diff --git a/lib/list_ops.ex b/lib/list_ops.ex
index 3010084..672cdba 100644
--- a/lib/list_ops.ex
+++ b/lib/list_ops.ex
@@ -1,2 +1,41 @@
 defmodule ListOps do
+  def count(list) do
+    reduce(list, 0, fn(_x,acc) -> acc + 1 end)
+  end
+
+  def reverse(list) do
+    reduce(list, [], fn(x, acc) -> [x | acc] end)
+  end
+
+  def map(list, mapper) do
+    list
+      |> reduce([], fn(x, acc) -> [mapper.(x) | acc] end)
+      |> reverse
+  end
+
+  def filter(list, filter_fun) do
+    reduce(list, [], fn(x, acc) ->
+      if filter_fun.(x), do: [x | acc], else: acc
+    end) |> reverse
+  end
+
+  def append(list, other) do
+    concat([list, other])
+  end
+
+  def concat(list_of_lists) do
+    reduce(list_of_lists, [], fn(x, acc) ->
+      reduce(x, acc, fn(y, acc2) ->
+        [y | acc2]
+      end)
+    end) |> reverse
+  end
+
+  def reduce(list, acc, step_fun)
+  def reduce([h | tail], acc, step_fun) do
+    reduce(tail, step_fun.(h,acc), step_fun)
+  end
+  def reduce([], acc, _step_fun) do
+    acc
+  end
 end
diff --git a/test/list_ops_test.exs b/test/list_ops_test.exs
index 99f06ff..db343fa 100644
--- a/test/list_ops_test.exs
+++ b/test/list_ops_test.exs
@@ -27,85 +27,85 @@ defmodule ListOpsTest do
     assert ListOps.reverse(Enum.to_list(1..1_000_000)) == Enum.to_list(1_000_000..1)
   end
 
-  # test "map of empty list" do
-  #   assert ListOps.map([], &(&1+1)) == []
-  # end
-  #
-  # test "map of normal list" do
-  #   assert ListOps.map([1,3,5,7], &(&1+1)) == [2,4,6,8]
-  # end
-  #
-  # test "map of huge list" do
-  #   assert ListOps.map(Enum.to_list(1..1_000_000), &(&1+1)) ==
-  #     Enum.to_list(2..1_000_001)
-  # end
-  #
-  # test "filter of empty list" do
-  #   assert ListOps.filter([], &odd?/1) == []
-  # end
-  #
-  # test "filter of normal list" do
-  #   assert ListOps.filter([1,2,3,4], &odd?/1) == [1,3]
-  # end
-  #
-  # test "filter of huge list" do
-  #   assert ListOps.filter(Enum.to_list(1..1_000_000), &odd?/1) ==
-  #     Enum.map(1..500_000, &(&1*2-1))
-  # end
-  #
-  # test "reduce of empty list" do
-  #   assert ListOps.reduce([], 0, &(&1+&2)) == 0
-  # end
-  #
-  # test "reduce of normal list" do
-  #   assert ListOps.reduce([1,2,3,4], -3, &(&1+&2)) == 7
-  # end
-  #
-  # test "reduce of huge list" do
-  #   assert ListOps.reduce(Enum.to_list(1..1_000_000), 0, &(&1+&2)) ==
-  #     Enum.reduce(1..1_000_000, 0, &(&1+&2))
-  # end
-  #
-  # test "reduce with non-commutative function" do
-  #   assert ListOps.reduce([1,2,3,4], 10, fn x, acc -> acc - x end) == 0
-  # end
-  #
-  # test "append of empty lists" do
-  #   assert ListOps.append([], []) == []
-  # end
-  #
-  # test "append of empty and non-empty list" do
-  #   assert ListOps.append([], [1,2,3,4]) == [1,2,3,4]
-  # end
-  #
-  # test "append of non-empty and empty list" do
-  #   assert ListOps.append([1,2,3,4], []) == [1,2,3,4]
-  # end
-  #
-  # test "append of non-empty lists" do
-  #   assert ListOps.append([1,2,3], [4,5]) == [1,2,3,4,5]
-  # end
-  #
-  # test "append of huge lists" do
