# Is the Maybe Monad Instance ever good?

**URL:** <https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133>\
**Category:** Learn\
**Created:** [October 18, 2025, 4:59pm UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133 "2025-10-18T16:59:10Z")\
**Posts on this page:** 20\
**Page:** 1

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**Author:** ![eldritch-cookie](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/eldritch-cookie/32/4130_2.png) [@eldritch-cookie](https://discourse.haskell.org/u/eldritch-cookie)\
**Post date:** [October 18, 2025, 4:59pm UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/1 "2025-10-18T16:59:10Z")

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The one principle i know about the Maybe type is that we shouldn’t use it when there is more than one failure reason, however if i use monadic functions in the construction of my Maybe value there are exactly 0 generic ways to decipher why i have a Nothing value in the case i do.

Also it isn’t like there are no alternatives assuming you can’t add non boot dependencies you can easily use the (Either SomeException) monad and this also allows you to use all the exception stuff in Control.Monad.Catch.  
If you can add a dependency in a library with polymorphic variants you can have even more correctness, eliminating errors partially instead of being forced to handle all possible Exceptions to eliminate

given these facts is there a situation where the Maybe Monad Instance is the best option?

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**Author:** ![treblacy](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/treblacy/32/1782_2.png) [@treblacy](https://discourse.haskell.org/u/treblacy)\
**Post date:** [October 18, 2025, 7:40pm UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/2 "2025-10-18T19:40:30Z")

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I have had many occassions when there is only failure reason or the reason is irrelevant to my plan B. The most boring example is `Data.Map[.Strict].lookup`; slightly less boring example is when I’m going for `catMaybes . map (lookup foo)`.

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**Author:** ![eldritch-cookie](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/eldritch-cookie/32/4130_2.png) [@eldritch-cookie](https://discourse.haskell.org/u/eldritch-cookie)\
**Post date:** [October 18, 2025, 7:50pm UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/3 "2025-10-18T19:50:45Z")

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Did it never occur to you a situation that you get a Nothing in a function which uses the Maybe Monad Instance(probably do syntax) to produce the final value and then you waste a ton of time looking into which of the monadic function calls generates the failure?  
How do you reliably prevent this situation? i am not against Maybe only all uses of (\>\>=) instantiated on this type.

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**Author:** ![rhendric](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/rhendric/32/2689_2.png) [@rhendric](https://discourse.haskell.org/u/rhendric)\
**Post date:** [October 18, 2025, 8:06pm UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/4 "2025-10-18T20:06:50Z")

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Seems like this is an argument against using `Nothing` to represent errors you may want to diagnose, not an argument against using `Monad Maybe` ever.

If `Nothing` means ‘unnecessary’, for example, then it’s perfectly reasonable to use it monadically; you’re expressing that you don’t care why you don’t need a thing. If you do care why, you have the wrong type.

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**Author:** ![darkxero](https://avatars.discourse-cdn.com/v4/letter/d/f07891/32.png) [@darkxero](https://discourse.haskell.org/u/darkxero)\
**Post date:** [October 19, 2025, 5:37am UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/5 "2025-10-19T05:37:43Z")

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When you do a database query with left joins and you retrieve 10 fields per row which might be null and you want to do something with them (it’s not an error and you don’t want to log the nulls).

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**Author:** ![enobayram](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/enobayram/32/1815_2.png) [@enobayram](https://discourse.haskell.org/u/enobayram)\
**Post date:** [October 20, 2025, 1:51am UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/6 "2025-10-20T01:51:58Z")

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Programming is the art of controlled forgetfulness. After all pure logic can only forget information, it can never create new information. You use the Maybe monad whenever it provides precisely the right kind of forgetting you need.

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**Author:** ![iteratee](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/iteratee/32/4332_2.png) [@iteratee](https://discourse.haskell.org/u/iteratee)\
**Post date:** [October 20, 2025, 3:26am UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/7 "2025-10-20T03:26:43Z")

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A lot of the container code returns `Nothing` for a nonexistent value. So if you ever need to chain lookups (lookup in map A, then if it exists lookup in map B) the maybe Monad is perfect for this.

