while loops can now be used as expressions -- they return an array containing the computed result of each iteration.

examples/documents.coffee

@@ -15,8 +15,8 @@ dc.model.Document: dc.Model.extend({
   # document by binding to Metadata, instead of on-the-fly.
   metadata: =>
     docId: this.id
-    _.select(Metadata.models(), (meta => 
-      _.any(meta.get('instances'), instance => 
+    _.select(Metadata.models(), (meta =>
+      _.any(meta.get('instances'), instance =>
         instance.document_id is docId)))
 
   bookmark: pageNumber =>
@@ -60,7 +60,7 @@ dc.model.DocumentSet: dc.model.RESTfulSet.extend({
   # change their selected state.
   _onModelEvent: e, model =>
     this.base(e, model)
-    fire: e == dc.Model.CHANGED and model.hasChanged('selected')
+    fire: e is dc.Model.CHANGED and model.hasChanged('selected')
     if fire then _.defer(_(this.fire).bind(this, this.SELECTION_CHANGED, this))
 
 })

lib/coffee_script/grammar.y

@@ -353,6 +353,7 @@ rule
   While:
     WHILE Expression Block            { result = WhileNode.new(val[1], val[2]) }
   | WHILE Expression                  { result = WhileNode.new(val[1], nil) }
+  | Expression WHILE Expression       { result = WhileNode.new(val[2], Expressions.wrap(val[0])) }
   ;
 
   # Array comprehensions, including guard and current index.

lib/coffee_script/nodes.rb

@@ -36,9 +36,9 @@ module CoffeeScript
     def compile(o={})
       @options = o.dup
       @indent  = o[:indent]
-      top = self.is_a?(ForNode) ? @options[:top] : @options.delete(:top)
-      closure = statement? && !statement_only? && !top && !@options[:return]
-      closure ? compile_closure(@options) : compile_node(@options)
+      top      = self.top_sensitive? ? @options[:top] : @options.delete(:top)
+      closure  = statement? && !statement_only? && !top && !@options[:return]
+      closure  ? compile_closure(@options) : compile_node(@options)
     end
 
     def compile_closure(o={})
@@ -56,6 +56,7 @@ module CoffeeScript
     def unwrap;           self;   end
     def statement?;       false;  end
     def statement_only?;  false;  end
+    def top_sensitive?;   false;  end
   end
 
   # A collection of nodes, each one representing an expression.
@@ -668,14 +669,27 @@ module CoffeeScript
       @condition, @body = condition, body
     end
 
+    def top_sensitive?
+      true
+    end
+
     def compile_node(o)
       returns     = o.delete(:return)
+      top         = o.delete(:top) && !returns
       o[:indent]  = idt(1)
       o[:top]     = true
       cond        = @condition.compile(o)
-      post        = returns ? "\n#{idt}return null;" : ''
-      return write("#{idt}while (#{cond}) null;#{post}") if @body.nil?
-      write("#{idt}while (#{cond}) {\n#{@body.compile(o)}\n#{idt}}#{post}")
+      set         = ''
+      if !top
+        rvar      = o[:scope].free_variable
+        set       = "#{idt}#{rvar} = [];\n"
+        @body = Expressions.wrap(CallNode.new(
+          ValueNode.new(LiteralNode.new(rvar), [AccessorNode.new('push')]), [@body.unwrap]
+        ))
+      end
+      post        = returns ? "\n#{idt}return #{rvar};" : ''
+      return write("#{set}#{idt}while (#{cond}) null;#{post}") if @body.nil?
+      write("#{set}#{idt}while (#{cond}) {\n#{@body.compile(o)}\n#{idt}}#{post}")
     end
   end
 
@@ -697,6 +711,10 @@ module CoffeeScript
       @name, @index = @index, @name if @object
     end
 
+    def top_sensitive?
+      true
+    end
+
     def compile_node(o)
       top_level     = o.delete(:top) && !o[:return]
       range         = @source.is_a?(ValueNode) && @source.base.is_a?(RangeNode) && @source.properties.empty?

test/fixtures/execution/test_everything.coffee

@@ -26,4 +26,4 @@ func: =>
 
   c.single: c.list[1..1][0]
 
-print(func() == '-')
+print(func() is '-')

test/fixtures/execution/test_while.coffee

@@ -0,0 +1,17 @@
+i: 100
+while i -= 1
+
+print(i is 0)
+
+
+i: 5
+list: while i -= 1
+  i * 2
+
+print(list.join(' ') is "8 6 4 2")
+
+
+i: 5
+list: (i * 3 while i -= 1)
+
+print(list.join(' ') is "12 9 6 3")