Conversions between nested pairs and HLists

[mgzuber]

No description provided.

[codecov-io]

Codecov Report

Merging #701 into master will increase coverage by 0.07%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #701      +/-   ##
==========================================
+ Coverage   87.99%   88.07%   +0.07%     
==========================================
  Files          64       64              
  Lines        1499     1509      +10     
  Branches        7        7              
==========================================
+ Hits         1319     1329      +10     
  Misses        180      180

Impacted Files	Coverage Δ
...e/src/main/scala/shapeless/syntax/std/tuples.scala	83.72% <100%> (+0.19%)	⬆️
core/src/main/scala/shapeless/syntax/hlists.scala	90.07% <100%> (+0.07%)	⬆️
core/src/main/scala/shapeless/ops/hlists.scala	93.44% <100%> (+0.12%)	⬆️

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[mgzuber]

@milessabin Any comments either way?

[milessabin]

Yes, this looks useful. The corresponding definitions for nested Either to `Coproducts would also be useful. I think there are a couple of issue which need to be resolved though.

First you've reused a lot of existing names (eg. ToHList) and added names which are very close to existing names (eg. toTuple vs. tupled). Can you come up with something which distinguishes your additions from what's already there and more clearly illustrates the different semantics?

Second, I'm not completely convinced at the way the nested pairs are terminated ... why not have () as the rightmost element, analogous to HNil?

[milessabin]

I'll consider merging this if you rebase and address the issues raised in my previous comment.

[mgzuber]

My apologies on having been MIA.

To address your above comments.

• The definitions for nested Either to Coproduct was already merged in Conversions between Coproducts and Eithers #699.
• I couldn't find a similar name to toHList in the tuple syntax. I'm of the opinion that this is a reasonable name, but am more than happy to change it if you still disagree
• I changed toTuple to nestedProduct
• Your second point is one of preference I think. I thought it convenient to be able to convert a 2-tuple directly to a HList and a length 2 HList directly to a 2-tuple. However, I don't have a strong opinion on this, so I've changed the behaviour to be as you described.

Let me know if you'd like more changes, I will get to them quickly!