#4 obvious(?) things for elisp

shadchen.el

@@ -1499,8 +1499,31 @@ the matching expression from the body."
 	  (list ,@patterns)))))
 
 
-(provide 'shadchen)
+;; A few obvious EmacsLisp extras
+
+(defun shadchen/extract (key type)
+  "Return a func to extract KEY from TYPE. 
+
+TYPE is either `:alist' or `:plist'."
+  (lambda (kvlist)
+    (case type
+      (:plist (plist-get kvlist key))
+      (:alist (cdr-safe (assoc key kvlist))))))
 
+(defpattern plist (&rest kv-pairs) 
+  `(and ,@(loop for (k v . rest) on kv-pairs by #'cddr
+             collect
+               `(funcall (shadchen/extract ,k :plist) ,v))))
 
+(defpattern alist (&rest kv-pairs)
+  (cl-labels ((alist-get (key)
+                         (lambda (alist)
+                           (cdr (assoc key alist)))))
+    `(and ,@(loop for (k v . rest) on kv-pairs by #'cddr
+               collect
+                 `(funcall (shadchen/extract ,k :alist) ,v)))))
+
+
+(provide 'shadchen)
 
 ;;; shadchen.el ends here

tests.el

@@ -60,4 +60,23 @@
 (setf (symbol-function 'test-product) nil)
 
 (test-product (list 1 2 3))
-(eq (get-recur-sigil-for 'x) (get-recur-sigil-for 'x))
+(eq (get-recur-sigil-for 'x) (get-recur-sigil-for 'x))
+
+
+;; Alists and Plists
+
+(assert
+ (equal
+  (match
+   '(:one 1 :two 2 :three 3)
+   ((plist :two a) a))
+  2)) ; because that's the value of :two in the plist
+
+(assert
+ (equal
+  (match
+   '((a . 1)(b . 2)(c . 3))
+   ((alist 'c a) a))
+  3)) ; because that's the value of 'c in the alist
+
+;;