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+;;; 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)
+
+(pcase-defmacro map (&rest args)
+  "pcase pattern matching map elements.
+Matches if the object is a map (list, hash-table or array), and
+binds values from ARGS to the corresponding element of the map.
+
+ARGS can be a list elements of the form (KEY . PAT) or elements
+of the form SYMBOL, which stands for (SYMBOL . SYMBOL)."
+  `(and (pred map-p)
+        ,@(map--make-pcase-bindings args)))
+
+(defmacro map-let (args map &rest body)
+  "Bind the variables in ARGS to the elements of MAP then evaluate BODY.
+
+ARGS can be an alist of key/binding pairs or a list of keys.  MAP
+can be a list, hash-table or array."
+  (declare (indent 2) (debug t))
+  `(pcase-let ((,(map--make-pcase-patterns args) ,map))
+     ,@body))
+
+(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 can be a list, hash-table or array."
+  (map--dispatch map
+    :list (map--elt-list map key 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.
+
+MAP can be a list, hash-table or array."
+  (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.
+
+MAP can be a list, hash-table or array."
+  (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)
+  "Traverse 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 can be a list, hash-table or array."
+  (map-apply (lambda (key _) key) map))
+
+(defun map-values (map)
+  "Return the list of values in MAP.
+
+MAP can be a list, hash-table or array."
+  (map-apply (lambda (_ value) value) map))
+
+(defun map-pairs (map)
+  "Return the elements of MAP as key/value association lists.
+
+MAP can be a list, hash-table or array."
+  (map-apply #'cons map))
+
+(defun map-length (map)
+  "Return the length of MAP.
+
+MAP can be a list, hash-table or array."
+  (length (map-keys map)))
+
+(defun map-copy (map)
+  "Return a copy of MAP.
+
+MAP can be a list, hash-table or array."
+  (map--dispatch map
+    :list (seq-copy map)
+    :hash-table (copy-hash-table map)
+    :array (seq-copy map)))
+
+(defun map-apply (function map)
+  "Apply FUNCTION to each element of MAP and return the result as a list.
+FUNCTION is called with two arguments, the key and the value.
+
+MAP can be a list, hash-table or array."
+  (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 can be a list, hash-table or array."
+  (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 can be a list, hash-table or array."
+  (map-apply (lambda (_ val)
+               (funcall function val))
+             map))
+
+(defun map-filter (pred map)
+  "Return an alist of the key/val pairs for which (PRED key val) is non-nil in MAP.
+
+MAP can be a list, hash-table or array."
+  (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 for which (PRED key val) is nil in MAP.
+
+MAP can be a list, hash-table or array."
+  (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."
+  (map--dispatch map
+    :list (null map)
+    :array (seq-empty-p map)
+    :hash-table (zerop (hash-table-count 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 a key/value pair for which (PRED key val) is non-nil in MAP.
+
+MAP can be a list, hash-table or array."
+  (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.
+
+MAP can be a list, hash-table or array."
+  (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.
+
+MAP can be a list, hash-table or array."
+  (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.
+MAP can be a list, hash-table or array."
+  (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-list (map key &optional default)
+  "Lookup, in the list MAP, the value associated with KEY and return it.
+If KEY is not found, return DEFAULT which defaults to nil."
+  (let ((pair (assoc key map)))
+    (if pair
+        (cdr pair)
+      default)))
+
+(defun map--elt-array (map key &optional default)
+  "Return the element of the array MAP at the index KEY.
+If KEY is not found, return DEFAULT which defaults to 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))
+
+(defun map--make-pcase-bindings (args)
+  "Return a list of pcase bindings from ARGS to the elements of a map."
+  (seq-map (lambda (elt)
+             (if (consp elt)
+                 `(app (pcase--flip map-elt ',(car elt)) ,(cdr elt))
+               `(app (pcase--flip map-elt ',elt) ,elt)))
+           args))
+
+(defun map--make-pcase-patterns (args)
+  "Return a list of `(map ...)' pcase patterns built from ARGS."
+  (cons 'map
+        (seq-map (lambda (elt)
+                   (if (and (consp elt) (eq 'map (car elt)))
+                       (map--make-pcase-patterns elt)
+                     elt))
+                 args)))
+
+(provide 'map)
+;;; map.el ends here