Add zipLeft, zipRight methods (as addition to zip method) to ZStream and equivalent operators

[nicolasdasriaux]

On ZStream:

• Add crossWith(f: (A, B) => C), equivalent to ls.flatMap(l => rs.map(f)
• Add cross / <*>, equivalent to crossWith((_, _))
• Add <*, equivalent to (l <*> r).map(_._1)
• Add *>, equivalent to (l <*> r).map(_._2)
• Add <&>, an alias for zip
• Add zipLeft and <&, equivalent to (l <&> r).map(_._1)
• Add zipRight and &>, equivalent to (l <&> r).map(_._2)

[iravid]

For consistency, the <*> variants should be based on flatMap, while the <&> should be based on zipWith.

If we were ultra-consistent, zipWith itself would have another name. But that's already been decided by other streaming libraries.

Also, I don't think we neeed &&&.

I'll update the description.

[jdegoes]

@iravid Don't we need zipWith and zipWithPar, and their variants (left/right)?

[nicolasdasriaux]

So would that imply something like that ?

Renaming

• Rename current zipWith to zipParWith
• Rename current zip to zipPar

zipParWith family

• Add <&>, an alias for zipPar
• Add zipParLeft and <&, equivalent to (l <&> r).map(_._1)
• Add zipParRight and &>, equivalent to (l <&> r).map(_._2)

zipWith familly

• Add zipWith
• Add zip and <*> , equivalent to ls.flatMap(l => rs.map((l, _)))
• Add zipLeft and <*, equivalent to (l <*> r).map(_._1)
• Add zipRight and *>, equivalent to (l <*> r).map(_._2)

[iravid]

@jdegoes

We have ZStream#zipWith currently, which runs two streams in parallel. We don't have a named operator for ls.flatMap(l => rs.map(r => (l, r))).

@jdegoes @nicolasdasriaux

As I mentioned above, renaming the current zipWith to zipWithPar would be the most consistent. But keep in mind that this is inconsistent with the Scala collections library. Beyond that, most people I've worked with automatically reach for zipWith as the operator with the current semantics, and not zipParWith.

[jdegoes]

@iravid OK, it bothers me a bit but in cases where we only have one variant, we do omit the Par prefix. Of course we could flip it in this case, zipWithSeq for the other one, although crossWith would be better.

[iravid]

cross is a great idea. I will update the description.

[ghostdogpr]

Closed by #1510