about summary refs log tree commit diff
path: root/emacs/.emacs.d/wpc/alist.el
blob: 21885b1fc2ee07d0b1a13be07a83741154259d9f (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
;;; alist.el --- Interface for working with associative lists -*- lexical-binding: t -*-
;; Author: William Carroll <wpcarro@gmail.com>

;;; Commentary:
;; Firstly, a rant:
;; In most cases, I find Elisp's APIs to be confusing.  There's a mixture of
;; overloaded functions that leak the implementation details (TODO: provide an
;; example of this.) of the abstract data type, which I find privileges those
;; "insiders" who spend disproportionately large amounts of time in Elisp land,
;; and other functions with little-to-no pattern about the order in which
;; arguments should be applied.  In theory, however, most of these APIs could
;; and should be much simpler.  This module represents a step in that direction.
;;
;; I'm modelling these APIs after Elixir's APIs.
;;
;; On my wishlist is to create protocols that will allow generic interfaces like
;; Enum protocols, etc.  Would be nice to abstract over...
;; - associative lists (i.e. alists)
;; - property lists (i.e. plists)
;; - hash tables
;; ...with some dictionary or map-like interface.  This will probably end up
;; being quite similar to the kv.el project but with differences at the API
;; layer.
;;
;; Similar libraries:
;; - map.el: Comes bundled with recent versions of Emacs.
;; - asoc.el: Helpers for working with alists.  asoc.el is similar to alist.el
;;   because it uses the "!" convention for signalling that a function mutates
;;   the underlying data structure.
;; - ht.el: Hash table library.
;; - kv.el: Library for dealing with key-value collections.  Note that map.el
;;   has a similar typeclass because it works with lists, hash-tables, or
;;   arrays.
;; - a.el: Clojure-inspired way of working with key-value data structures in
;; Elisp.  Works with alists, hash-tables, and sometimes vectors.
;;
;; Some API design principles:
;; - The "noun" (i.e. alist) of the "verb" (i.e. function) comes last to improve
;; composability with the threading macro (i.e. `->>') and to improve consumers'
;; intuition with the APIs.  Learn this once, know it always.
;;
;; - Every function avoids mutating the alist unless it ends with !.
;;
;; - CRUD operations will be named according to the following table:
;;   - "create" *and* "set"
;;   - "read"   *and* "get"
;;   - "update"
;;   - "delete" *and* "remove"
;;
;; For better or worse, all of this code expects alists in the form of:
;; ((first-name . "William") (last-name . "Carroll"))
;;
;; Special thanks to github.com/alphapapa/emacs-package-dev-handbook for some of
;; the idiomatic ways to update alists.
;;
;; TODO: Include a section that compares alist.el to a.el from
;; github.com/plexus/a.el.

;; Dependencies:

;; TODO: Consider dropping explicit dependency white-listing since all of these
;; should be available in my Emacs.  The problem arises when this library needs
;; to be published, in which case, something like Nix and a build process could
;; possible insert the necessary require statements herein.  Not sure how I feel
;; about this though.
(require 'maybe)
(require 'macros)
(require 'dash)
(require 'tuple)
(require 'maybe)

;;; Code:

;; TODO: Support function aliases for:
;; - create/set
;; - read/get
;; - update
;; - delete/remove

;; Support mutative variants of functions with an ! appendage to their name.

;; Ensure that the same message about only updating the first occurrence of a
;; key is consistent throughout documentation using string interpolation or some
;; other mechanism.

;; TODO: Consider wrapping all of this with `(cl-defstruct alist xs)'.

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Constants
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(defconst alist/enable-tests? t
  "When t, run the test suite.")

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Library
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;; TODO: Support a variadic version of this to easily construct alists.
(defun alist/new ()
  "Return a new, empty alist."
  '())

;; Create
;; TODO: See if this mutates.
(defun alist/set (k v xs)
  "Set K to V in XS."
  (if (alist/has-key? k xs)
      (progn
        (setf (alist-get k xs) v)
        xs)
    (list/cons `(,k . ,v) xs)))

(defun alist/set! (k v xs)
  "Set K to V in XS mutatively.
Note that this doesn't append to the alist in the way that most alists handle
  writing.  If the k already exists in XS, it is overwritten."
  (map-delete xs k)
  (map-put xs k v))

;; Read
(defun alist/get (k xs)
  "Return the value at K in XS; otherwise, return nil.
Returns the first occurrence of K in XS since alists support multiple entries."
  (cdr (assoc k xs)))

(defun alist/get-entry (k xs)
  "Return the first key-value pair at K in XS."
  (assoc k xs))

