DONT USE THIS - Use JSON Pointer https://github.com/syohex/emacs-json-pointer

get-nested.el

;;; get-nested --- Fetch nodes from nested structures made by json.el
;;; Version: 0.1.0
;;; Author: Jason Milkins jasonm23@gmail.com
;;
;;; Commentary:
;;
;;  The alist/vector payload generated by json.el is very
;;  handy, but Emacs Lisp doesn't (afaik?!) have nice ways to drill
;;  down and cherry pick specific values from the tree.
;;
;;  The examples in json.el don't really dive into this topic very
;;  much, but let's expand on this a little bit.
;;
;;  Using the oxford dictionary REST api as JSON source, let's say we
;;  want to grab the etymology text.
;;
;;  This lives on the following node (JS style)
;;  results[0].lexicalEntries[0].entries[0].etymologies[0]
;;
;;  To fetch from an alist/vector structure we'd need to do:
;;
;;  (elt (cdr (cl-assoc 'etymologies
;;            (elt (cdr (cl-assoc 'entries
;;                      (elt (cdr (cl-assoc 'lexicalEntries
;;                                    (elt (cdr (cl-assoc 'results dictionary-payload))
;;                                         0)))
;;                           0)))
;;             0)))
;;   0)
;;
;;  Even at 2 levels deep this is unpleasant and doing it like this is
;;  quite naive.  We could instead supply a lookup key and extract
;;  the next piece of the structure, by wrapping up the (elt cdr assoc)
;;  part.
;;
;;  We can also wrap the lookup keys into a list and then reduce it
;;  using the structure as the initial-value of the reduce.
;;
;;  Note before we go on, please note this is a very early work in
;;  progress, but it provides the functionality I wanted today.  It
;;  needs work to allow fetching from a specific element index in a
;;  list.
;;
;;  And so some code.
;;
;;; Code:

(eval-when-compile
  (require 'cl))

(defun --get (name structure)
  "Fetch nested vector/alist from json.el by NAME from parent STRUCTURE."
  (elt (cdr (cl-assoc name structure)) 0))

(defun --nested-by (names structure)
  "Fetch nested vector/alist from json.el using a list of NAMES in a STRUCTURE."
  (cl-reduce (lambda (nested-structure name)
               (--get name nested-structure))
             names :initial-value structure))

(provide 'get-nested)

;;; get-nested.el ends here