emacs/lisp/emacs-lisp/map.el

;;; map.el --- Map manipulation functions  -*- lexical-binding: t; -*-

;; Copyright (C) 2015 Free Software Foundation, Inc.

;; Author: Nicolas Petton <nicolas@petton.fr>
;; Keywords: convenience, map, hash-table, alist, array
;; Version: 1.0
;; Package: map

;; Maintainer: emacs-devel@gnu.org

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with this program.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; map.el provides map-manipulation functions that work on alists,
;; hash-table and arrays.  All functions are prefixed with "map-".
;;
;; Functions taking a predicate or iterating over a map using a
;; function take the function as their first argument.  All other
;; functions take the map as their first argument.

;; TODO:
;; - Add support for char-tables
;; - Maybe add support for gv?
;; - See if we can integrate text-properties
;; - A macro similar to let-alist but working on any type of map could
;;   be really useful

;;; Code:

(require 'seq)

(defun map-elt (map key &optional default)
  "Perform a lookup in MAP of KEY and return its associated value.
If KEY is not found, return DEFAULT which defaults to nil.

If MAP is a list, `equal' is used to lookup KEY."
  (map--dispatch map
    :list (or (cdr (assoc key map)) default)
    :hash-table (gethash key map default)
    :array (map--elt-array map key default)))

(defmacro map-put (map key value)
  "In MAP, associate KEY with VALUE and return MAP.
If KEY is already present in MAP, replace the associated value
with VALUE."
  (declare (debug t))
  `(progn
     (map--dispatch (m ,map m)
       :list (setq ,map (cons (cons ,key ,value) m))
       :hash-table (puthash ,key ,value m)
       :array (aset m ,key ,value))))

(defmacro map-delete (map key)
  "In MAP, delete the key KEY if present and return MAP.
If MAP is an array, store nil at the index KEY."
  (declare (debug t))
  `(progn
     (map--dispatch (m ,map m)
       :list (setq ,map (map--delete-alist m ,key))
       :hash-table (remhash ,key m)
       :array (map--delete-array m ,key))))

(defun map-nested-elt (map keys &optional default)
  "Travserse MAP using KEYS and return the looked up value or DEFAULT if nil.
Map can be a nested map composed of alists, hash-tables and arrays."
  (or (seq-reduce (lambda (acc key)
                    (when (map-p acc)
                      (map-elt acc key)))
                  keys
                  map)
      default))

(defun map-keys (map)
  "Return the list of keys in MAP."
  (map-apply (lambda (key _) key) map))

(defun map-values (map)
  "Return the list of values in MAP."
  (map-apply (lambda (_ value) value) map))

(defun map-pairs (map)
  "Return the elements of MAP as key/value association lists."
  (map-apply (lambda (key value)
               (cons key value))
             map))

(defun map-length (map)
  "Return the length of MAP."
  (length (map-keys map)))

(defun map-copy (map)
  "Return a copy of MAP."
  (map--dispatch map
    :list (seq-copy map)
    :hash-table (copy-hash-table map)
    :array (seq-copy map)))

(defun map-apply (function map)
  "Return the result of applying FUNCTION to each element of MAP.
FUNCTION is called with two arguments, the key and the value."
  (funcall (map--dispatch map
             :list #'map--apply-alist
             :hash-table #'map--apply-hash-table
             :array #'map--apply-array)
           function
           map))

(defun map-keys-apply (function map)
  "Return the result of applying FUNCTION to each key of MAP."
  (map-apply (lambda (key _)
               (funcall function key))
             map))

(defun map-values-apply (function map)
  "Return the result of applying FUNCTION to each value of MAP."
  (map-apply (lambda (_ val)
               (funcall function val))
             map))

(defun map-filter (pred map)
  "Return an alist of the key/val pairs of which (PRED key val) is non-nil in MAP."
  (delq nil (map-apply (lambda (key val)
                         (if (funcall pred key val)
                             (cons key val)
                           nil))
                       map)))

(defun map-remove (pred map)
  "Return an alist of the key/val pairs of which (PRED key val) is nil in MAP."
  (map-filter (lambda (key val) (not (funcall pred key val)))
              map))

(defun map-p (map)
  "Return non-nil if MAP is a map (list, hash-table or array)."
  (or (listp map)
      (hash-table-p map)
      (arrayp map)))

