I’m reading <https://adventures92.medium.com/kotlin-arrow-kt-eval-monad-a-beginners-guide-bff50e49d0...

# arrow

[Piotr Krzemiński]

I’m reading https://adventures92.medium.com/kotlin-arrow-kt-eval-monad-a-beginners-guide-bff50e49d07c and I’m struggling to understand what’s the point of Eval.
• Eval.now - the author says that “This is the equivalent of just calling a function normally in Kotlin.”
• Eval.later - how is it different from lazy delegated property?
• Eval.always - how is it different from just calling a function each time?
I presume that the examples in the article didn’t fully utilize the power of this monad, like chain it in a creative way. Is it the case? If not, I’d be grateful for any explanation on the above ☝️

[Piotr Krzemiński]

@Anand Verma 🙂 just noticed you’re here on Slack

[simon.vergauwen]

https://github.com/arrow-kt/arrow/pull/2921 😅

[Piotr Krzemiński]

ok, that’s a bit of a bummer from the article’s perspective 😄 could you reveal why you decided to remove them?

[simon.vergauwen]

I’m struggling to understand what’s the point of Eval.

On the JVM we have the issue of stack-safety, and when working over F, or wrappers, you cannot use tailrec. So we there is a need to resort to special tricks to make wrappers stack-safe.

Originally the point of Eval was to create stack-safe implementations of Traverse, but we have since then overcome this need and found simpler solutions.

I.e. we can use tailrec with suspend, and you can use bind with Iterable#map etc. So the need for Eval has kind-of disappeared within the use-case of wrappers.
The Kotlin Std has since then also added DeepRecursiveFunction which when we originally had Eval did not exist.

[Anand Verma]

I guess this article need an update and a bit more explanation.
Thanks you @Piotr Krzemiński for picking it out.

[simon.vergauwen]

@Anand Verma if you want someone to proof read feel free to share it here or in #arrow-contributors ☺️ There is plenty of people happy to help!

[simon.vergauwen]

Same goes for other blogs you plan to write 😉

[Anand Verma]

Thanks @simon.vergauwen thanks a ton for your valuable feedback.