From bbf3d201c79645760609068a2a3b0da4301227f0 Mon Sep 17 00:00:00 2001
From: fabien townsend <fabientownsend@gmail.com>
Date: Thu, 30 Mar 2017 20:27:47 +0100
Subject: [PATCH] Add read from a streams koans

---
 lib/koans/19_streams.ex           | 27 +++++++++++++++++++++++++++
 lib/runner.ex                     |  1 +
 test/koans/streams_koans_test.exs | 14 ++++++++++++++
 3 files changed, 42 insertions(+)
 create mode 100644 lib/koans/19_streams.ex
 create mode 100644 test/koans/streams_koans_test.exs

diff --git a/lib/koans/19_streams.ex b/lib/koans/19_streams.ex
new file mode 100644
index 00000000..e6c02a31
--- /dev/null
+++ b/lib/koans/19_streams.ex
@@ -0,0 +1,27 @@
+defmodule Streams do
+  use Koans
+
+  @intro "Streams"
+
+  koan "Streams are lazier than Enum, they only return a struct" do
+    assert Stream.map([1, 2, 3], &(&1 + 1)).__struct__ == ___
+  end
+
+  koan "You have to ask it explicitly to do the operation" do
+    updated_list =
+      [1, 2, 3]
+      |> Stream.map(&(&1 + 1))
+      |> Enum.to_list
+
+    assert updated_list == ___
+  end
+
+  koan "Which will let you decide which element you want to compute in the stream" do
+    computed_element =
+      1..42
+      |> Stream.map(&("I computed: #{&1}"))
+      |> Enum.take(1)
+
+    assert computed_element == ___
+  end
+end
diff --git a/lib/runner.ex b/lib/runner.ex
index ac87ae5d..f96e46a7 100644
--- a/lib/runner.ex
+++ b/lib/runner.ex
@@ -18,6 +18,7 @@ defmodule Runner do
     Tasks,
     Agents,
     Protocols,
+    Streams,
   ]
 
   def koan?(koan), do: Enum.member?(@modules, koan)
diff --git a/test/koans/streams_koans_test.exs b/test/koans/streams_koans_test.exs
new file mode 100644
index 00000000..713e11f7
--- /dev/null
+++ b/test/koans/streams_koans_test.exs
@@ -0,0 +1,14 @@
+defmodule StreamsTests do
+  use ExUnit.Case
+  import TestHarness
+
+  test "Streams" do
+    answers = [
+      Stream,
+      [2, 3, 4],
+      ["I computed: 1"],
+    ]
+
+    test_all(Streams, answers)
+  end
+end