, along with real usages. I think I wouldnt have been able to understand the abstraction as easily if there wasnt the simple examples in the beginning. Then you give a summary to help remember the content of this video. Overall I think the flow is great and the pace is just right. Sometimes I have to pause a bit to understand the code but I never have to think really hard to understand since the leaps in logic are always small enough. Thank you for making this video!

[@vikingthedude]

This is some good stuff. I'm also glad to see you have other videos. Hoping you get more subscribers, you deserve it

[@erikgrundy]

I've always thought that the definitions people used are always more complex than they need to be. I'm glad you've managed to explain it in a way that feels like something a programmer would do

[@user-tx4wj7qk4t]

By programmer you mean code 🐒

[@erikgrundy]

@@user-tx4wj7qk4t i don't, and i'm a little confused at what you're implying. do you mean that no "real" programmer requires it to be explained like this? or that you don't think the code in the video is very good? please, enlighten me

[@user-tx4wj7qk4t]

@@erikgrundy a software engineer is supposed to be an engineer. An engineer uses math and science to solve real life problems. However "software engineers" are the only kind of engineers who hate math and science and think even simple basic math is "too complex" and are always looking for immediate answers on "how" to use something, with very little understanding of "what" something is or "why" it is. The explanation above is terrible for very many reasons but mainly because he doesn't actually explain anything any what a monad actually is, it's just overly convoluted examples of what you can do with it which ironically is more complex than if somebody just explained what it is. You saying "feels like something a programmer would do" means code monkey because actual software engineers understand math and don't explain things this way

[@MadaxeMunkeee]

This video is a true triumph. Thanks so much for making it!

[@JamesWalker-rs1ps]

Hey, this is great! You've got a good way of explaining things using plain English and building concepts from a basic level.

[@blakedowling7002]

Amazing work here. Turns out I've been partially harnessing the power of monads the whole time, but understanding how you can simply chain passed functions brings my software engineering understanding to a new level. Thanks for your effort in making this video Alex.

[@Masto12321]

You won yourself a subscriber with this clean clean video. Can't wait to go through more of your content!

[@atrowell]

Impressive explanation. Quickly provided useful information that gives me better understanding of techniques I already use as well as new ones to adopt.

[@therealguanzo]

One of the best videos on programming I've ever seen. Subscribed. Please make more!

[@dcuccia]

I mean, "Its just a monoid in the category of endofunctors. What's the problem?" Scott Wlaschin also does a great job of explaining monads graphically with his "Railway Oriented Programming" talks. But this was a great "part to whole" way to take a single use case and expand the concepts, step by step. Nicely done!

[@prince_of_devils]

Definitely lives up to the title, thank you for making such a great explanation.

[@sgwong513]

wow, first time I know monad so clearly. thanks and looking for future video like this. really good video.

[@sct848]

Please keep coming up with great content like this, thank you!

[@eliote.corleyii5792]

I only wish I could like the video as many times as I have watched it. What an incredible presentation and a simple explanation of such a feared topic. Thank you.

[@karavind7814]

This is the best video explaining monads, thank you for the great yet simple explanation 😊

[@yellingintothewind]

I think a large part of the issue explaining Monads is the concept is actually so simple that there is a "why the special name?" question that makes people think it _must_ be more complex. It is a basic function-application pattern, the likes of which you learn the first time you write an async event loop, or implement a DSL-FSM (See Greenspun's 10th rule). And yes, just like the y-combinator, or lambda calculus, it has a basis and explaination in math that makes it look more complex than it really is.

[@user-tx4wj7qk4t]

None of what you said is true

[@aoeu256]

In Javascript Promises/Futures are an example of a Monad, and in that case then is flatMap/ >>=. However, Monads generalize the idea of promises/futures to be able to embed any language with any sort-of semantics into the language, so promises/futures are a way of embedding asynchronous computing into a stateful language and have it look like synchronous code just like monads are used to embed imperative/stateful languages into purely function Haskell. The thing about monads is that you have to know their 5 other definitions and many other examples to see how monads can shorten your code by. You have to know Monads other definition like flatMappables containers where flattenable containers are called Monoids, Mappables are called Functors.

