Fanning sums

[treeowl]

I may not understand this properly, but at first glance it seems that fanEither should generalize to something like

fanSum
  :: (GCompare tag, GEnum tag)
  => Event t (DSum tag f) -> DMap tag (Compose (Event t) f)

where GEnum offers a way to enumerate all the tags. (Possible methods: enumTags :: [DSum tag Proxy], enumTagsMap :: DMap tag Proxy).

Simplifying to Identity, that's

fanSumId
  :: (GCompare tag, GEnum tag)
  => Event t (DSum tag Identity) -> DMap tag (Event t)

The idea is that if we have a stream of messages of various types, we should be able to separate it into multiple streams, each of which contains messages of only one type. The big question is whether there's a way to implement this efficiently. I don't have a clue myself.

Note: I've opened an issue for dependent-sum suggesting such a class.

[ryantrinkle]

Have you looked at the `fan` primitive? I think that may do what you're looking for.

…

On Tue, Jun 25, 2019, 15:28 David Feuer ***@***.***> wrote: I may not understand this properly, but at first glance it seems that fanEither should generalize to something like fanSum :: (GCompare tag, GEnum tag) => Event t (DSum tag f) -> DMap tag (Compose (Event t) f) where GEnum offers a way to enumerate all the tags. (Possible methods: enumTags :: [DSum tag Proxy], enumTagsMap :: DMap tag Proxy). Simplifying to Identity, that's fanSumId :: (GCompare tag, GEnum tag) => Event t (DSum tag Identity) -> DMap tag (Event t) The idea is that if we have a stream of messages of various types, we should be able to separate it into multiple streams, each of which contains messages of only one type. The big question is whether there's a way to implement this efficiently. I don't have a clue myself. Note: I've opened an issue <obsidiansystems/dependent-sum#29> for dependent-sum suggesting such a class. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#316?email_source=notifications&email_token=AAI2KYAFSWMMRDM5UDLDJHDP4JWUXA5CNFSM4H3LQB7KYY3PNVWWK3TUL52HS4DFUVEXG43VMWVGG33NNVSW45C7NFSM4G3UGGZA>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAI2KYABJRS735ZQCL2B5MDP4JWUXANCNFSM4H3LQB7A> .

[3noch]

Have you looked at factorEvent?

[treeowl]

@ryantrinkle Ah, I think I see what you mean. Yes, that's probably sufficient, but it seems like overkill. I can turn each DSum into a singleton DMap and use fan with that, but it seems clearer (and at least a bit more efficient) to avoid that.

[treeowl]

@3noch factorEvent doesn't look likely, since it's all about paying attention to when the key changes and I don't care about that.

[ryantrinkle]

Possibly, but the hard work is mostly on the subscriber management side, and it wouldn't be reduced by inputting DSums rather than DMaps. That being said, this all sounds like interesting stuff and I look forward to seeing how it goes!

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On Tue, Jun 25, 2019, 15:41 David Feuer ***@***.***> wrote: @ryantrinkle <https://github.com/ryantrinkle> Ah, I think I see what you mean. Yes, that's probably sufficient, but it seems like overkill. I can turn each DSum into a singleton DMap and use fan with that, but it seems clearer (and at least a bit more efficient) to avoid that. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#316?email_source=notifications&email_token=AAI2KYD37VMKQUGR5WL6633P4JYF7A5CNFSM4H3LQB7KYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGODYRL2XI#issuecomment-505593181>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAI2KYHYOX7DOKBVDD2GKITP4JYF7ANCNFSM4H3LQB7A> .

[treeowl]

If you don't think it matters, then that's fine. It would at least be nice to offer it as a function if not a method, since it takes a bit of mental gymnastics to see that fan does the job.

[treeowl]

Oh, but there is still the matter of type .... Why is fan only for Identity?

[ryantrinkle]

Oh, that could probably be changed. I think it's just a holdover from when DMap was one-argument

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On Tue, Jun 25, 2019, 15:52 David Feuer ***@***.***> wrote: Oh, but there is still the matter of type .... Why is fan only for Identity? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#316?email_source=notifications&email_token=AAI2KYGSZ6PCX3LCPUJPDNDP4JZQXA5CNFSM4H3LQB7KYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGODYRM25A#issuecomment-505597300>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAI2KYEWEE67CMOY3UETWZDP4JZQXANCNFSM4H3LQB7A> .

[oliver-batchelor]

Implemented as PR #318