From 6af5e4b82e9d2f025ad388f82495865a195c5218 Mon Sep 17 00:00:00 2001
From: William Carroll <wpcarro@gmail.com>
Date: Fri, 11 Dec 2020 22:42:55 +0000
Subject: [PATCH] Define Extras module

I'll use as the host for utility functions needed to extend the stdlib.
---
 assessments/semiprimes/server/lib/extras.ex    | 18 ++++++++++++++++++
 .../semiprimes/server/test/extras_test.exs     | 18 ++++++++++++++++++
 2 files changed, 36 insertions(+)
 create mode 100644 assessments/semiprimes/server/lib/extras.ex
 create mode 100644 assessments/semiprimes/server/test/extras_test.exs

diff --git a/assessments/semiprimes/server/lib/extras.ex b/assessments/semiprimes/server/lib/extras.ex
new file mode 100644
index 000000000..4d2a938fc
--- /dev/null
+++ b/assessments/semiprimes/server/lib/extras.ex
@@ -0,0 +1,18 @@
+defmodule Extras do
+  @doc """
+  Return an ascending range starting at `a` and ending at `b` (exclusive).
+
+  ## Examples
+
+      iex> Extras.range(2, 5)
+      [2, 3, 4]
+
+  """
+  def range(a, b) do
+    if b <= a do
+      []
+    else
+      [a] ++ range(a + 1, b)
+    end
+  end
+end
diff --git a/assessments/semiprimes/server/test/extras_test.exs b/assessments/semiprimes/server/test/extras_test.exs
new file mode 100644
index 000000000..67d0b8875
--- /dev/null
+++ b/assessments/semiprimes/server/test/extras_test.exs
@@ -0,0 +1,18 @@
+defmodule ExtrasTest do
+  use ExUnit.Case
+  doctest Extras
+
+  describe "range" do
+    test "returns an empty list for descending sequences" do
+      assert Extras.range(0, -2) == []
+    end
+
+    test "returns an empty list for non-ascending sequences" do
+      assert Extras.range(8, 8) == []
+    end
+
+    test "returns an exclusive range" do
+      assert Extras.range(3, 6) == [3, 4, 5]
+    end
+  end
+end