When possible, represent functions in a literal way

Author: yrashk

lib/elixir/lib/binary/inspect.ex

@@ -11,7 +11,7 @@ defprotocol Binary.Inspect do
   printing.
   """
 
-  @only [BitString, List, Tuple, Atom, Number, Any]
+  @only [BitString, List, Tuple, Atom, Number, Function, Any]
 
   def inspect(thing, opts)
 end
@@ -417,6 +417,22 @@ defimpl Binary.Inspect, for: Regex do
   end
 end
 
+defimpl Binary.Inspect, for: Function do
+  @moduledoc """
+  Represents functions, in a literal form, when possible
+  """
+
+  def inspect(thing, _opts) do
+    fun_info = :erlang.fun_info(thing)
+    if fun_info[:type] == :external and
+       fun_info[:env] == [] do
+      "function(#{Kernel.inspect(fun_info[:module])}.#{fun_info[:name]}/#{fun_info[:arity]})"
+    else
+      iolist_to_binary :io_lib.format('~p', [thing])
+    end
+  end
+end
+
 defimpl Binary.Inspect, for: Any do
   @moduledoc """
   For all other terms not implemented, we use the default

lib/elixir/test/elixir/binary/inspect_test.exs

@@ -185,6 +185,26 @@ defmodule Binary.Inspect.ListTest do
   end
 end
 
+defmodule Binary.Inspect.FunctionTest do
+  use ExUnit.Case, async: true
+
+  test :funs do
+    bin = inspect(fn(x) -> x + 1 end)
+    assert '#Fun<' ++ _ = binary_to_list(bin)
+  end
+
+  test :external_elixir do
+    bin = inspect(function(Enum.map/2))
+    assert bin == "function(Enum.map/2)"
+  end
+
+  test :external_erlang do
+    bin = inspect(function(:lists.map/2))
+    assert bin == "function(:lists.map/2)"
+  end
+
+end
+
 defmodule Binary.Inspect.AnyTest do
   use ExUnit.Case, async: true