Make Cmd a Monoid and/or Applicative/Monad about purescript-bonsai HOT 7 CLOSED

Implementing the Applicative instance has the same problem the monad has: it would be necessary to collect all the results before combining. This would completely change the semantics .. e.g for an animation it would loose all the delays (and thus, all intermediate steps).

Monoid should be possible though

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Not enough bang for the buck, will not be implemented

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Things change, the bang/buck ratio just increased.

The update function returns a (Tuple (Cmd eff msg) model) now - if Cmd was a monoid, the result tuples would be Applicatives.

Only problem: circular dependencies - to define the monoid instance, you need Cmd and emitMessage in one place. A lot of stuff would have to move to VirtualDom.purs

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Still won't implement the Monad/Applicative instances though.

An emittingTask can call it's emitter multiple times. It would be possible to wait for the values with an AVar, and somehow signal the end when the emittingTask ends, but why? Pure commands are an array, just compose that. And the task commands are Aff actions - they are fully composable as well.

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Oops, I made a monad instance. This lets us define empty and pure ... kill emptyCommand and pureCommand?

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Having worked with the new combinators: this is awesome.

I want a parallel apply, and alt should choose the first message that arrives on either stream of messages.

Not sure yet whether bind and apply should permute or zip. I suspect zipping would be more useful, but I'll have to think about it some more.

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This is in https://github.com/grmble/purescript-bonsai-types now.

bind/apply have permute semantics, like array and other collections. append has string ordering, alt forwards any message that comes in.

Still missing: parallel apply, racing operator. Worth the effort? Dunno.

grmble/purescript-bonsai-types#1

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