From bc5a61ea07ec0f52994e1fb6b4dc24e1580571d6 Mon Sep 17 00:00:00 2001
From: Shannon Oram <shannon.oram@gmail.com>
Date: Sat, 11 Aug 2018 11:18:24 +1000
Subject: [PATCH] Add new koans for comprehensions

Added to partially complete the "Koans for special forms" issue.
https://github.com/elixirkoans/elixir-koans/issues/53
---
 lib/koans/20_comprehensions.ex           | 36 ++++++++++++++++++++++++
 test/koans/comprehensions_koans_test.exs | 18 ++++++++++++
 2 files changed, 54 insertions(+)
 create mode 100644 lib/koans/20_comprehensions.ex
 create mode 100644 test/koans/comprehensions_koans_test.exs

diff --git a/lib/koans/20_comprehensions.ex b/lib/koans/20_comprehensions.ex
new file mode 100644
index 0000000..5f441df
--- /dev/null
+++ b/lib/koans/20_comprehensions.ex
@@ -0,0 +1,36 @@
+defmodule Comprehensions do
+  use Koans
+
+  @intro "Comprehensions"
+
+  # A comprehension is made of three parts: generators, filters and collectables.
+
+  koan "Generators provide the values to be used in a comprehension" do
+    # In the expression below, `n <- [1, 2, 3, 4]` is the generator.
+    assert (for n <- [1, 2, 3, 4], do: n * n) == ___
+  end
+
+  koan "Any enumerable can be a generator" do
+    assert (for n <- 1..4, do: n * n) == ___
+  end
+
+  koan "A generator specifies how to extract values from a collection" do
+    collection = [["Hello","World"], ["Apple", "Pie"]]
+    assert (for [a, b] <- collection, do: "#{a} #{b}") == ___
+  end
+
+  koan "You can use multiple generators at once" do
+    assert (for x <- [2, 4], y <- ["dogs", "cats"], do: "#{x} #{y}") == ___
+  end
+
+  koan "Use a filter to reduce your work" do
+    assert (for n <- [1, 2, 3, 4, 5, 6], n > 3, do: n) == ___
+  end
+
+  koan "Add the result of a comprehension to an existing collection" do
+    pies = ["Apple Pie"]
+    pies = for x <- ["Pecan", "Pumpkin"], into: pies, do: "#{x} Pie"
+    assert pies == ___
+  end
+
+end
diff --git a/test/koans/comprehensions_koans_test.exs b/test/koans/comprehensions_koans_test.exs
new file mode 100644
index 0000000..f162af8
--- /dev/null
+++ b/test/koans/comprehensions_koans_test.exs
@@ -0,0 +1,18 @@
+defmodule ComprehensionsTests do
+  use ExUnit.Case
+  import TestHarness
+
+  test "Comprehensions" do
+    answers = [
+      [1, 4, 9, 16],
+      [1, 4, 9, 16],
+      ["Hello World", "Apple Pie"],
+      ["2 dogs", "2 cats", "4 dogs", "4 cats"],
+      [4, 5, 6],
+      ["Apple Pie", "Pecan Pie", "Pumpkin Pie"],
+    ]
+
+    test_all(Comprehensions, answers)
+  end
+
+end