add more examples to foldable.md

[stew]

No description provided.

[codecov-io]

Current coverage is 89.30%

Merging #824 into master will increase coverage by +0.18% as of 8cf484d

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  Files          168    168       
  Stmts         2309   2319    +10
  Branches        75     75       
  Methods          0      0       
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+ Hit           2058   2071    +13
  Partial          0      0       
+ Missed         251    248     -3

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[adelbertc]

👍

[ceedubs]

I think that (a,b) => Eval.now(a && b.value) would need to be something like (a,b) => if (a) b else Eval.now(false) in order to be stack safe if there were say 10k true values prepending the continually false values. So it might be a good idea to avoid calling .value until the very end, since that's what you usually want to do with Eval to achieve stack safety.

Having said that, I just gave it a try and it looks like the Cats foldRight implementation for Stream isn't actually stack safe. I'll create a separate issue for that.

[stew]

I really mean this as a toy example to demonstrate the laziness. I think that it is clearer to read as is. but if you say please I'll change it :)

[ceedubs]

Hmm yeah, I see your point. It just seems bad to me to write an implementation that isn't stack-safe when a few lines above calls out that the std lib foldRight would hit a stack overflow. And if this is where people come to learn about foldRight, I'd want them to see examples of how to do it "right". I don't want to be a stick in the mud here though, so maybe I should just let it go :)

[ceedubs]

I guess I should have just said "please" :)

Thanks, @stew! Good stuff.