[@julestburt]

I founded Vancouver's Functional Meetup which ran for 3 years...and we discussed monads a lot!! I had a lot of ongoing questions. I saw many presentations, yet I was always left wondering / wishing someone could actually show me a 'monad' rather than discussing the apparent philosophy or upper purpose! Finally, someone explained it with great code examples, which I could easily relate to Swift (my language) and completely and finally understand monads...I had assumed one didn't really need to know 'monads' to use them, and it turns out with arrays, maps/flatmaps, optionals, and even a plug in Then promise library - all these were monads of course and I didn't need to know one to use one...but your explanation nails it! Many thanks!!

[@wcarmon1209]

You have quite a gift for education. Thanks for taking time to explain this.

[@hansschenker]

Practical samples and very good explanations! Thank's for publishing!

[@ocnah]

Absolutely greatly presented and explained, well done.

[@TheJonBrant]

Incredible video. I felt a lot of clicks, and feel like I may have understood monads better than I thought. Thank you!

[@ryannygard3661]

I just made a monad this week without even realizing it, but I never thought about implement logging into it. I'll need to do that immediately because that would be extremely useful!

[@yeong126]

Among all the functional programming videos in my feed this is the first one I understand something. Great video!

[@ShykinArcana]

I've been doing this for years and just calling it good encapsulation and treating functions as a blackbox. Reduce how much the caller needs to know about the function and allow it to be a blackbox. Or rather I suppose, how to create the blackbox in the first place. Good to know the new vocab for it and this is a really good explanation, much better than I could give to new devs. I'd frankly send them to this video to learn the concept.

[@denisg1208]

The way I understood it, monads require a logging of sorts no? Or was that just one use case for monad patterns

[@denisg1208]

Nevermind it was just an example.

[@user-tx4wj7qk4t]

You've got no idea what you're saying and just saying things lol

[@mabuelhagag]

I recently discovered Effect-ts and was struggling to understand the basic concepts of it. The docs don't mention mondas while explaining how the library works (due to a valid reason. Mentioning monads scares people!) But this video explains it beautifully! Thank you man! You got yourself a subscriber 😊

[@aryanrahman3212]

Thank you so much for such a simple but relevant explanation!

[@Aucacoyan]

This is actually great teaching material, thank you so much!

[@rajthewise]

This is the first video that 'shows' the thing by including 'how to' aspect. Best video I came across so far.

[@ZackFreedman]

Great explanation. I'm going to use this as a benchmark when I do actual education videos.

[@crckrbrrs]

yeah, now that i think about it the oscilloscope video was quite similar to this one

[@abdulhamidalsalman]

Alex you are the champion of the web. You deserve a noble prize for making these great videos.

[@tqian86]

This is an amazing intro in the sense that the title isn't even a clickbait! ;) Thanks for the video!

[@Sahuagin]

this is the best explanation of monads I've ever seen, thanks

[@CartoType]

Very interesting and new to me. One small thing; what you call a caret, < or >, is more properly known as an angle bracket when it is used as a delimiter. This is a caret: ^.

[@NicholasShanks]

Yes, worst part(s) of the video, that.

[@jasonzuvela]

Exactly! So painful to hear every time. en.m.wikipedia.org/wiki/List_of_typographical_symbols_and_punctuation_marks

[@31redorange08]

That's a circumflex.

[@jamesmstern]

This is a marvel of clarity.

[@brettwines6812]

can confirm, is the best introduction!! Honestly so so good

[@aysubetin-can6435]

At last! Great video thank you so much!Great namings, wrapper instead of unit and run instead of flatmap or bind to explain the concept before the terminology. Please make more videos like this

[@Seyunx]

Topo keep up the amazing work, you deserve more views!

[@darkarie]

really well explained. I subscribed in the middle of the video, keep it up!

[@kellybmackenzie]

4:43 Thank you SO MUCH, seriously! When you said that it instantly clicked. This genuinely helped me so much, thank you!

[@ohm62]

Stellar presentation of monads! Thank you so much!

[@n4vyblueyes377]

Thanks for putting this together. Obviously took some time and it is a dry topic. Much appreciated. 👍

[@SteveDellaValentina]

I'm not sure how I stumbled on to here but I'm glad I did. This is not only helpful as a software engineer, but a really good example of how to teach an abstract concept in a very accessible way. Very nicely done, and subbed!

