Merge pull request scala#863 from lierdakil/sequence-comp

Remove old "sequence comprehensions" in tour

Author: SethTisue

_tour/for-comprehensions.md

@@ -51,3 +51,16 @@ Here `n == 10` and `v == 10`. On the first iteration, `i == 0` and `j == 0` so `
 
 (0, 0) (0, 1) (0, 2) (0, 3) (0, 4) (0, 5) (0, 6) (0, 7) (0, 8) (0, 9) (1, 1) ...
 ```
+
+Note that comprehensions are not restricted to lists. Every datatype that supports the operations `withFilter`, `map`, and `flatMap` (with the proper types) can be used in sequence comprehensions.
+
+You can omit `yield` in a comprehension. In that case, comprehension will return `Unit`. This can be useful in case you need to perform side-effects. Here's a program equivalent to the previous one, but without using `yield`:
+
+```tut
+def foo(n: Int, v: Int) =
+   for (i <- 0 until n;
+        j <- i until n if i + j == v)
+   print(s"($i, $j)")
+
+foo(10, 10)
+```