A Monads Approach for Beginners, in Scala | Rock the JVM

[@politrons]

One of the best Monad laws I've ever seen. Very nice man!

[@rockthejvm]

Thanks!

[@ketanpurohit9086]

I have read articles and books, cried tears of blood while going thru them. And then I find this.. Wow -- well done. If your courses are like this.. I am a buyer for sure. Keep up the excellent work.

[@rockthejvm]

Such awesome praise, thanks! I have lots of content like this on the site.

[@rohanurkude8503]

Bravo!!! There are no bad students , just incompetent teachers. I am proud to say I CAME ACROSS THE BEST TEACHER!!! Kudos to you Daniel :)

[@rockthejvm]

Such high praise, thanks!

[@michaelreuter5403]

Absolutely best description/explanation I have seen! It "clicked"

[@rockthejvm]

Great to hear!

[@ernestbednarczyk5745]

You've got talent for keeping watcher's attention through whole 40min video :) Thanks for great content!

[@rockthejvm]

Thanks - glad it's useful!

[@daqo98]

Such a brilliant explanation. Thank you very much!

[@sagnikbhattacharya1202]

This video FINALLY made me understand HOW to use monads!

[@rockthejvm]

That's my goal!

[@slim_mike]

I liked very much that you skipped the theory and stick to the behavior of the code, you can always read more about the theory if you want but explanations like this with demostration on the the terminal, I think is what is most valuable for this video. Keep up the good work! and thank you very much!

[@ivanvelikanova9950]

I am so happy I went through this video. 40 mins felt a bit too much, but I guess it was required to understand. Thanks a lot.

[@rockthejvm]

Glad it was useful!

[@LucaSavoja]

Thanks Daniel, really appreciate, I'm studying Cats right now but this video was very clear and helpful!

[@rmiliming]

Very clearly explained. The examples used are good for helping me understand the concept. Thank you very much!

[@valcron-1000]

Great video explaining a topic that often gets beginners confused. I would add that most developers have used monads in some way without knowing the underlying concept: - async/await especial syntax is kind of the same as 'for comprehension' but specialized for async code. Instead of using 'await' you use '

[@rockthejvm]

Well said!

[@tungtranvan1286]

The first time I watch the video, I still didn't understand Monads. But, in the second, I got it. Thank you!

[@rockthejvm]

Glad it clicked!

[@2kawaii2care]

I really learned a lot from this vid! Thanks! I’m not a Scala dev but I think I can use that new flatMap approach when working with Stream API from Java 8!

[@rockthejvm]

Amazing, that's my goal for these videos - transferrable skills!

[@sherwin96]

Was waiting for such a Video. I loved the explanation at the end for the monadic laws and it did help a lot by giving concrete examples. Something that can be added as an extra to your advanced scala course. Great Video as always !! :)

[@rockthejvm]

Glad you liked it!

[@omkarkulkarni9202]

Dude, you should really have some commercial videos made! You are the best :)

[@rockthejvm]

Thanks! Check out the Rock the JVM website, I have full-blown courses on a ton of stuff.

[@dedpihter5870]

I've heard that Monad has one more property - anyone who got understanding Monad immediately looses ability to explain it to other people. You proved it's not true. Thank you for the fantastic Monad explanation!

[@rockthejvm]

Thanks!!

[@paveltroev8221]

done lots of haskell a while back but never heard of the 'm-word', gonna embrace it :-)

[@ebuzertahakanat]

14:21 you didn't mention not returning null which cause esoteric null pointer exceptions which is another benefit of option

[@ggsgetafaf1167]

thank you, I read cats book, too hard to understand, but I got all after watching your video.

[@cgmds1973]

Thank you for the video, I really like the examples !

[@seanhdr4k629]

Thank you for this wonderful video as well. I always press 'like' button. From my understanding, I presume 'for-comprehension' for List(1,2,3) and List('a', 'b', 'c') would yield a cartesian product..

[@rockthejvm]

Thank you! Yes, that's true.

[@VRMediaI]

Excellent video, sad that so few people have seen it.