[@dawid_dahl]

One thing I’ve noticed that is tricky is when you have a value wrapped in several monads. For example, if you have a value that is asynchronous and also can fail with an error. Then you have a value wrapped in a Future/Promise/Task as well as an Either. Would love a video about how to deal with this complexity. How to traverse between different monad lands.

[@Holobrine]

You’d probably pass one “runWithLogs()” into another, nesting the functions in the same way the types are nested

[@ivanjermakov]

Yep, because Promise.then() has the same type signature and meaning as flatMap (or bind in monad). It transforms promise, using a function transforming wrapped value into a new promise.

[@HolyAvgr]

​@@ivanjermakov wouldn't this be trivially solved by back-tracking the function through the unwrap, since both monads are Generic in their implementation? If you have a Future, what you probably have is something in the form of future(optional(5)), which can also be expressed as a chain operation as: let result: Promise = createOptional(5) | .createFuture($0) in which case you should probably be able to do something like `result.value.value` which should resolve without much problem: Unfulfilled promise would nil .none in the optional would also nil

[@ArturCzajka]

Keywords are: monad transformers (more popular, safer to start with this) and extensible-effects (imho cooler) 😄

[@jn-iy3pz]

I watched a few videos but this is the one that made sense to me. Thank you!

[@semplar2007]

very well put together explanation 👏

[@jongeduard]

Thank you for this extensive explanation! 👍It's really useful as a background knowledge behind a ton of things in Rust that I learned, also because I have seen many people already talking about it there. Now I really understand it. 👏 But even in C#, a language in which I have worked for about 20 years now, I can relate several examples of monads as well. A nice one are so called LINQ functions, for example SelectMany, which is basically the literal equivalent of your FlatMap example. LINQ is the name of the most important functional programming API in C# and DotNet. Maybe it is also a good to mention that C# was really one of the first with the async await programming model, and it might even be the absolute first one. Though what you mentioned as Future or Promise are not the terms how they are used in C#, but what is used is generally Task or ValueTask, although other types can also be used sometimes.

[@d0m186]

Best video i have seen on this topic. Most videos start with explaining monads, monoids, and endofunctors and are completely overcomplicated. Starting with an easy to grasp example is way better

[@atanugayen3030]

I kept seeing this video recommended to me, but I avoided it everytime thinking "this is gonna be too complicated, I'll watch it later when I have the time/energy." Glad I finally bit the bullet and watched it... was not disappointed. Fantastic explanation... please keep making videos like this!

[@ya3rub101]

best monads explanation i've ever seen !, thank you !!!

[@Daspem25]

Dude your channel is a gold mine!!

[@grkuntzmd]

Best explanation of monads that I have seen. Bravo!

[@Mrhennayo]

Simply simple explanation sire !

[@avi3681]

Great to see the clear examples in TypeScript!

[@gavintillman1884]

I’ve been struggling with the concept and think this may be the best presentation I have seen.

[@sergeiknyazev5564]

Great explanation! Would love to see free monads as I'm struggling with those myself.

[@atalhlla]

You got me, I was about to freak out about you not mentioning Lists/Arrays. Very good explanation and examples!

[@SaySaeqo]

That was seriouesly the absolute best intro to monads, thanks

[@Daniel_WR_Hart]

I watched a bunch of talks about what monads were, but this was the first to make me realize that I actually wrote one unintentionally last year while trying to learn about design patterns

[@jaybny]

best thing I've watched in years! awesome job 👍👌👍👌👍

[@aj.arunkumar]

very nice one.. thanks for making this

[@endermannull4420]

I first grasped monads by thinking of them as piggybanks. The ceramic ones that you have to break. This perfectly compliments that, thank you!

[@marcelo6279]

Amazing explanation!

[@jeffg4686]

very helpful. Perhaps the only place that gave me a better grasp of monads

[@Irokesengranate]

This was extremely helpful, thank you!

[@denys-p]

Just for reference, in C# flatMap for lists (actually, all collections that provide IEnumerble interface) is SelectMany in Linq. Future/Promise is the Task. One more interesting thing - async/await (combined with Task) is very close by it’s behavior and purpose to IO monad (not mentioned here) - it “infects” function so you need to make functions that call it async (or, at least, return Task) as well. And it brings a big mindset shift, starts building understanding that we want to keep “IO monad” part as small as possible, splitting logic and IO. It will allow to write most of tests without mocks at all. And the rest that works with “outer world” (db, user input, other services calls etc) better to test with real interaction, e.g. integration tests.

