Bring in code from a web essay for parsing data structures
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Howard Abrams
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elisp/query-tree.el
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elisp/query-tree.el
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;;; query-tree.el --- query interface to data structures. -*- lexical-binding: t; -*-
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;;
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;; Copyright © 2023 Howard X. Abrams
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;;
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;; Author: Howard X. Abrams <http://gitlab.com/howardabrams>
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;; Maintainer: Howard X. Abrams <howard.abrams@gmail.com>
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;; Created: April 23, 2023
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;;
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;; This file is not part of GNU Emacs.
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;;
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;;; Commentary:
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;;
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;; A Lisp-focused approach to extracting values from a complex data
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;; structure, similar to how jq works with JSON objects.
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;;
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;; For instance, given a _parsed_ JSON object (a collection of
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;; hash-tables and vectors), like (stored in variable data):
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;;
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;; { "a": 1,
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;; "b": {
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;; "x": 10,
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;; "y": [100, 101, 102, 103],
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;; "z": 30
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;; },
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;; "c": 3
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;; }
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;;
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;; We should be able to call: (query-tree data 'a 'b 2)
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;; Should return 102.
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;;
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;; *NB:* Do not edit this file. Instead, edit the original literate file at:
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;; ~/website/Technical/Emacs/query-data-structures.org
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;; And tangle the file to recreate this one.
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;;
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;;; Code:
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(defun query-tree (data-structure &rest query)
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"Return value from DATA-STRUCTURE based on elements of QUERY."
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(query-tree-parse query data-structure))
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(defun query-tree-parse (query tree)
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"Return value of QUERY from TREE data structure."
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(if (null query)
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tree
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(query-tree-parse (cdr query)
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(query-tree--parse-node (car query) tree))))
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(defun query-tree--parse-node (node tree)
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"Return results of TREE data structure of symbol, NODE.
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If TREE is a hash-table, then NODE would be the key, either a
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string or a symbol. Return value.
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If TREE is a sequence and NODE is number, Return element indexed
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by NODE.
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If TREE is a Property List, return value of NODE as a key. This
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should work with association lists as well."
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(cond
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((null tree) nil)
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((hash-table-p tree) (or (gethash node tree)
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(gethash (symbol-name node) tree)))
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((and (numberp node) (seqp tree)) (seq-elt tree node))
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((and (eq node :first) (seqp tree)) (car node))
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((and (eq node :last) (seqp tree)) (last node))
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((assoc node tree) (alist-get node tree))
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((plistp tree) (plist-get tree node))
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(t (error "query-tree: Looking for '%s' in %s" node tree))))
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(ert-deftest query-tree-walk-tree-test ()
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;; PLIST:
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(let ((data '(:a 1 :b 2 :c 3)))
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(should (eq (query-tree--parse-node :b data) 2)))
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;; ALIST:
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(let ((data '((pine . cones) (oak . acorns) (maple . seeds))))
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(should (eq (query-tree--parse-node 'oak data) 'acorns)))
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;; LIST, aka a sequence
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(let ((data '(a b c d e f)))
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(should (eq (query-tree--parse-node 3 data) 'd)))
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;; VECTOR:
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(let ((data [a b c d e]))
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(should (eq (query-tree--parse-node 2 data) 'c)))
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;; HASH TABLE with strings:
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(let ((h (make-hash-table :test 'equal)))
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(puthash "a" 1 h)
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(puthash "b" 2 h)
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(puthash "c" 3 h)
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(should (eq (query-tree--parse-node "b" h) 2))
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(should (eq (query-tree--parse-node 'b h) 2)))
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;; HASH TABLE with symbols:
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(let ((h (make-hash-table)))
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(puthash 'a 1 h)
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(puthash 'b 2 h)
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(puthash 'c 3 h)
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(should (eq (query-tree--parse-node 'b h) 2))))
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(ert-deftest query-tree-parse-tree-test ()
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(should (null (query-tree-parse nil nil)))
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(let ((data :final))
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(should (eq (query-tree-parse nil data) :final)))
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(let ((data [ a b c d e f ]))
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(should (eq (query-tree-parse '(3) data) 'd)))
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(let ((data (json-parse-string
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"{ \"a\": 1,
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\"b\": {
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\"x\": 10,
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\"y\": [100, 101, 102, 103],
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\"z\": 30
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},
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\"c\": 3
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}")))
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(should (hash-table-p data))
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(should (= (query-tree-parse '("a") data) 1))
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(should (= (query-tree-parse '("b" "x") data) 10))
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(should (= (query-tree-parse '("b" "y" 2) data) 102))
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(should (= (query-tree-parse '(a) data) 1))
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(should (= (query-tree-parse '(b x) data) 10))
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(should (= (query-tree-parse '(b y 2) data) 102))))
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(ert-deftest query-tree-test ()
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(let ((data (json-parse-string
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"{ \"a\": 1,
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\"b\": {
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\"x\": 10,
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\"y\": [100, 101, 102, 103],
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\"z\": 30
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},
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\"c\": 3
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}")))
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(should (= (query-tree data 'b 'y 2) 102))))
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(provide 'query-tree)
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;;; query-tree.el ends here
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