2 files changed, 30 insertions, 3 deletions
diff --git a/lib/math/function.ex b/lib/math/function.ex
new file mode 100644
index 0000000..2acf2c4
--- /dev/null
+++ b/lib/math/function.ex
@@ -0,0 +1,28 @@
+defmodule ElixirMathParser.Math.Function do
+  alias ElixirMathParser.Math.Function
+
+  defstruct relation: nil, parameters: %{}
+
+  def is_function(val) when is_map(val) and is_map_key(val, :__struct__) and is_struct(val),
+    do: :erlang.map_get(:__struct__, val) == __MODULE__
+
+  def new(relation, parameters) do
+    params =
+      Enum.with_index(parameters)
+      |> Enum.reduce(%{}, fn {v, id}, acc -> Map.merge(acc, %{id => v}) end)
+
+    %Function{relation: relation, parameters: params}
+  end
+
+  def eval(fun, parameters) do
+    if Enum.count(parameters) != Enum.count(fun.parameters) do
+      {:error, "wrong count of parameters"}
+    else
+      params =
+        Enum.with_index(parameters)
+        |> Enum.reduce(%{}, fn {v, id}, acc -> Map.merge(acc, %{v => id}) end)
+
+      fun.relation.(fun.parameters, params)
+    end
+  end
+end
diff --git a/lib/math/rational.ex b/lib/math/rational.ex
index c3d94c9..e788883 100644
--- a/lib/math/rational.ex
+++ b/lib/math/rational.ex
@@ -83,9 +83,8 @@ defmodule ElixirMathParser.Math.Rational do
   iex> Rational.is_rational("My quick brown fox")
   false
   """
-  defguard is_rational(val)
-           when is_map(val) and is_map_key(val, :__struct__) and is_struct(val) and
-                  :erlang.map_get(:__struct__, val) == __MODULE__
+  def is_rational(val) when is_map(val) and is_map_key(val, :__struct__) and is_struct(val),
+    do: :erlang.map_get(:__struct__, val) == __MODULE__
 
   @doc """
   Creates a new Rational number.