Dependencies and default implementations about purescript-control HOT 4 CLOSED

Oops, sorry, I meant to undo this change actually. I was intending to copy everything exactly as it is so as not to introduce new problems, and then we could discuss changes like this one.

Feel free to change it back, you should have commit access to all these library repos.

By the sounds of it we should just wait for default implementations before moving zipWithA. I kind of like the idea of having a zipWith in traversable, as then it could take a t a rather than [a]... but Traversable doesn't have a specific order if I remember rightly?

from purescript-control.

It seems like Data.Traversable would be a good place to put zipWithA until we think about implementing defaults, no?

from purescript-control.

Feel free to change it back, you should have commit access to all these library repos.

Nice!

Thinking about it, zipWith is really just a special case of <*> for Array (maybe others?). We should be able to implement an instance for Array that favors zipping, not combinations, so it shouldn't even be needed except to save transforming into and out of the other instance.

newtype ZipArray a = ZipArray [a]

instance Functor ZipArray where
    fmap f (ZipArray xs) = ZipArray (fmap f xs)

instance Applicative ZipArray where
    pure = ZipArray . repeat

    (ZipArray fs) <*> (ZipArray xs) = ZipArray (go fs xs)
        where
        go (g:gs) (y:ys) = g y : go gs ys
        go _      _      = []

Then we could do things like:

(+1) <$> ZipArray [1,2,3]

and we have the same semantics as normal Array

Or use the Applicative to do

(+) <$> ZipArray [1,2,3] <*> pure 1

And have it act like zipWith. Of course this generalizes to arbitrary arity functions like all Applicatives. In other words,

zipWith f xs ys = fromZipArray (f <$> toZipArray xs <*> toZipArray ys)

Or something.

So it should ultimately stay in Control.Applicative or be part of the Data.Array family (which seems more intuitive) once things are all done.

from purescript-control.

Closing this as I guess we must have figured it out at some point in the last year 😉

from purescript-control.