Create and implement comparator creation macro

This obsoletes `sx--<'.

1 files changed, 17 insertions, 7 deletions

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,