[@mehow.]

scala 'for' reminds me of do/return from haskell

[@mourikogoro9709]

(8:57) line 12-13 the function actually does synchronized twice, Is that necessary for the purpose?

[@mourikogoro9709]

Can I write this instead? def flatMap[S] (transformer: T => S): SafeValue[S] = { SafeValue(transformer(internalValue)) }

[@rockthejvm]

@@mourikogoro9709 there is no double locking in this example. What you're suggesting is a map function (not flatMap).

[@mourikogoro9709]

@@rockthejvm Am I really misunderstand? Why? 1st synchronized is during apply the function's argument (i.e. transformer: T => SafeValue[S]) 2nd is the synchronized block of the flatMap function itself

[@rockthejvm]

@@mourikogoro9709 the transformer argument is a function value which can be anything; it has nothing to do with the transform method of the previous SafeValue implementation

[@biniamgebregergs4282]

Amazing video. Thanks a lot.

[@dangalimov7435]

Really useful video!

[@weissmannrob]

Very well done 👍

[@k.l7111]

At 31:02 you mentioned ‘Monad(x).flatMap(f) == f(x)’ , I am afraid this is not always right. If we try: ‘def createVector(x:Int) = Vector(x, x+1) ; List(3).flatMap(createVector) ‘ the result should be ‘List(3, 4)’ but according to your formula it would be ‘createVector(3, 4)’ i.e. ‘Vector(3, 4)’ The correct explanation can be ‘Monad(x).flatMap(f) == Monad(x).map(f).flatten’ which one can consider as ‘Monad( f(x).flatten )’ . Think of it as just flattening the inside structures. Hope this is helpful. Thank you for the great video.

[@rockthejvm]

You're mixing lists with vectors, which are obviously different things. Even so, the returned type is still a supertype of both, which still satisfies the law. The monad laws as I stated them in the video are still true for functions returning lists.

[@colin398]

Why flatMap which makes us transform the thing into a SafeValue again? Why not use map, so we dont have to write the "wrap" step in our transformation function?

[@rockthejvm]

flatMap is useful when all you have is functions returning SafeValues - if you simply map the transformations, you'll get a SafeValue[SafeValue[...]], which is not what you want

[@colin398]

@@rockthejvm Ohh okay, I was thinking maybe there was a way to avoid those nested Monads without using flatMap. But I guess not. Thanks for the awesome content

[@ZoYaBoBo]

God explanation, thank you man now i understand that sh`t !!! You have really awesome teach skill !!!

[@gastonfernandorosso4226]

Isn't the prop 2) a special case of prop 1) when f = x => Monad(x) ?

[@d4devotion]

Sorry I forgot, why you keep on saying never use Double for money in app, can you please elaborate this ?

[@rockthejvm]

Doubles can't represent tens and hundredths with full precision, which means you can lose cents on every operation. Use decimals instead.

[@d4devotion]

@@rockthejvm Is there any blog you have written around it ?

[@SanjaySinghaniaIN]

Increment the font size please!

[@dmitrydidi]

great explanation! thanks man!

[@rockthejvm]

Glad it helped!

[@chriseteka]

Thank you for the video daniel.

[@kaktusdono]

I have an issue with the first monad rule, at least as it was described here. Is it correct to assume, that in the formula: ```Monad(x) .flatMap(f) == f(x)``` the function is not just a function, but a function that can returns a Monad of the same type, and can be described as ```f[T](x: T): Monad[T]``` Am I correct to assume that? I can see that it's true for lists, but I am not sure whether it's true in general terms. Because *Option(12).flatMap(_ * 2)* is not equal to 12 * 2, it is *Option(12 * 2)* UPD: same goes for the third rule. I guess we cannot just apply flatmap to the result of *f(x)* if it is not a monad itself.

[@rockthejvm]

Your counterexamples are improperly typed - you can't say Option(12).flatMap(_ * 2), but rather Option(12).flatMap(Some(_ * 2)), in which case the law holds. Same for the third law. It's not that you can assume f to be of type T => Monad[T], but you MUST assume that by the type signature of flatMap.

