feat(calc): supports function definition and evaluation

3 files changed, 70 insertions, 3 deletions

diff --git a/lib/elixir_math_parser.ex b/lib/elixir_math_parser.ex
index 286829e..b7f080c 100644
--- a/lib/elixir_math_parser.ex
+++ b/lib/elixir_math_parser.ex
@@ -5,6 +5,7 @@ defmodule ElixirMathParser do
   alias ElixirMathParser.Math.Rational
   alias ElixirMathParser.Math.Calc
   alias ElixirMathParser.Math.Conversion
+  alias ElixirMathParser.Math.Function
 
   defp reduce_to_value({:int, _line, value}, _state) do
     {:ok, Rational.new(value)}
@@ -76,11 +77,35 @@ defmodule ElixirMathParser do
     end
   end
 
+  defp reduce_to_value({:eval_func, {:var, line, var}, params}, state) do
+    if !Map.has_key?(state, var) do
+      {:error, line, "function " <> to_string(var) <> " not found"}
+    else
+      v = state[var]
+
+      # check if the mult is implicit
+      if Rational.is_rational(v) do
+        [head | _] = params
+        reduce_to_value({:mul_op, {:var, line, var}, head}, state)
+      else
+        params = Enum.map(params, fn v -> with {:ok, v} <- reduce_to_value(v, state), do: v end)
+
+        with {:ok, v} <- state[var] |> Function.eval(params) do
+          {:ok, v}
+        else
+          {:error, reason} -> {:error, line, reason}
+          {:error, line, reason} -> {:error, line, reason}
+        end
+      end
+    end
+  end
+
   defp evaluate_tree([{:assign, {:var, line, lhs}, rhs} | tail], state) do
     with {:ok, val} <- reduce_to_value(rhs, state) do
       evaluate_tree(tail, Map.merge(state, %{lhs => val}))
     else
       {:error, reason} -> {:error, line, reason}
+      {:error, line, reason} -> {:error, line, reason}
     end
   end
 
@@ -92,6 +117,21 @@ defmodule ElixirMathParser do
     end
   end
 
+  defp evaluate_tree([{:assign_func, {:var, _line, name}, vars, expr} | tail], state) do
+    fun =
+      Function.new(
+        fn params, given ->
+          state =
+            Enum.reduce(given, state, fn {v, id}, acc -> Map.merge(acc, %{params[id] => v}) end)
+
+          reduce_to_value(expr, state)
+        end,
+        Enum.map(vars, fn {:var, _line, name} -> name end)
+      )
+
+    evaluate_tree(tail, Map.merge(state, %{name => fun}))
+  end
+
   defp evaluate_tree([], state) do
     {:ok, state}
   end
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.