Add @while.

lib/sass/engine.rb

@@ -324,6 +324,8 @@ END
         parse_if(line, root, value)
       elsif directive == "for"
         parse_for(line, root, value)
+      elsif directive == "while"
+        parse_while(line, root, value)
       else
         Tree::DirectiveNode.new(line.text, @options)
       end
@@ -366,6 +368,14 @@ END
       tree
     end
 
+    def parse_while(line, root, text)
+      tree = []
+      while Sass::Constant.parse(text, @constants, line.index).to_bool
+        append_children(tree, line.children, root)
+      end
+      tree
+    end
+
     def parse_mixin_definition(line)
       name, args = line.text.scan(/^=\s*([^(]+)(\([^)]*\))?$/).first
       raise SyntaxError.new("Invalid mixin \"#{line.text[1..-1]}\".", @line) if name.nil?

test/sass/engine_test.rb

@@ -491,6 +491,31 @@ CSS
 SASS
   end
 
+  def test_while
+    assert_equal(<<CSS, render(<<SASS))
+a-5 {
+  blooble: gloop; }
+
+a-4 {
+  blooble: gloop; }
+
+a-3 {
+  blooble: gloop; }
+
+a-2 {
+  blooble: gloop; }
+
+a-1 {
+  blooble: gloop; }
+CSS
+!a = 5
+@while !a ~= 0
+  a-\#{!a}
+    blooble: gloop
+  !a = !a - 1
+SASS
+  end
+
   def test_argument_error
     assert_raise(Sass::SyntaxError) { render("a\n  b = hsl(1)") }
   end