Blocks within for-comprehensions

In another example of uniformity it is possible to use blocks within a for-comprehension when creating a generator or making an assignment. The basic form of a for-comprehension is

1. for {i <- generator 
2.      if guard
3.      j = assignment } yield result

The generator, guard, assignment and result are all expressions which means they can all be blocks or simple statements. Most commonly you will see them as simple statements:

1. scala> for {i <- 1 to 10
2.      |      if i % 2 == 0
3.      |      j = i } yield j
4. res50: scala.collection.immutable.IndexedSeq[Int] = IndexedSeq(2, 4, 6, 8, 10)

But since they are expressions they can be more complex:

1. scala> for {  
2.      |  i <- { 
3.      |     val start = nextInt(3)
4.      |     val end = nextInt(10)+start
5.      |     start to end
6.      |  }
7.      |  if {
8.      |    val cut = nextInt(3)+1
9.      |    i % cut == 0
10.      |  }
11.      |  j = {
12.      |    val x = i+1
13.      |    x / 2
14.      |  }
15.      |  }  yield {
16.      |    // do a debug println
17.      |    println(j)
18.      |  j
19.      |  }
20. 1
21. 1
22. 2
23. 3
24. res53: scala.collection.immutable.IndexedSeq[Int] = IndexedSeq(1, 1, 2, 3)