Merge pull request #120 from elixirkoans/improve-pattern-matching

Move pinning to the back of the kaon and enhance example

lib/koans/10_pattern_matching.ex

@@ -7,24 +7,6 @@ defmodule PatternMatching do
     assert match?(1, ___)
   end
 
-  koan "A value can be bound to a variable" do
-    a = 1
-    assert a == ___
-  end
-
-  koan "A variable can be rebound" do
-    a = 1
-    a = 2
-    assert a == ___
-  end
-
-  koan "A variable can be pinned to prevent it from being rebounded" do
-    a = 1
-    assert_raise MatchError, fn() ->
-      ^a = ___
-    end
-  end
-
   koan "Patterns can be used to pull things apart" do
     [head | tail] = [1, 2, 3, 4]
 
@@ -117,4 +99,45 @@ defmodule PatternMatching do
     %{name: name} = %Animal{kind: "dog", name: "Max"}
     assert name == ___
   end
+
+  koan "A value can be bound to a variable" do
+    a = 1
+    assert a == ___
+  end
+
+  koan "A variable can be rebound" do
+    a = 1
+    a = 2
+    assert a == ___
+  end
+
+  koan "A variable can be pinned to use its value when matching instead of binding to a new value" do
+    pinned_variable = 1
+
+    example = fn
+      (^pinned_variable) -> "The number One"
+      (2) -> "The number Two"
+      (number) -> "The number #{number}"
+    end
+    assert example.(1) == ___
+    assert example.(2) == ___
+    assert example.(3) == ___
+  end
+
+  koan "Pinning works anywhere one would match, including 'case'" do
+    pinned_variable = 1
+    result = case 1 do
+               ^pinned_variable -> "same"
+               other -> "different #{other}"
+             end
+
+    assert result == ___
+  end
+
+  koan "Trying to rebind a pinned variable will result in an error" do
+    a = 1
+    assert_raise MatchError, fn() ->
+      ^a = ___
+    end
+  end
 end

test/koans/patterns_koans_test.exs

@@ -5,9 +5,6 @@ defmodule PatternsTests do
   test "Pattern Matching" do
     answers = [
       1,
-      1,
-      2,
-      2,
       {:multiple, [1, [2,3,4]]},
       [1,2,3,4],
       3,
@@ -20,6 +17,11 @@ defmodule PatternsTests do
       "dog",
       "Max",
       "Max",
+      1,
+      2,
+      {:multiple, ["The number One", "The number Two", "The number 3"]},
+      "same",
+      2
     ]
 
     test_all(PatternMatching, answers)