Add Mayo.List module and add atom, list validation methods to Mayo.Any

lib/mayo/any.ex

@@ -102,6 +102,40 @@ defmodule Mayo.Any do
     }}
   end
 
+  @doc """
+  Checks if the value is an atom.
+
+      iex> Mayo.Any.atom(:test)
+      :test
+
+      iex> Mayo.Any.atom("test")
+      {:error, %Mayo.Error{type: "any.atom"}}
+  """
+  def atom(value) when is_atom(value) or is_nil(value), do: value
+
+  def atom(_) do
+    {:error, %Mayo.Error{
+      type: "any.atom"
+    }}
+  end
+
+  @doc """
+  Checks if the value is a list.
+
+      iex> Mayo.Any.list([1, 2, 3])
+      [1, 2, 3]
+
+      iex> Mayo.Any.list("test")
+      {:error, %Mayo.Error{type: "any.list"}}
+  """
+  def list(value) when is_list(value) or is_nil(value), do: value
+
+  def list(_) do
+    {:error, %Mayo.Error{
+      type: "any.list"
+    }}
+  end
+
   @doc """
   Forbids any value except `nil`.
 

lib/mayo/list.ex

@@ -0,0 +1,58 @@
+defmodule Mayo.List do
+  @doc """
+  Checks the minimum number of elements in the list.
+
+      iex> Mayo.List.min([1, 2, 3], 3)
+      [1, 2, 3]
+
+      iex> Mayo.List.min([], 3)
+      {:error, %Mayo.Error{type: "list.min"}}
+  """
+  def min(value, len) when is_list(value) and length(value) == len, do: value
+
+  def min(value, _) when is_list(value) do
+    {:error, %Mayo.Error{
+      type: "list.min"
+    }}
+  end
+
+  def min(value, _), do: value
+
+  @doc """
+  Checks the maximum number of elements in the list.
+
+      iex> Mayo.List.max([1, 2, 3], 3)
+      [1, 2, 3]
+
+      iex> Mayo.List.max([1, 2, 3, 4], 3)
+      {:error, %Mayo.Error{type: "list.max"}}
+  """
+  def max(value, len) when is_list(value) and length(value) == len, do: value
+
+  def max(value, _) when is_list(value) do
+    {:error, %Mayo.Error{
+      type: "list.max"
+    }}
+  end
+
+  def max(value, _), do: value
+
+  @doc """
+  Checks the number of elements in the list.
+
+      iex> Mayo.List.length([1, 2, 3], 3)
+      [1, 2, 3]
+
+      iex> Mayo.List.length([1], 3)
+      {:error, %Mayo.Error{type: "list.length"}}
+  """
+  def length(value, len) when is_list(value) and length(value) == len, do: value
+
+  def length(value, _) when is_list(value) do
+    {:error, %Mayo.Error{
+      type: "list.length"
+    }}
+  end
+
+  def length(value, _), do: value
+end

test/mayo/list_test.exs

@@ -0,0 +1,4 @@
+defmodule Mayo.ListTest do
+  use ExUnit.Case
+  doctest Mayo.List
+end