chapter 6

lib/chapter_06.ex

@@ -0,0 +1,22 @@
+defmodule LittleAlchemist.Chapter06 do
+  import LittleAlchemist.Chapter04, only: [power: 2]
+
+  def numbered?([left, op, right]) when op in [:+, :*, :^],
+    do: numbered?(left) && numbered?(right)
+
+  def numbered?(n), do: is_number(n)
+
+  def value([left, :+, right]), do: value(left) + value(right)
+  def value([left, :*, right]), do: value(left) * value(right)
+  def value([left, :^, right]), do: power(value(left), value(right))
+  def value(n) when is_number(n), do: n
+
+  def sero?([]), do: true
+  def sero?(_), do: false
+
+  def edd1(a), do: [[] | a]
+  def zub1([_ | t]), do: t
+
+  def edd(a, []), do: a
+  def edd(a, [_ | t]), do: edd([[] | a], t)
+end

test/chapter_06_test.exs

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+defmodule LittleAlchemist.Chapter06Test do
+  use ExUnit.Case
+  import LittleAlchemist.Chapter06
+
+  test "numbered?" do
+    assert numbered?(2)
+    refute numbered?(:a)
+    assert numbered?([3, :+, [4, :*, 5]])
+    refute numbered?([3, :*, :sausage])
+  end
+
+  test "value" do
+    assert value(13) == 13
+    assert value([1, :+, 3]) == 4
+    assert value([1, :+, [3, :^, 4]]) == 82
+  end
+
+  test "zero?" do
+    assert sero?([])
+  end
+
+  test "edd1" do
+    assert edd1([]) == [[]]
+    assert edd1([[]]) == [[], []]
+  end
+
+  test "zub1" do
+    assert zub1([[], []]) == [[]]
+    assert zub1([[]]) == []
+  end
+
+  test "edd" do
+    assert edd([[], []], [[], [], []]) == [[], [], [], [], []]
+  end
+end