(defun map-empty-p (map)
  "Return non-nil is MAP is empty.
MAP can be a list, hash-table or array."
  (null (map-keys map)))

(defun map-contains-key-p (map key &optional testfn)
  "Return non-nil if MAP contain the key KEY, nil otherwise.
Equality is defined by TESTFN if non-nil or by `equal' if nil.
MAP can be a list, hash-table or array."
  (seq-contains-p (map-keys map) key testfn))

(defun map-some-p (pred map)
  "Return any key/value pair for which (PRED key val) is non-nil is MAP."
  (catch 'map--break
    (map-apply (lambda (key value)
                 (when (funcall pred key value)
                   (throw 'map--break (cons key value))))
               map)
    nil))

(defun map-every-p (pred map)
  "Return non-nil if (PRED key val) is non-nil for all elements of the map MAP."
  (catch 'map--break
    (map-apply (lambda (key value)
                 (or (funcall pred key value)
                     (throw 'map--break nil)))
               map)
    t))

(defun map-merge (type &rest maps)
  "Merge into a map of type TYPE all the key/value pairs in the maps MAPS."
  (let (result)
    (while maps
      (map-apply (lambda (key value)
                   (map-put result key value))
                 (pop maps)))
    (map-into result type)))

(defun map-into (map type)
  "Convert the map MAP into a map of type TYPE.
TYPE can be one of the following symbols: list or hash-table."
  (pcase type
    (`list (map-pairs map))
    (`hash-table (map--into-hash-table map))
    (t (error "Not a map type name: %S" type))))

(defmacro map--dispatch (spec &rest args)
  "Evaluate one of the provided forms depending on the type of MAP.

SPEC can be a map or a list of the form (VAR MAP [RESULT]).
ARGS should have the form [TYPE FORM]...

The following keyword types are meaningful: `:list',
`:hash-table' and `array'.

An error is thrown if MAP is neither a list, hash-table nor array.

Return RESULT if non-nil or the result of evaluation of the
form.

\(fn (VAR MAP [RESULT]) &rest ARGS)"
  (declare (debug t) (indent 1))
  (unless (listp spec)
    (setq spec `(,spec ,spec)))
  (let ((map-var (car spec))
        (result-var (make-symbol "result")))
    `(let ((,map-var ,(cadr spec))
           ,result-var)
       (setq ,result-var
             (cond ((listp ,map-var) ,(plist-get args :list))
                   ((hash-table-p ,map-var) ,(plist-get args :hash-table))
                   ((arrayp ,map-var) ,(plist-get args :array))
                   (t (error "Unsupported map: %s" ,map-var))))
       ,@(when (cddr spec)
          `((setq ,result-var ,@(cddr spec))))
       ,result-var)))

(defun map--apply-alist (function map)
  "Private function used to apply FUNCTION over MAP, MAP being an alist."
  (seq-map (lambda (pair)
             (funcall function
                      (car pair)
                      (cdr pair)))
           map))

(defun map--apply-hash-table (function map)
  "Private function used to apply FUNCTION over MAP, MAP being a hash-table."
  (let (result)
    (maphash (lambda (key value)
               (push (funcall function key value) result))
             map)
    (nreverse result)))

(defun map--apply-array (function map)
  "Private function used to apply FUNCTION over MAP, MAP being an array."
   (let ((index 0))
     (seq-map (lambda (elt)
                (prog1
                    (funcall function index elt)
                  (setq index (1+ index))))
              map)))

(defun map--elt-array (map key &optional default)
  "Return the element of the arary MAP at the index KEY, or DEFAULT if nil."
  (let ((len (seq-length map)))
    (or (and (>= key 0)
             (<= key len)
             (seq-elt map key))
        default)))

(defun map--delete-alist (map key)
  "Return MAP with KEY removed."
  (seq-remove (lambda (pair)
                (equal key (car pair)))
              map))

(defun map--delete-array (map key)
  "Set nil in the array MAP at the index KEY if present and return MAP."
  (let ((len (seq-length map)))
    (and (>= key 0)
         (<= key len)
         (aset m key nil)))
  map)

(defun map--into-hash-table (map)
  "Convert MAP into a hash-table."
  (let ((ht (make-hash-table :size (map-length map)
                             :test 'equal)))
    (map-apply (lambda (key value)
                 (map-put ht key value))
               map)
    ht))

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