Add Stream.iterate

Author: pragdave

lib/elixir/lib/stream.ex

@@ -89,15 +89,10 @@ defmodule Stream do
   to `Stream.map/2`, we have automatically created a stream that will
   multiply the items in the list by 2 on enumeration.
 
-  This module also provides other functions for creating streams, like
+  This module also provides other functions for creating streams, such as
   `Stream.cycle/1`.
   """
 
-  @compile {:inline, increment_func: 0}
-
-  @doc false
-  def increment_func(), do: &1+1
-
   defrecord Lazy, [:enumerable, :fun, :acc]
 
   defimpl Enumerable, for: Lazy do
@@ -225,6 +220,27 @@ defmodule Stream do
          end]
   end
 
+  @doc """
+  Emit a sequence of values, starting with `start_value`. Successive
+  values are generated by calling `next_fun` on the previous value.
+
+
+  ## Examples
+
+      iex> Stream.iterate(0, &1+1)  |> Enum.take(5)
+      [0,1,2,3,4]
+
+  """
+
+  @spec iterate(element, (element -> element)) :: Lazy.t
+  def iterate(start_value, next_fun) do
+     do_iterate(start_value, next_fun, &1, &2)
+  end
+
+  defp do_iterate(start_value, next_fun, acc, fun) do
+    do_iterate(next_fun.(start_value), next_fun, fun.(start_value, acc), fun)
+  end
+
   @doc """
   Creates a stream that will apply the given function on
   enumeration.
@@ -267,27 +283,6 @@ defmodule Stream do
          end]
   end
 
-  @doc """
-  Emit a sequence of values, starting with `start_value`. Successive
-  values are generated by calling `incr_func` on the previous value.
-  The default parameters generate a sequence of integers starting at 0.
-
-  ## Examples
-
-      iex> Stream.seq  |> Enum.take(5)
-      [0,1,2,3,4]
-
-  """
-
-  @spec seq((element -> element), element) :: Lazy.t
-  def seq(incr_fun // &1+1, start_value // 0) do
-     do_seq(incr_fun, start_value, &1, &2)
-  end
-
-  defp do_seq(incr_fun, start_value, acc, fun) do
-    do_seq(incr_fun, incr_fun.(start_value), fun.(start_value, acc), fun)
-  end
-
 
   @doc """
   Lazily takes the next `n` items from the enumerable and stops

lib/elixir/test/elixir/stream_test.exs

@@ -55,6 +55,13 @@ defmodule StreamTest do
     assert Enum.to_list(stream) == [2]
   end
 
+  test :iterate do
+    stream = Stream.iterate(0, &1+2)
+    assert Enum.take(stream, 5) == [0,2,4,6,8]
+    stream = Stream.iterate(5, &1+2)
+    assert Enum.take(stream, 5) == [5,7,9,11,13]
+  end
+
   test :map do
     stream = Stream.map([1,2,3], &1 * 2)
     assert is_lazy(stream)
@@ -67,23 +74,6 @@ defmodule StreamTest do
     assert Enum.to_list(stream) == [1,3]
   end
 
-  test :seq_default do
-    stream = Stream.seq
-    assert Enum.take(stream, 5) == [0,1,2,3,4]
-  end
-
-  test :seq_with_explicit_but_default do
-    stream = Stream.seq(&1+1, 0)
-    assert Enum.take(stream, 5) == [0,1,2,3,4]
-  end
-
-  test :seq_for_every_second_number do
-    stream = Stream.seq(&1+2)
-    assert Enum.take(stream, 5) == [0,2,4,6,8]
-    stream = Stream.seq(&1+2, 5)
-    assert Enum.take(stream, 5) == [5,7,9,11,13]
-  end
-
   test :take do
     stream = Stream.take(1..1000, 5)
     assert is_lazy(stream)