Exercise 2.54

Author: Ben Schmeckpeper

exercise_2.54.exs

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+defmodule Equality do
+  def equal?([], []), do: true
+  def equal?([head1 | tail1], [head2 | tail2]), do: equal?(head1, head2) && equal?(tail1, tail2)
+  def equal?(a, b) when is_atom(a) and is_atom(b), do: a == b
+  def equal?(_, _), do: false
+end
+
+ExUnit.start
+
+defmodule EqualityTests do
+  use ExUnit.Case, async: true
+
+  test "empty lists are equal" do
+    assert Equality.equal?([], [])
+  end
+
+  test "single element lists are equal if the elements are equal" do
+    assert Equality.equal?([:a], [:a])
+    refute Equality.equal?([:a], [:b])
+  end
+
+  test "lists of unequal length are not equal" do
+    refute Equality.equal?(~w(foo bar baz bat)a, ~w(foo bar baz)a)
+    refute Equality.equal?(~w(foo bar baz bat)a, ~w(foo bar baz bat qux)a)
+  end
+
+  test "lists of equal length with matching elements are equal" do
+    assert Equality.equal?(~w(foo bar baz bat qux)a, ~w(foo bar baz bat qux)a)
+  end
+end