I used it (as a transformer) recently [when two things could be not-present](https://github.com/iteratee/cql-io/blob/master/src/lib/Database/CQL/IO/Client.hs#L1640C1-L1647C47).

Yes, it’s often useful to know the failure reason, but sometimes there is exactly one failure reason.

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**Author:** ![eldritch-cookie](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/eldritch-cookie/32/4130_2.png) [@eldritch-cookie](https://discourse.haskell.org/u/eldritch-cookie)\
**Post date:** [October 21, 2025, 5:01pm UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/8 "2025-10-21T17:01:04Z")

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how exactly does this use case, use the Maybe.(\>\>=) method? this is using Maybe as a ADT which is always fine unless you shouldn’t use Maybe at all.

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**Author:** ![eldritch-cookie](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/eldritch-cookie/32/4130_2.png) [@eldritch-cookie](https://discourse.haskell.org/u/eldritch-cookie)\
**Post date:** [October 21, 2025, 5:07pm UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/9 "2025-10-21T17:07:05Z")

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yes and once again the problem is that when you will eventually get a Nothing you won’t know which of the Maybes failed. Once again although for each individual function a Maybe may make sense a Maybe produced monadically is always bad as it has at least 2 possible different failure reasons

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**Author:** ![iteratee](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/iteratee/32/4332_2.png) [@iteratee](https://discourse.haskell.org/u/iteratee)\
**Post date:** [October 21, 2025, 5:45pm UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/10 "2025-10-21T17:45:22Z")

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It only matters which one failed if you care which one failed. You’re welcome to not like it and not use it in your code. Asserting that it is always bad is a bit dictatorial for the rest of us.

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**Author:** ![eldritch-cookie](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/eldritch-cookie/32/4130_2.png) [@eldritch-cookie](https://discourse.haskell.org/u/eldritch-cookie)\
**Post date:** [October 21, 2025, 7:55pm UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/11 "2025-10-21T19:55:12Z")

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??? having the opinion that something is bad and discussing it. Is inherently dictatorial ??? “using unsafePeformIO is bad long term. Don’t use it” that is dictatorial??

If not please enlighten me on what is the dictatorial difference between this and “using the Maybe Monad Instance(\>\>=) is bad. Don’t use it”? also the worst wrong answer is “the second is dictatorial because i disagree with it”.

How could anything discussed on this Forum be dictatorial without being about moderation? also even assuming definition 2 of [merriam webster](https://www.merriam-webster.com/dictionary/dictatorial).

i don’t think i have been Oppressive, Arrogant or Overbearing? if i have been unintentionally could you point exactly how so that i can learn for next time?

anyways code changes. How do you know when to convert your own code from Maybe to some other error handling monad like (Either SomeException) ?

I really don’t know how to do this consistently and frequently mistakenly under consider the consequences of a consumer of my code needing to know about which monadic values are Nothing.

I have many considerations like this but talking about all of them simultaneously would distract from those a consider most important, thanks for the understanding.

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**Author:** ![iteratee](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/iteratee/32/4332_2.png) [@iteratee](https://discourse.haskell.org/u/iteratee)\
**Post date:** [October 21, 2025, 8:16pm UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/12 "2025-10-21T20:16:41Z")

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I was responding to

> is always bad

Specifically. That kind of categorical dismissal is unhelpful. So is a wall of text in response to word choice.

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**Author:** ![augustss](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/augustss/32/887_2.png) [@augustss](https://discourse.haskell.org/u/augustss)\
**Post date:** [October 21, 2025, 10:02pm UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/13 "2025-10-21T22:02:11Z")

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I frequently use the Maybe monad and it works perfectly well. Of course, if I do need to know exactly what “failed", I use something else.

