This is immediately solved by Lenses

    _Object . key "them" . key "public_keys" . key "primary" . key "bundle"

which you might complain saying that this is yet another idiosyncratic method of traversing data types. In fact this whole thread is full of examples of other idiosyncratic methods of traversing (JSON only) data types.

Except lenses aren't. Lenses are highly principled and compose and combine in ridiculous ways while maintaining their exact behavior. Half the features proposed in this thread exist naturally and "emergently" by the nature of lenses. Finally, they follow mathematical laws describing how everything should work together all to the T.

At the highest level a Lens is a getter plus a setter bound together. You can extract either component to get or set a subpart of a value.

At the next level, you can take note that lenses "compose" (as a category) by letting you reach deeper and deeper into a structure. This is what I took advantage of with the JSON example above: composing them with `(.)`.

At the next level, lenses generalize naturally to "traversals" which target multiple subparts all at once and "folds" which build exotic "getters" over multiple targeted subparts.

At the next level, lenses "dualize" to prisms which deal with branching types. This is hard to explain if you haven't used a language with a true sum type (Scala, Haskell, ML, and lets not get into lazy/strict sums) but I used one above to traverse into the "Object" indicating failure if my assumption of the structure of the JSON blob were wrong.

At the next level you generalize these into isomorphisms which have nice mathematical properties determining when two types are identical by giving you invertible mappings between the two. This is like a lens which focuses on the entire type as its "subpart".

(http://hackage.haskell.org/package/lens)

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At the end of the day there are even more steps in that hierarchy. It sounds ridiculously complex, and it is a little bit to learn. The advantage is, however, that the intuition of "focusing on a subpart" applies over any data type and with pretty near any weird combination of "lens-like" operators you can dream up.

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Usually when someone first hears about lenses they say "Oh, getters and setters. I have those already, no big deal". That's really far from the case, however... Lenses end up being the XPath of everything.