[@kaktusdono]

@@rockthejvm thank you!

[@jamesking2172]

Please do an explanation of tagless final 👍

[@LucaSavoja]

oh that's would be great!

[@kmac499]

Dear God, can someone anyone please just tell me what a monad is,,, i can describe a data type, a parameter, an array, a procedure, a function, an object, recursion construcrors etc by simple analogy....but monads always instantly descend into novel and hence impenetrable jargon,,,,

[@LuizRobertoFreitas]

Monster!!! Thank u man

[@rockthejvm]

Glad it clicked!

[@theanigos]

Weekends are good learning scala.

[@rockthejvm]

I know, right? :D

[@badwolf8112]

thank you. p.s. would be nice if the text font size was extremely larger.

[@rockthejvm]

Got it - are you watching the videos on mobile?

[@badwolf8112]

@@rockthejvm no. im used to not having to go to fullscreen/look fairly close. "programming in mosh" on youtube usually has text size bigger than one would code with but I think it benefits not only mobile, but on pc is also window mode more readable than smaller font looks in fullscreen.

[@Code4Life]

Can u upload more video about implicit ?

[@Code4Life]

And some functional topic like fold, foldLeft and foldRight

[@sherwin96]

He has a course on all of that on Udemy :)

[@Code4Life]

@@sherwin96 I have learned that but feel not enough :# at advanced scala course :V

[@sherwin96]

@@Code4Life if you haven't done the Coursera scala specialization,, that is something I would suggest you look into. It really dives deep when you talk about those functions. It also covers implicit's in its entirety. You won't get anything better, especially if you solve the assignments.

[@jamesking2172]

Love it 👍

[@waagnermann]

At 30:22 you enumerate Option, Try, Future, List as Monads but Future actually is NOT a monad!!!

[@rockthejvm]

There's this age-old discussion whether a Future is a monad or not, since it includes the passage of time. For beginners (which is the scope of this video), we'll just consider Future to be a monad.

[@vijayvaswani9717]

you are awesome..!

[@DiegoFerreiradaSilva]

amazing video, thanks

[@rockthejvm]

Glad you liked it!

[@sagojez]

Is there a list of what types of variables are monads? List, Futures, Options.. but what else? BTW Great video!!

[@rockthejvm]

Lots of things are monads. Just remember the monad properties. Reader, Writer, Eval, State, IO are other examples of monads.

[@sagojez]

Thank you 😄

[@AntiMyth]

The 127th video on monads that I still don't understand. I've understood every single description and example I've ever watched. Every one of them describes these behaviors and properties. Why though? You need to understand monads because....???

[@ivanvelikanova9950]

This is what I learned about Monads (1) Monad - has a pure constructor, and a flatMap (2) Monad(x).flatMap(f) == f(x) (3) Monad(v).flatMap(x => Monad(x)) == Monad(v) // Useless (4) Monad(v).flatMap(f).flatMap(g) == Monad(v).flatMap(x => f(x).flatMap(g)) I feel so outdated. I seem to have not touch maths for the last 12 years, and nothing other than Java, until a few months ago.

[@oleksii9512]

cool!

[@Orangubara]

After watching this video I feel like Neo disconnected from simulation when he said "I know kung-fu"

[@donwald3436]

Scala users still haven't switched to Kotlin?

[@rockthejvm]

Not until Kotlin has this sort of power

[@francis.joseph]

rocks

[@anzo.p]

genious

[@101graffhead]

>hey bro monads are easy just read an article or two, you will understand them >search monad on youtube >all videos are 30+ minutes h-haha functional programming is cool, oop suck amirite guizzz

[@rockthejvm]

All important questions in life take time to properly sink in.

[@mohamadshaker4236]

The problem with monads is that once you know what is, you lose the ability to explain it

[@ayyubayyyub9415]

The color theme makes it hard and boring to follow, please change the theme to atom one dark theme.

[@luisdominguesforprogramaca3221]

WTF? Is this an explanation for beginners? Of what?

[@rockthejvm]

Still looks like rocket science?

[@apolloartz_5372]

Really helpful video!