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**Author:** ![darkxero](https://avatars.discourse-cdn.com/v4/letter/d/f07891/32.png) [@darkxero](https://discourse.haskell.org/u/darkxero)\
**Post date:** [October 22, 2025, 3:24am UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/14 "2025-10-22T03:24:58Z")

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I was thinking that rather than making a big left to right case pattern matching (or nesting cases if some items must be combined with others) over 10 values you can use do notation (thus, \>\>=) and it’s easier to structure, top to bottom, no extra indentation. Easier to look at when you start progressing through the items.

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**Author:** ![tobz619](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/tobz619/32/3125_2.png) [@tobz619](https://discourse.haskell.org/u/tobz619)\
**Post date:** [October 22, 2025, 6:58am UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/15 "2025-10-22T06:58:30Z")

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I can kind of see where you’re coming from. The only time I find it super necessary are when:

1. Working with nested lookups

2. Sequencing functions that can fail –\> but even here I find `Applicative Maybe` more useful.

I think it’s fine whenever `Nothing` is representing “there is nothing useful I can do with the result of this computation” and if a sequence of monadic `Maybe` actions can be sequenced to represent one big idea (i.e, all of these procedures in this specific sequence must pass, otherwise, any single failure in here will be handled equally).

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**Author:** ![effectfully](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/effectfully/32/3266_2.png) [@effectfully](https://discourse.haskell.org/u/effectfully)\
**Post date:** [October 22, 2025, 8:32am UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/16 "2025-10-22T08:32:28Z")

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`Maybe` is definitely overused and I’ve committed sins of this sort myself, which I’ve lived to regret.

That said, not all `Nothing`s get reported. One good example is transforming an AST by spotting certain patterns in it. You define things like `viewLambdaApplication :: Term -> Maybe Term`, `viewConstant :: Term -> Maybe Constant` etc, chain them together and if you get a `Nothing`, it’s fine, you move on to trying the same thing with a subtree or just give up.

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**Author:** ![eldritch-cookie](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/eldritch-cookie/32/4130_2.png) [@eldritch-cookie](https://discourse.haskell.org/u/eldritch-cookie)\
**Post date:** [October 22, 2025, 2:58pm UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/17 "2025-10-22T14:58:51Z")

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i am not saying to not use do notation, i am fully in favor of using do notation with a better error-monad like (Either SomeException) or anything equivalent to VEither from vary, just don’t do so when your type is maybe.

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**Author:** ![jackdk](https://avatars.discourse-cdn.com/v4/letter/j/9f8e36/32.png) [@jackdk](https://discourse.haskell.org/u/jackdk)\
**Post date:** [October 22, 2025, 9:02pm UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/18 "2025-10-22T21:02:57Z")

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I find the `Monad` instances for `Maybe` and `Either e` useful, but unlike monads that are used to organise side-effects, there’s usually less complicated control flow and less reason to use large `do`-blocks. So when I choose to use a `do`-block with them, I’ll often write `Just` or `Right` instead of `pure` because they’re relatively uncommon.

EDIT: I also do this with the list monad, writing `[foo]` at the end of a block of code to make things clearer.

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**Author:** ![olf](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/olf/32/3813_2.png) [@olf](https://discourse.haskell.org/u/olf)\
**Post date:** [October 23, 2025, 1:47pm UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/19 "2025-10-23T13:47:19Z")

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The core misunderstanding here is that `Nothing` is always to be interpreted as some kind of failure. But `Maybe x` is simply the monad of sub-sets of `x` with cardinality at most one. In that role, `Maybe` is perfectly fine as it is, as other have pointed out.

Of course you are right that conflating meaningfully different kinds of failure is bad programming style.

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**Author:** ![Swordlash](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/swordlash/32/5817_2.png) [@Swordlash](https://discourse.haskell.org/u/Swordlash)\
**Post date:** [October 25, 2025, 1:23pm UTC](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133/20 "2025-10-25T13:23:02Z")

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One of my favourite uses of Maybe monad is abusing its MonadFail instance. So I can pattern match on stuff and fail fast if something does not match.

[Next page](https://discourse.haskell.org/t/is-the-maybe-monad-instance-ever-good/13133.md?page=2)