[@MrRedstonefreedom]

The second part you wrote is potentially a good point, but I'm not convinced it's true. I know exactly what you mean by "infection" (I call it "prionic", and if someone doesn't know what a prion is, I go for ice-9 if they've ever read Vonnegut). But, I'm not sure it's really possible to have async in any kind of way where it doesn't "infect" all of its uppers. Actually, callbacks in JS would possibly do this. But that's more a matter of using global state. Although, additionally, mutex's in general work this way. Thinking of reentrance patterns and such. Ok, you've convinced me. Yea I think this is a unique quality for Task. Even deeper, I think this may be a unique quality for Monads, overall. An accessory requirement for that to be the case is BTW this is somewhat similar to the mathematical concept of "absorbing elements". I think Undefined, though, would most-closely mimic the concept of a synthetic (ie intentional union with) construction of a category with an absorbing element.

[@MrRedstonefreedom]

**An accessory requirement for that to be the case MIGHT be that it's a typed language. Though I think that's just a straight matter of "in order to be less immediately annoyed of categorically wrong implementations"

[@KaiHenningsen]

@@MrRedstonefreedom Typescript (in the video) gets compiled into normal Javascript, mostly by stripping away the types. So the async/Promise stuff usually becomes the exact same operations in Javascript. For that matter, the node.js runtime has a utility function util.promisify() that converts a callback-using function into a Promise-using functions, and Promises have .then, .catch, .finally etc that resolve Promises with callbacks. The two are essentially equivalent.

[@C00l-Game-Dev]

A fellow c# bro.

[@_blank_3677]

Dude… years… years I tell you!!!! Why does everyone else suck sooooo bad at explaining this! Finally! I feel complete. Ty

[@Goras147]

I guess it's really as simple as that huh. I always heard monads are the bane of one's existence, but this seems rather beautiful and understandable. Grat video!

[@o__sama]

Amazing explanation, thanks !

[@OroborOSX11]

The fact that Swift has built in operator support for optionals using ? is so nice. It’s nice to be able to wrap up this behavior into a simple type declaration like User? (equivalent to Optional).

[@yahyaadinugraha1058]

dart as well

[@user-tx4wj7qk4t]

It's not equivalent

[@peteryuen4481]

The clearest explanation that I have seen👍👍👍

[@kingshukmajumder2087]

One of the best descriptions of monad!

[@quinn_m]

Big fat subscribe for this, made it so clear and gave great examples; thank you Alex

[@danilmartyniuk]

great explanation. I will definitely use monads in my projects.

[@tenoeg]

Man, you make Monad fun to watch!

[@Radioguy00]

Excellent delivery of information

[@eltongarcia6105]

Outstanding work! thank you so much.

[@Psychx_]

So this is why Rust has std::option and encourages the use of some/none. Very informative. TYVM!

[@kirillnovik8661]

Now we need a video, where we have side by side implementation of monads in Haskell and TypeScript

[@pedroth3]

Indeed a great monad intro

[@ivanjermakov]

13:30 It's called flatMap not only for lists, but for any type that introduces structure. More generally, it's called bind or concatMap, it has a type signature of (struct: Struct, transform: (value: T) => Struct) => Struct, and means "Map a function over structure and concatenate the resulting structures". It is possible, because any monad must also be a monoid: define how to combine structures. Basically, monad is a very general interface for flatMap.

[@calico2808]

this is very clear thanks!

[@camilosibarita]

Thanks for the brilliant video!

[@Ratchet813]

Woah, I hadn't known before that Futures & Promises are monads too. Nice video man!

[@roelofhoeksema4657]

I wish i could like this video every time I come back to it.. So well explained :D

[@edgeeffect]

I had never really studied monads, mostly because of "that stupid quote" - you know the one I mean. Then, I can't remember why now, I was looking at a promise one day and thought "could this be a monad?" I'm now looking for a way to explain to bosses why async/await isn't necessarily a good idea and why promises are actually much clearer. But bosses often want a "clever" explanation that's hard to understand so I've been thinking about invoking monads in my overcomplicated explanation... and here we come full circle because "deliberately overcomplicated" and "that stupid quote" are the very best of friends.