some more learnings

concat.exs

···
+defmodule Concat do
+  def join(a, b, sep \\ "")
+
+	def join(a, b, _sep) when b == "" do
+    a
+	end
+
+	def join(a, b, sep) do
+	  a <> sep <> b
+	end
+end
+
+IO.puts(Concat.join("Hello", ""))
+IO.puts(Concat.join("Hello", "world", "-"))
+IO.puts(is_atom(String))

math.exs

···
+defmodule Math do
+  def sum(a, b) do
+    a + b
+  end
+
+  defp multi(a, b) do
+    a * b
+  end
+
+  def zero?(0) do
+    true
+  end
+
+  def zero?(x) when is_integer(x) do
+    false
+  end
+end
+
+IO.puts(Math.sum(1, 2))
+
+IO.puts(Math.zero?(0))
+IO.puts(Math.zero?(1))
+IO.puts(Math.zero?(0.0))

module-nesting.exs

···
+import List, only: [duplicate: 2]
+
+defmodule Foo do
+  defmodule Bar do
+  end
+end
+
+alias Foo.Bar, as: Bar
+
+defmodule Stats do
+	alias Math.List, as: List
+	# alias Math.List
+end
+
+
+defmodule Math do
+	def plus(a, b) do
+    alias Math.List
+	end
+
+	def some_func do
+    import List, only: [duplicate: 2]
+    duplicate(:ok, 2)
+	end
+end