Add :history_size option to IEx

Author: alco

lib/iex/lib/iex/helpers.ex

@@ -81,7 +81,7 @@ defmodule IEx.Helpers do
   their results.
   """
   def v do
-    history = Enum.reverse(Process.get(:iex_history))
+    history = Enum.reverse(:queue.to_list(Process.get(:iex_history)))
     Enum.each(history, print_history(&1))
   end
 

lib/iex/lib/iex/options.ex

@@ -64,6 +64,11 @@ defmodule IEx.Options do
     opts
   end
 
+  def get(:history_size) do
+    { :ok, size } = :application.get_env(:iex, :history_size)
+    size
+  end
+
   def get(name) do
     raise_option(name)
   end
@@ -97,7 +102,7 @@ defmodule IEx.Options do
   end
 
   def set(:colors, _) do
-    raise_value
+    raise_value("a keyword list")
   end
 
   def set(:inspect, opts) when is_list(opts) do
@@ -108,7 +113,17 @@ defmodule IEx.Options do
   end
 
   def set(:inspect, _) do
-    raise_value
+    raise_value("a keyword list")
+  end
+
+  def set(:history_size, size) when is_integer(size) do
+    old_size = get(:history_size)
+    :application.set_env(:iex, :history_size, size)
+    old_size
+  end
+
+  def set(:history_size, _) do
+    raise_value("an integer")
   end
 
   def set(name, _) do
@@ -191,8 +206,8 @@ defmodule IEx.Options do
     raise ArgumentError, message: "Unknown IEx option #{inspect name}"
   end
 
-  defp raise_value do
-    raise ArgumentError, message: "Expected the value to be a keyword list"
+  defp raise_value(type) do
+    raise ArgumentError, message: "Expected the value to be #{type}"
   end
 
   defp filtered_kw(reference_kw, user_kw) do

lib/iex/lib/iex/server.ex

@@ -4,13 +4,14 @@ defmodule IEx.Server do
   @doc """
   Eval loop for an IEx session. Its responsibilities include:
 
+    * loading of .iex files
     * reading input
     * trapping exceptions in the code being evaluated
-    * keeping input history
+    * keeping expression history
 
   """
   def start(config) do
-    Process.put :iex_history, []
+    Process.put :iex_history, :queue.new
 
     { _, _, scope } = :elixir.eval('require IEx.Helpers', [], 0, config.scope)
     config = config.scope(scope)
@@ -135,8 +136,29 @@ defmodule IEx.Server do
   end
 
   defp update_history(config) do
-    current = Process.get :iex_history
-    Process.put :iex_history, [config|current]
+    limit = IEx.Options.get(:history_size)
+    history = Process.get(:iex_history)
+    len = :queue.len(history)
+    new_history =
+      :queue.in(config, history)
+      |> limit_history(len + 1, limit)
+    Process.put(:iex_history, new_history)
+  end
+
+  defp limit_history(_, _, 0) do
+    :queue.new
+  end
+
+  defp limit_history(queue, _, limit) when limit < 0 do
+    queue
+  end
+
+  defp limit_history(queue, len, limit) when len > limit do
+    limit_history(:queue.drop(queue), len-1, limit)
+  end
+
+  defp limit_history(queue, _, _) do
+    queue
   end
 
   defp io_get(config) do

lib/iex/mix.exs

@@ -17,6 +17,7 @@ defmodule IEx.Mixfile do
         directory: "blue",
         device: "green"
       ],
+      history_size: 20,
       started: true
     ]]
   end