-  #   assert ListOps.append(Enum.to_list(1..1_000_000), Enum.to_list(1_000_001..2_000_000)) ==
-  #     Enum.to_list(1..2_000_000)
-  # end
-  #
-  # test "concat of empty list of lists" do
-  #   assert ListOps.concat([]) == []
-  # end
-  #
-  # test "concat of normal list of lists" do
-  #   assert ListOps.concat([[1,2],[3],[],[4,5,6]]) == [1,2,3,4,5,6]
-  # end
-  #
-  # test "concat of huge list of small lists" do
-  #   assert ListOps.concat(Enum.map(1..1_000_000, &[&1])) ==
-  #     Enum.to_list(1..1_000_000)
-  # end
-  #
-  # test "concat of small list of huge lists" do
-  #   assert ListOps.concat(Enum.map(0..9, &Enum.to_list((&1*100_000+1)..((&1+1)*100_000)))) ==
-  #     Enum.to_list(1..1_000_000)
-  # end
+   test "map of empty list" do
+     assert ListOps.map([], &(&1+1)) == []
+   end
+
+   test "map of normal list" do
+     assert ListOps.map([1,3,5,7], &(&1+1)) == [2,4,6,8]
+   end
+
+   test "map of huge list" do
+     assert ListOps.map(Enum.to_list(1..1_000_000), &(&1+1)) ==
+       Enum.to_list(2..1_000_001)
+   end
+
+   test "filter of empty list" do
+     assert ListOps.filter([], &odd?/1) == []
+   end
+
+   test "filter of normal list" do
+     assert ListOps.filter([1,2,3,4], &odd?/1) == [1,3]
+   end
+
+   test "filter of huge list" do
+     assert ListOps.filter(Enum.to_list(1..1_000_000), &odd?/1) ==
+       Enum.map(1..500_000, &(&1*2-1))
+   end
+
+   test "reduce of empty list" do
+     assert ListOps.reduce([], 0, &(&1+&2)) == 0
+   end
+
+   test "reduce of normal list" do
+     assert ListOps.reduce([1,2,3,4], -3, &(&1+&2)) == 7
+   end
+
+   test "reduce of huge list" do
+     assert ListOps.reduce(Enum.to_list(1..1_000_000), 0, &(&1+&2)) ==
+       Enum.reduce(1..1_000_000, 0, &(&1+&2))
+   end
+
+   test "reduce with non-commutative function" do
+     assert ListOps.reduce([1,2,3,4], 10, fn x, acc -> acc - x end) == 0
+   end
+
+   test "append of empty lists" do
+     assert ListOps.append([], []) == []
+   end
+
+   test "append of empty and non-empty list" do
+     assert ListOps.append([], [1,2,3,4]) == [1,2,3,4]
+   end
+
+   test "append of non-empty and empty list" do
+     assert ListOps.append([1,2,3,4], []) == [1,2,3,4]
+   end
+
+   test "append of non-empty lists" do
+     assert ListOps.append([1,2,3], [4,5]) == [1,2,3,4,5]
+   end
+
+   test "append of huge lists" do
+     assert ListOps.append(Enum.to_list(1..1_000_000), Enum.to_list(1_000_001..2_000_000)) ==
+       Enum.to_list(1..2_000_000)
+   end
+
+   test "concat of empty list of lists" do
+     assert ListOps.concat([]) == []
+   end
+
+   test "concat of normal list of lists" do
+     assert ListOps.concat([[1,2],[3],[],[4,5,6]]) == [1,2,3,4,5,6]
+   end
+
+   test "concat of huge list of small lists" do
+     assert ListOps.concat(Enum.map(1..1_000_000, &[&1])) ==
+       Enum.to_list(1..1_000_000)
+   end
+
+   test "concat of small list of huge lists" do
+     assert ListOps.concat(Enum.map(0..9, &Enum.to_list((&1*100_000+1)..((&1+1)*100_000)))) ==
+       Enum.to_list(1..1_000_000)
+   end
 end