Improve enum koans

lib/koans/10_enums.ex

@@ -5,60 +5,33 @@ defmodule Enums do
     assert Enum.count([1,2,3]) == :__
   end
 
-  koan "The same applies for counting elements in a map" do
+  koan "Depending on the type, it counts pairs" do
     assert Enum.count(%{ :a => :foo, :b => :bar}) == :__
   end
 
-  koan "Or a keyword list" do
-    assert Enum.count([a: 77, b: 23, c: 12, d: 33, e: 90, f: 113]) == :__
-  end
-
   def less_than_five?(n), do: n < 5
   koan "Elements can have a lot in common" do
     assert Enum.all?([1,2,3], &less_than_five?/1) == :__
-  end
-
-  def less_than_two?(n), do: n < 2
-  koan "If one if different, all elements are not alike" do
-    assert Enum.all?([1, 2, 3, 2], &less_than_two?/1) == :__
+    assert Enum.all?([6,7,8,9], &less_than_five?/1) == :__
   end
 
   def even?(n), do: rem(n, 2) == 0
-
   koan "sometimes you you just want to know if there are any elements fullfilling a condition" do
     assert Enum.any?([1,2,3], &even?/1) == :__
-  end
-
-  def  divisible_by_five?(n), do: rem(n, 5) == 0
-
-  koan "if not a single element fits the bill, any? returns false" do
-    assert Enum.any?([1,2,3], &divisible_by_five?/1) == :__
+    assert Enum.any?([1,3,5], &even?/1) == :__
   end
 
   koan "Sometimes you just want to know if an element is part of the party" do
-    assert Enum.member?([1,2,3], 1) == :__
-  end
-
-  koan "And sometimes your invited guests don't show up and miss the party" do
-    assert Enum.member?([1,2,3], 30) == :__
+    input = [1,2,3]
+    assert Enum.member?(input, 1) == :__
+    assert Enum.member?(input, 30) == :__
   end
 
   def multiply_by_ten(n), do: 10 * n
-
   koan "map converts each element of a list by running some function with it" do
     assert Enum.map([1,2,3], &multiply_by_ten/1) == :__
   end
 
-  koan "You can even return a list with entirely different types" do
-    assert Enum.map([1,2,3], &even?/1) == :__
-  end
-
-  koan "But keep in mind that the original list remains unchanged" do
-    input = [1,2,3,4]
-    assert Enum.map(input, &even?/1) == :__
-    assert input == :__
-  end
-
   def odd?(n), do: rem(n, 2) == 1
 
   koan "Filter allows you to only keep what you really care about" do
@@ -77,45 +50,21 @@ defmodule Enums do
     assert Enum.take([1,2,3,4,5], 10) == :__
   end
 
-  koan "Take what you can..." do
-    assert Enum.take_while([1,2,3,4,5,6,7], &less_than_five?/1) == :__
-  end
-
   koan "Just like taking, you can also drop elements" do
     assert Enum.drop([-1,0,1,2,3], 2) == :__
   end
 
-  def negative?(n), do: n < 0
-  koan "Drop elements until you are happy" do
-    assert Enum.drop_while([-1,0,1,2,3], &negative?/1) == :__
-  end
-
-  koan "Forming groups makes uns stronger" do
-    odd_or_even = fn element -> if rem(element, 2) == 0 do :even else :odd end end
-
-    assert Enum.group_by([1,2,3,4], odd_or_even) == :__
-  end
-
-  koan "You get as many groups as you can have different results" do
-    assert Enum.group_by([1,2,3,4,5,6], fn element -> rem(element, 3) end) == :__
-  end
-
   koan "Zip-up in pairs!" do
     numbers = [1,2,3]
     letters = [:a, :b, :c]
     assert Enum.zip(numbers, letters) == :__
   end
 
- koan "Sorry, but if you don't have a pair you are left out" do
-    more_numbers = [1,2,3] ++ [4,5]
-    letters = [:a, :b, :c]
-    assert Enum.zip(more_numbers, letters) == :__
-  end
-
   koan "When you want to find that one pesky element" do
     assert Enum.find([1,2,3], &even?/1) == :__
   end
 
+  def divisible_by_five?(n), do: rem(n, 5) == 0
   koan "...but you don't quite find it..." do
     assert Enum.find([1,2,3], &divisible_by_five?/1) == :__
   end