From 3328a62d42ff3ca62c31366a4cd0cfd38a3ec663 Mon Sep 17 00:00:00 2001
From: Sean Allred <code@seanallred.com>
Date: Thu, 15 Jan 2015 00:01:32 -0500
Subject: Create and implement comparator creation macro

This obsoletes `sx--<'.
---
 sx-question-list.el | 10 +++++-----
 sx.el               | 24 +++++++++++++++++-------
 2 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/sx-question-list.el b/sx-question-list.el
index 1b7fe5a..5909156 100644
--- a/sx-question-list.el
+++ b/sx-question-list.el
@@ -322,11 +322,11 @@ into consideration.
   ;; Add a setter to protect the value.
   :group 'sx-question-list)
 
-(defun sx-question-list--date-more-recent-p (x y)
-  "Non-nil if tabulated-entry X is newer than Y."
-  (sx--<
-   sx-question-list-date-sort-method
-   (car x) (car y) #'>))
+(sx--create-comparator sx-question-list--date-more-recent-p
+  "Non-nil if tabulated-entry A is newer than B."
+  > (lambda (x)
+      (cdr (assoc sx-question-list-date-sort-method
+                  (car x)))))
 
 
 ;;; Keybinds
diff --git a/sx.el b/sx.el
index e080271..87907de 100644
--- a/sx.el
+++ b/sx.el
@@ -259,6 +259,23 @@ whenever BODY evaluates to nil."
        :filter (lambda (&optional _)
                  (when (progn ,@body) ,def)))))
 
+(defmacro sx--create-comparator (name doc compare-func get-func)
+  "Define a new comparator called NAME with documentation DOC.
+COMPARE-FUNC is a function that takes the return value of
+GET-FUNC and performs the actual comparison."
+  (declare (indent 1) (doc-string 2))
+  (let ((gpf (intern (format " %S--get-prop-function" name)))
+        (cf  (intern (format " %S--compare-function"  name))))
+    ;; Leading space to hide from completion systems
+    `(progn
+       ;; In using `defalias', the macro supports both function
+       ;; symbols and lambda expressions.
+       (defalias ',gpf ,get-func)
+       (defalias ',cf  ,compare-func)
+       (defun ,name (a b)
+         ,doc
+         (,cf (,gpf a) (,gpf b))))))
+
 
 ;;; Printing request data
 (defvar sx--overlays nil
@@ -349,13 +366,6 @@ Run after `sx-init--internal-hook'."
 This is used internally to set initial values for variables such
 as filters.")
 
-(defun sx--< (property x y &optional predicate)
-  "Non-nil if PROPERTY attribute of alist X is less than that of Y.
-With optional argument PREDICATE, use it instead of `<'."
-  (funcall (or predicate #'<)
-           (cdr (assoc property x))
-           (cdr (assoc property y))))
-
 (defmacro sx-init-variable (variable value &optional setter)
   "Set VARIABLE to VALUE using SETTER.
 SETTER should be a function of two arguments.  If SETTER is nil,
-- 
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