Adding #drop support.

Pretty straightforward.

lib/frappuccino/stream.rb

@@ -12,6 +12,7 @@ class Stream
 require 'frappuccino/stream/map'
 require 'frappuccino/stream/select'
 require 'frappuccino/stream/zip'
+require 'frappuccino/stream/drop'
 
 def not_implemented(m, message)
   define_method m do |*args, &blk|
@@ -60,6 +61,10 @@ def map(&blk)
     end
     alias :collect :map
 
+    def drop(n)
+      Drop.new(self, n)
+    end
+
     def map_stream(hsh)
       Map.new(self) do |event|
         if hsh.has_key?(event)

lib/frappuccino/stream/drop.rb

@@ -0,0 +1,19 @@
+module Frappuccino
+  class Drop < Stream
+    def initialize(source, n)
+      source.add_observer(self)
+
+      @count = 0
+      @dropped = 0
+      @n = n
+    end
+
+    def update(event)
+      @dropped += 1
+
+      if @dropped > @n
+        occur(event)
+      end
+    end
+  end
+end

test/drop_test.rb

@@ -0,0 +1,14 @@
+require 'test_helper'
+
+describe "drop" do
+  it "ignores the first n events" do
+    button = Button.new
+
+    stream = Frappuccino::Stream.new(button)
+    dropped_stream = stream.drop(3)
+
+    5.times { button.push }
+
+    assert_equal 2, dropped_stream.count
+  end
+end