Mon Nov 30 04:09:10 UTC 2009  pix@kepibu.org
  * Add :nth-child selector
diff -rN -u old-Oh, Ducks!/notes new-Oh, Ducks!/notes
--- old-Oh, Ducks!/notes	2015-10-10 16:14:29.000000000 +0000
+++ new-Oh, Ducks!/notes	2015-10-10 16:14:29.000000000 +0000
@@ -115,9 +115,9 @@
  * [ ] selectors involving descendants
 ** write documentation
 ** improve selector support
-*** positional selectors [2/12]
+*** positional selectors [3/12]
  * [X] :nth-child(n)
- * [ ] :nth-child(xn+y)
+ * [X] :nth-child(xn+y)
  * [ ] :nth-last-child
  * [X] :first-child
  * [ ] :last-child
diff -rN -u old-Oh, Ducks!/selectors.lisp new-Oh, Ducks!/selectors.lisp
--- old-Oh, Ducks!/selectors.lisp	2015-10-10 16:14:29.000000000 +0000
+++ new-Oh, Ducks!/selectors.lisp	2015-10-10 16:14:29.000000000 +0000
@@ -34,6 +34,7 @@
 (defclass id-selector    (simple-selector) ())
 (defclass class-selector (simple-selector) ())
 (defclass nth-child-selector (simple-selector) ())
+(defclass nth-last-child-selector (nth-child-selector) ())
 
 (defmethod print-object ((selector universal-selector) stream)
   (format stream "#<universal-selector>"))
@@ -53,10 +54,25 @@
     (#T(regexp$ "[ ]+"        ())
      (list (make-instance 'descendant-combinator :matcher (parse-selector &rest))))
     ;; simple selectors
-    (#T(regexp$ ":nth-child\\([ ]*([0-9]+)[ ]*\\)" (?n))
-     (cons (make-instance 'nth-child-selector :arg (parse-integer n)) (parse-selector &rest)))
+    ;; FIXME: fix cl-unification so it can handle non-matching groups,
+    ;;        so we can merge all these nth-child-selector variants
+    ;;        into one or two
+    (#T(regexp$ ":nth-child\\([ ]*([+-]?[0-9]+)n[ ]*([+-]?[0-9]+)[ ]*\\)" (?a ?b))
+     (cons (make-instance 'nth-child-selector :arg (cons (parse-integer a) (parse-integer b))) (parse-selector &rest)))
+    (#T(regexp$ ":nth-child\\([ ]*([+-]?[0-9]+)n[ ]*\\)" (?a))
+     (cons (make-instance 'nth-child-selector :arg (cons (parse-integer a) 0)) (parse-selector &rest)))
+    (#T(regexp$ ":nth-child\\([ ]*n[ ]*([+-]?[0-9]+)[ ]*\\)" (?b))
+     (cons (make-instance 'nth-child-selector :arg (cons 1 (parse-integer b))) (parse-selector &rest)))
+    (#T(regexp$ ":nth-child\\([ ]*-n[ ]*([+-]?[0-9]+)[ ]*\\)" (?b))
+     (cons (make-instance 'nth-child-selector :arg (cons -1 (parse-integer b))) (parse-selector &rest)))
+    (#T(regexp$ ":nth-child\\([ ]*([+-]?[0-9]+)[ ]*\\)" (?b))
+     (cons (make-instance 'nth-child-selector :arg (cons 0 (parse-integer b))) (parse-selector &rest)))
+    (#T(regexp$ ":nth-child\\([ ]*odd[ ]*\\)" ())
+     (cons (make-instance 'nth-child-selector :arg (cons 2 1)) (parse-selector &rest)))
+    (#T(regexp$ ":nth-child\\([ ]*even[ ]*\\)" ())
+     (cons (make-instance 'nth-child-selector :arg (cons 2 0)) (parse-selector &rest)))
     (#T(regexp$ ":first-child" ())
-     (cons (make-instance 'nth-child-selector :arg 1) (parse-selector &rest)))
+     (cons (make-instance 'nth-child-selector :arg (cons 0 1)) (parse-selector &rest)))
     (#T(regexp$ "[#](\\w+)"    (?id))
      (cons (make-instance 'id-selector :arg id)       (parse-selector &rest)))
     (#T(regexp$ "[\\.](\\w+)"  (?class))
@@ -88,8 +104,20 @@
 
 (defmethod element-matches-p (element (selector nth-child-selector))
   (when-let* ((parent (element-parent element))
-              (pos (position element (element-children parent) :test #'eq)))
-    (= (selector-arg selector) (1+ pos))))
+              (pos (position element (funcall (typecase selector
+                                                (nth-last-child-selector #'reverse)
+                                                (nth-child-selector #'identity))
+                                              (element-children parent)) :test #'eq)))
+    (let ((pos (1+ pos))
+          (a (car (selector-arg selector)))
+          (b (cdr (selector-arg selector))))
+      ;; pos = An + B
+      (cond
+        ;; pos = 0n + B
+        ((= 0 a) (= b pos))
+        ;; (pos - B)/A = n
+        (t (and (zerop (mod (- pos b) a))
+                (not (minusp (/ (- pos b) a)))))))))
 
 (defmethod element-matches-p (element (selector class-selector))
   (member (selector-arg selector)