Add logic to exclude some pages based on some tags

docs/_includes/custom/shuffle_panel.html

@@ -1,13 +1,23 @@
 <!-- Argument summary: -->
 
-<!-- tags: tag determining the pages included in the panel -->
+<!-- tags: comma-separated tags determining the pages included in the panel -->
+<!-- except_tags: comma-separated tags to filter out some pages -->
+
+<!-- A page is included if it has all the include tags and none of the exclude tags -->
+
+
 <!-- title: Display title of the panel -->
 <!-- description: Description of the panel -->
+<!-- datagroups: json array containing the data groups for the shuffle logic -->
+
 <!-- image (optional) : Name of the image to use, as a css class, eg "fa-list" -->
 <!-- titlemaker (optional) : name of a variable that's evaluated to determine the displayed title of the page. Default is page.title -->
 
 
 {% capture titlemaker %} {{ include.titlemaker | default: "page.title" }} {% endcapture %}
+{% assign include_tags = {{ include.tags | split: "," }} %}
+{% assign exclude_tags = {{ include.except_tags | split: "," }} %}
+
 
 <div class="col-xs-6 col-sm-4 col-md-4" data-groups='{{ include.datagroups }}'>
     <div class="panel panel-default">
@@ -30,9 +40,10 @@
             </p>
             <ul>
                 {% for page in site.pages %}
-                    {% capture alltags %}{{ page.tags | contains_all: include.tags }}{% endcapture %}
-                    <!-- ugly, but one can only capture string values -->
-                    {% if alltags contains "true" %}
+                    {% capture included %}{{ page.tags | intersect: include_tags | equals: include_tags }}{% endcapture %}
+                    {% capture excluded %}{{ page.tags | intersect: exclude_tags | empty }}{% endcapture %}
+
+                    {% if included contains "true" and excluded contains "true" %}
                         <li><a href="{{page.url | remove: '/'}}">{% eval titlemaker %}</a></li>
                     {% endif %}
                 {% endfor %}

docs/_plugins/custom_filters.rb

@@ -1,27 +1,24 @@
 module CustomFilters
 
-  def contains_all(input, test)
-    if !test
-      !input
-    elsif !input
-      false
+  def intersect(xs, ys)
+    if !xs || !ys
+      []
     else
-      test.split(",").all? {|val| input.include?(val)}
-
+      Array(xs) & Array(ys)
     end
   end
 
-  def intersect(xs, ys)
-    xs & ys
+  def equals(xs, ys)
+    a = Array(xs)
+    b = Array(ys)
+
+    ((a | b) - (a & b)).empty?
   end
 
-  def union(xs, ys)
-    xs | ys
+  def empty(xs)
+    Array(xs).empty?
   end
 
-  def diff(xs, ys)
-    xs - ys
-  end
 end
 
 Liquid::Template.register_filter(CustomFilters)

docs/_plugins/eval_tag.rb

@@ -1,6 +1,5 @@
 
-# This tag takes a variable name as an input, and evaluates its value twice
-# (follows one indirection)
+# This tag takes a variable name as an input, and evaluates its value twice (dereferences it once)
 # E.g. if the symbol table is E = {"foo" => "bar", "bar" => "baz"},
 # then {% eval foo %} ~> E[E["foo"]] ~> E["bar"] ~> "baz"