Add reduce to Enum.Iterator protocol

Author: ericmj

lib/elixir/lib/enum.ex

@@ -16,6 +16,8 @@ defprotocol Enum.Iterator do
 
   @only [List, Record, Function]
 
+  def reduce(collection, acc, fun)
+
   @doc """
   This function must return a tuple of the form `{ iter, step }` where
   `iter` is a function that yields successive values from the collection
@@ -1935,6 +1937,14 @@ defmodule Enum do
 end
 
 defimpl Enum.Iterator, for: List do
+  def reduce([h|t], acc, fun) do
+    reduce(t, fun.(h, acc), fun)
+  end
+
+  def reduce([], acc, _fun) do
+    acc
+  end
+
   def iterator(list), do: list
 
   def member?([], _),       do: false
@@ -1944,6 +1954,10 @@ defimpl Enum.Iterator, for: List do
 end
 
 defimpl Enum.Iterator, for: Function do
+  def reduce(function, acc, fun) do
+    function.(acc, fun)
+  end
+
   def iterator(function) do
     { iterator, first } = function.()
     { iterator, iterator.(first) }

lib/elixir/lib/hash_dict.ex

@@ -333,6 +333,14 @@ defmodule HashDict do
     drop(delete(dict, key), keys)
   end
 
+  def reduce(ordered(bucket: bucket), acc, fun) do
+    :lists.foldl(fun, acc, bucket)
+  end
+
+  def reduce(trie() = dict, acc, fun) do
+    dict_fold(dict, acc, fun)
+  end
+
   ## Dict-wide functions
 
   defp dict_get(ordered(bucket: bucket), key) do
@@ -579,6 +587,7 @@ defmodule HashDict do
 end
 
 defimpl Enum.Iterator, for: HashDict do
+  def reduce(dict, acc, fun),  do: HashDict.reduce(dict, acc, fun)
   def iterator(dict),          do: HashDict.to_list(dict)
   def member?(dict, { k, v }), do: match?({ :ok, ^v }, HashDict.fetch(dict, k))
   def member?(_dict, _),       do: false

lib/elixir/lib/range.ex

@@ -5,6 +5,8 @@ defrecord Range, [:first, :last] do
 end
 
 defprotocol Range.Iterator do
+  def reduce(first, range, acc, fun)
+
   @doc """
   How to iterate the range, receives the first
   and range as arguments. It needs to return a
@@ -21,6 +23,10 @@ defprotocol Range.Iterator do
 end
 
 defimpl Enum.Iterator, for: Range do
+  def reduce(Range[first: first] = range, acc, fun) do
+    Range.Iterator.reduce(first, range, acc, fun)
+  end
+
   def iterator(Range[first: first] = range) do
     iterator = Range.Iterator.iterator(first, range)
     { iterator, iterator.(first) }
@@ -36,6 +42,31 @@ defimpl Enum.Iterator, for: Range do
 end
 
 defimpl Range.Iterator, for: Number do
+  def reduce(first, Range[last: last], acc, fun) when is_integer(first) and is_integer(last) do
+    reducer = if last >= first do
+      fn(acc, fun) -> do_reducer_up(first, last, acc, fun) end
+    else
+      fn(acc, fun) -> do_reducer_down(first, last, acc, fun) end
+    end
+    Enum.Iterator.Function.reduce(reducer, acc, fun)
+  end
+
+  defp do_reducer_up(counter, last, acc, fun) do
+    if counter > last do
+      acc
+    else
+      do_reducer_up(counter + 1, last, fun.(counter, acc), fun)
+    end
+  end
+
+  defp do_reducer_down(counter, last, acc, fun) do
+    if counter < last do
+      acc
+    else
+      do_reducer_down(counter - 1, last, fun.(counter, acc), fun)
+    end
+  end
+
   def iterator(first, Range[last: last]) when is_integer(first) and is_integer(last) and last >= first do
     fn(current) ->
       if current > last, do: :stop, else: { current, current + 1 }