Fix errors with ref/4 IEx helper (#8016)

* Fix errors with ref/4 IEx helper

In addition, include documentation for that function.

* Update helpers.ex

* Add IEx.Helpers.ref/* tests

* Use examples that do not return ArgumentError

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>

lib/iex/lib/iex/helpers.ex

@@ -1204,8 +1204,8 @@ defmodule IEx.Helpers do
 
   ## Examples
 
-      iex> ref("0.21.32.43")
-      #Reference<0.21.32.43>
+      iex> ref("0.1.2.3")
+      #Reference<0.1.2.3>
 
   """
   @doc since: "1.6.0"
@@ -1213,16 +1213,25 @@ defmodule IEx.Helpers do
     :erlang.list_to_ref('#Ref<#{string}>')
   end
 
+  @doc """
+  Creates a Reference from its 4 non-negative integers components.
+
+  ## Examples
+
+      iex> ref(0, 1, 2, 3)
+      #Reference<0.1.2.3>
+
+  """
   @doc since: "1.6.0"
   def ref(w, x, y, z)
       when is_integer(w) and w >= 0 and is_integer(x) and x >= 0 and is_integer(y) and y >= 0 and
              is_integer(z) and z >= 0 do
     :erlang.list_to_ref(
-      '<' ++
+      '#Ref<' ++
         Integer.to_charlist(w) ++
         '.' ++
         Integer.to_charlist(x) ++
-        '.' ++ '.' ++ Integer.to_charlist(y) ++ '.' ++ '.' ++ Integer.to_charlist(z) ++ '.' ++ '>'
+        '.' ++ Integer.to_charlist(y) ++ '.' ++ Integer.to_charlist(z) ++ '>'
     )
   end
 

lib/iex/test/iex/helpers_test.exs

@@ -1090,6 +1090,26 @@ defmodule IEx.HelpersTest do
     end
   end
 
+  describe "ref" do
+    test "builds a ref from string" do
+      assert inspect(ref("0.419006.1377304581.1")) == "#Reference<0.419006.1377304581.1>"
+      assert inspect(ref("0.1.2.3")) == "#Reference<0.1.2.3>"
+
+      assert_raise ArgumentError, fn ->
+        ref("0.6.6.-6")
+      end
+    end
+
+    test "builds a ref from integers" do
+      assert inspect(ref(0, 419_006, 1_377_304_581, 1)) == "#Reference<0.419006.1377304581.1>"
+      assert inspect(ref(0, 1, 2, 3)) == "#Reference<0.1.2.3>"
+
+      assert_raise FunctionClauseError, fn ->
+        ref(0, 6, 6, -6)
+      end
+    end
+  end
+
   describe "i" do
     test "prints information about the data type" do
       assert capture_io(fn -> i(:ok) end) =~ """