Welcome to Scala version 2.10.3 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_25).
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scala> val map0 = Map.empty[Int, Int] withDefaultValue 0
map0: scala.collection.immutable.Map[Int,Int] = Map()

scala> val map1 = map0 mapValues(identity)
map1: scala.collection.immutable.Map[Int,Int] = Map()

scala> map1(1)
java.util.NoSuchElementException: key not found: 1
	at scala.collection.MapLike$class.default(MapLike.scala:228)
	at scala.collection.AbstractMap.default(Map.scala:58)
	at scala.collection.MapLike$class.apply(MapLike.scala:141)
	at scala.collection.AbstractMap.apply(Map.scala:58)
	at .<init>(<console>:10)
	at .<clinit>(<console>)
	at .<init>(<console>:7)
	at .<clinit>(<console>)
	at $print(<console>)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:734)
	at scala.tools.nsc.interpreter.IMain$Request.loadAndRun(IMain.scala:983)
	at scala.tools.nsc.interpreter.IMain.loadAndRunReq$1(IMain.scala:573)
	at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:604)
	at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:568)
	at scala.tools.nsc.interpreter.ILoop.reallyInterpret$1(ILoop.scala:756)
	at scala.tools.nsc.interpreter.ILoop.interpretStartingWith(ILoop.scala:801)
	at scala.tools.nsc.interpreter.ILoop.command(ILoop.scala:713)
	at scala.tools.nsc.interpreter.ILoop.processLine$1(ILoop.scala:577)
	at scala.tools.nsc.interpreter.ILoop.innerLoop$1(ILoop.scala:584)
	at scala.tools.nsc.interpreter.ILoop.loop(ILoop.scala:587)
	at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply$mcZ$sp(ILoop.scala:878)
	at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:833)
	at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:833)
	at scala.tools.nsc.util.ScalaClassLoader$.savingContextLoader(ScalaClassLoader.scala:135)
	at scala.tools.nsc.interpreter.ILoop.process(ILoop.scala:833)
	at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:83)
	at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:96)
	at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:105)
	at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)