;; Update
;; TODO: Add warning about only the first occurrence being updated in the
;; documentation.
(defun alist/update (k f xs)
  "Apply F to the value stored at K in XS.
If `K' is not in `XS', this function errors.  Use `alist/upsert' if you're
interested in inserting a value when a key doesn't already exist."
  (if (maybe-nil? (alist/get k xs))
      (error "Refusing to update: key does not exist in alist")
    (alist/set k (funcall f (alist/get k xs)) xs)))

(defun alist/update! (k f xs)
  "Call F on the entry at K in XS.
Mutative variant of `alist/update'."
  (alist/set! k (funcall f (alist/get k xs))xs))

;; TODO: Support this.
(defun alist/upsert (k v f xs)
  "If K exists in `XS' call `F' on the value otherwise insert `V'."
  (if (alist/get k xs)
      (alist/update k f xs)
    (alist/set k v xs)))

;; Delete
;; TODO: Make sure `delete' and `remove' behave as advertised in the Elisp docs.
(defun alist/delete (k xs)
  "Deletes the entry of K from XS.
This only removes the first occurrence of K, since alists support multiple
  key-value entries.  See `alist/delete-all' and `alist/dedupe'."
  (remove (assoc k xs) xs))

(defun alist/delete! (k xs)
  "Delete the entry of K from XS.
Mutative variant of `alist/delete'."
  (delete (assoc k xs) xs))

;; Additions to the CRUD API
;; TODO: Implement this function.
(defun alist/dedupe-keys (xs)
  "Remove the entries in XS where the keys are `equal'.")

(defun alist/dedupe-entries (xs)
  "Remove the entries in XS where the key-value pair are `equal'."
  (delete-dups xs))

(defun alist/keys (xs)
  "Return a list of the keys in XS."
  (mapcar 'car xs))

(defun alist/values (xs)
  "Return a list of the values in XS."
  (mapcar 'cdr xs))

(defun alist/has-key? (k xs)
  "Return t if XS has a key `equal' to K."
  (maybe-some? (assoc k xs)))

(defun alist/has-value? (v xs)
  "Return t if XS has a value of V."
  (maybe-some? (rassoc v xs)))

(defun alist/count (xs)
  "Return the number of entries in XS."
  (length xs))

;; TODO: Should I support `alist/find-key' and `alist/find-value' variants?
(defun alist/find (p xs)
  "Apply a predicate fn, P, to each key and value in XS and return the key of
  the first element that returns t."
  (let ((result (list/find (lambda (x) (funcall p (car x) (cdr x))) xs)))
    (if result
        (car result)
      nil)))

(defun alist/map-keys (f xs)
  "Call F on the values in XS, returning a new alist."
  (list/map (lambda (x)
              `(,(funcall f (car x)) . ,(cdr x)))
            xs))

(defun alist/map-values (f xs)
  "Call F on the values in XS, returning a new alist."
  (list/map (lambda (x)
              `(,(car x) . ,(funcall f (cdr x))))
            xs))

(defun alist/reduce (acc f xs)
  "Return a new alist by calling F on k v and ACC from XS.
F should return a tuple.  See tuple.el for more information."
  (->> (alist/keys xs)
       (list/reduce acc
                    (lambda (k acc)
                      (funcall f k (alist/get k xs) acc)))))

(defun alist/merge (a b)
  "Return a new alist with a merge of alists, A and B.
In this case, the last writer wins, which is B."
  (alist/reduce a #'alist/set b))

;; TODO: Support `-all' variants like:
;; - get-all
;; - delete-all
;; - update-all

;; Scratch-pad
(macros/comment
 (progn
   (setq person '((first-name . "William")
                  (first-name . "William")
                  (last-name  . "Carroll")
                  (last-name  . "Another")))
   (alist/set 'last-name "Van Gogh" person)
   (alist/get 'last-name person)
   (alist/update 'last-name (lambda (x) "whoops") person)
   (alist/delete 'first-name person)
   (alist/keys person)
   (alist/values person)
   (alist/count person)
   (alist/has-key? 'first-name person)
   (alist/has-value? "William" person)
   ;; (alist/dedupe-keys person)
   (alist/dedupe-entries person)
   (alist/count person)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Tests
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(when alist/enable-tests?
  (prelude-assert
   (equal '((2 . one)
            (3 . two))
          (alist/map-keys #'1+
                          '((1 . one)
                            (2 . two)))))
  (prelude-assert
   (equal '((one . 2)
            (two . 3))
          (alist/map-values #'1+
                            '((one . 1)
                              (two . 2))))))


;; TODO: Support test cases for the entire API.

(provide 'alist)
;;; alist.el ends here