fix readme

README.md

@@ -8,7 +8,11 @@ Solutions for each chapter is a submodule in this project.
 
 Common code may be put into the `common` submodule.
 
-Files under `worksheets/` may be arbitrary Scala code, not made into a test. SBT will ignore those files.
+Files under `worksheets/` may be arbitrary Scala code, not made into a test.
+
+## Verifying worksheets
+
+Run the command `bash run_sbt.sh test` in order to verify all solutions. This will create temporary solution files in each chapter.
 
 # Code formatting
 

chapter02/worksheets/solution2.1.7.3_AR.scala

@@ -5,7 +5,8 @@ Given two sequences p: Seq[String] and q: Seq[Boolean] of equal length, compute
 Seq[String] with those elements of p for which the corresponding element of q is true.
 Hint: use zip, map, filter. */ 
 
-Seq("Joe", "Bob", "Mary").zip(Seq(true, false, true)).map { case (x, y) => if (y == true) x }.filter(_ != (())).map{ case x => x.toString }
+val result = Seq("Joe", "Bob", "Mary").zip(Seq(true, false, true)).map { case (x, y) => if (y == true) x }.filter(_ != (())).map{ case x => x.toString }
+assert(result == List("Joe", "Mary"))
 
 // scala> :load solution2.1.7.3_AR.scala
 // Loading solution2.1.7.3_AR.scala...