class Map

  def initialize(window, mapfile)
    @window = window
    @tileset = Gosu::Image.load_tiles(window, 'media/32x32diagonal_lines.png',
                                      32, 32, false)
  end

  def get_lines(file)
    @lines = File.readlines(file).map { |line| line.chomp }
  end

end

class Map

	def initialize(window, mapfile)
		@window = window
		@tileset = Gosu::Image.load_tiles(window, 'media/32x32diagonal_lines.png',
		                                  32, 32, false)
	end

end

--- 
+++ 
@@ -1,9 +1,13 @@
 class Map
 
-	def initialize(window, mapfile)
-		@window = window
-		@tileset = Gosu::Image.load_tiles(window, 'media/32x32diagonal_lines.png',
-		                                  32, 32, false)
-	end
+  def initialize(window, mapfile)
+    @window = window
+    @tileset = Gosu::Image.load_tiles(window, 'media/32x32diagonal_lines.png',
+                                      32, 32, false)
+  end
+
+  def get_lines(file)
+    @lines = File.readlines(file).map { |line| line.chomp }
+  end
 
 end
Create get_lines method, covert tabs to spaces
