Make Zipper opaque. Add fromCons and from constructors

[AdrianoFerrari]

Basic attempt to make Zipper private (#10). Added two new constructors as well, since it would probably be useful to have these.

[AdrianoFerrari]

Looking forward to discussion, @wernerdegroot . I think making Zipper private is an important API change. What would be the next steps to get this (or something similar) merged? Thoughts?

[wernerdegroot]

Hi @AdrianoFerrari , thanks for contributing. Although I haven't responded really quickly, I really appreciate you taking the time 👍

I would like to propose to add a few unit tests for the new functions.

Also, the fact that the Zipper constructors are now private is breaking the currently existing tests. Could you take a look at that too? Maybe it's a good idea to add a function to construct it from a beforeReversed, current and after so people can migrate easily? That could be useful for fixing the tests too!

[AdrianoFerrari]

Thanks for the feedback!
I'll try to bring the tests in line, and see about that "beforeReversedetc." constructor.

[AdrianoFerrari]

Fixed the existing tests, still need to add unit tests for new functions.

I'm worried about introducing the fromBeforeReversed constructor (or whatever we'd call it), because it's bringing back the confusion that opaque zippers were meant to fix.

Anyone that was using the Zipper constructor directly would have been adding a List.reverse to the before term. Migration will be as easy as removing that reversal. I'd say that clarifying the docs for the from constructor would be enough to ensure smooth migration.

Thoughts?

[AdrianoFerrari]

Added new unit tests, and doc clarification for from constructor.

[wernerdegroot]

Nice! The comment should help a lot!

[wernerdegroot]

Thanks for your contribution. I'll release this directly!

[wernerdegroot]

Published as 4.0.0! Well done!

[AdrianoFerrari]

Yay 🎉!
Thanks for the guidance and feedback.