feat: add Uniplate::holes and Uniplate::contexts

[niklasdewally]

Port holes and context functions from the original Haskell library.

[niklasdewally]

@ozgurakgun would appreciate a sanity check for this.

[ozgurakgun]

Looks good! What's left before we have full zippers then? Now that we have holes and contexts, I think it's just the traversal functions, isn't it?

[niklasdewally]

Looks good! What's left before we have full zippers then? Now that we have holes and contexts, I think it's just the traversal functions, isn't it?

Yep!

[ozgurakgun]

I only checked in my phone without running anything btw. One thing this made me think is whether we want iterators instead of vectors for some of the other functions too.

We never did performance profiling so hard to know.

[niklasdewally]

I only checked in my phone without running anything btw. One thing this made me think is whether we want iterators instead of vectors for some of the other functions too.

Thats the long-term goal. Still not sure whether to make the default operations return an iterator, or have a seperate iterator API though!

Also, the internal tree datastructure is not lazy yet...