Merge Prism and Optional about elm-monocle

[andys8]

Interesting. I didn't know it doesn't exist in Haskell. It does in Scala and TypeScript.

For me, not coming from Haskell, it looks like they serve a different purpose and have different type signatures. Prism converts structures, Optional sets nested values.

https://mobile.twitter.com/puffnfresh/status/654862731548446720

https://stackoverflow.com/questions/33725534/are-monocles-optionals-the-same-as-partial-lenses

I'm not arguing for one or the other. Instead I'm curious how it's done in Haskell and what the advantages of removing Optional are and how its usages will be replaced.

[arturopala]

I'm happy and welcome to accept PRs but would like to keep things backward compatible when reasonable, i.e. not forced by the ELM changes. czw., 25 lip 2019, 01:17 użytkownik Andy <[email protected]> napisał:

…

Interesting. I didn't know it doesn't exist in Haskell. It does in Scala <https://julien-truffaut.github.io/Monocle/optics/optional.html>. For me, not coming from Haskell, it looks like they serve a different purpose and have different type signatures. Prism converts structures, Optional sets nested values. https://mobile.twitter.com/puffnfresh/status/654862731548446720 https://stackoverflow.com/questions/33725534/are-monocles-optionals-the-same-as-partial-lenses I'm not arguing for one or the other. Instead I'm curious how it's done in Haskell and what the advantages of removing Optional are. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#26?email_source=notifications&email_token=AAB5IL2ZMOSFBC4WCNMDVO3QBDPJFA5CNFSM4H7GEC52YY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOD2X32VY#issuecomment-514833751>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAB5ILY5RPB2OYM2ULZBFKDQBDPJFANCNFSM4H7GEC5Q> .

[nikita-volkov]

For me, not coming from Haskell, it looks like they serve a different purpose and have different type signatures. Prism converts structures, Optional sets nested values.

Actually, I've screwed up and you've helped me realise it. Thanks!

Prism does the same thing in Haskell as both in this library and Scala. Haskell does in fact lack Optional: see the abstractions hierarchy (from the "lens" library). It however does have a thing that achieves the same purpose as Optional, only in a more general way: it's Traversal and the difference is that it lets you point at multiple locations.

This made me google for traversals in Scala's Monocle, and I've discovered that the library has both Traversal and Optional: https://julien-truffaut.github.io/Monocle/optics/traversal.html. So while I still am not sold on the usefulness of Optional, since we don't have Traversal here yet, it's better that we have that at least. I'll close the issue.

[andys8]

Thanks @nikita-volkov, I learned something.

I am wondering how traversals (#24) should be implemented and if they're useful for something else than List. They could work for Array, Maybe and other container's though. I would like to play around with them. The API will probably look like those in other languages without type classes.