Merge pull request #225 from s-oram/special_forms

Add new koans for comprehensions

lib/koans/20_comprehensions.ex

@@ -0,0 +1,33 @@
+defmodule Comprehensions do
+  use Koans
+
+  @intro "A comprehension is made of three parts: generators, filters, and collectibles. We will look at how these interact with eachother"
+
+  koan "The generator, `n <- [1, 2, 3, 4]`, is providing the values for our comprehension" do
+    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 <- ["little", "big"], 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
+    collection = ["Apple Pie"]
+    collection = for x <- ["Pecan", "Pumpkin"], into: collection, do: "#{x} Pie"
+    assert collection == ___
+  end
+
+end

test/koans/comprehensions_koans_test.exs

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+defmodule ComprehensionsTests do
+  use ExUnit.Case
+  import TestHarness
+
+  test "Comprehensions" do
+    answers = [
+      [1, 4, 9, 16],
+      [1, 4, 9, 16],
+      ["Hello World", "Apple Pie"],
+      ["little dogs", "little cats", "big dogs", "big cats"],
+      [4, 5, 6],
+      ["Apple Pie", "Pecan Pie", "Pumpkin Pie"],
+    ]
+
+    test_all(Comprehensions, answers)
+  end
+
+end