Create conditional statement

mach/lib/mach/statement/if.ex

@@ -0,0 +1,60 @@
+defmodule Mach.Statement.If do
+  alias Mach.Statement.DoNothing
+  alias Mach.Boolean
+
+  defstruct [
+    condition: %Boolean{value: true},
+    consequence: %DoNothing{},
+    alternative: %DoNothing{},
+    _reducible?: true
+  ]
+
+  @doc """
+  Reduce conditional statements
+
+    iex(1)> Mach.Statement.If.reduce(
+    iex(1)>   %{},
+    iex(1)>   %Mach.Statement.If{
+    iex(1)>     condition: %Mach.LessThan{
+    iex(1)>       left: %Mach.Number{value: 4},
+    iex(1)>       right: %Mach.Number{value: 5},
+    iex(1)>     }
+    iex(1)>   }
+    iex(1)> )
+    {%{}, %Mach.Statement.If{condition: %Mach.Boolean{value: true}}}
+  """
+  def reduce(env, %{condition: %{_reducible?: true}} = statement) do
+    condition = statement.condition
+    reduced_condition = condition.__struct__.reduce(env, condition)
+    {env, %Mach.Statement.If{statement | condition: reduced_condition}}
+  end
+
+  def reduce(env, %{condition: %Boolean{value: true},
+                    consequence: %{_reducible?: true}} = statement) do
+    consequence = statement.consequence
+    reduced_consequence = consequence.__struct__.reduce(env, consequence)
+    {env, %Mach.Statement.If{statement | consequence: reduced_consequence}}
+  end
+
+  def reduce(env, %{condition: %Boolean{value: true}} = statement ) do
+    {env, statement.consequence}
+  end
+
+  def reduce(env, %{condition: %Boolean{value: false},
+                    alternative: %{_reducible?: true}} = statement) do
+    alternative = statement.alternative
+    reduced_alternative = alternative.__struct__.reduce(env, alternative)
+    {env, %Mach.Statement.If{statement | alternative: reduced_alternative}}
+  end
+
+  def reduce(env, %{condition: %Boolean{value: false}} = statement) do
+    {env, statement.alternative}
+  end
+
+end
+
+defimpl String.Chars, for: Mach.Statement.If do
+  def to_string statement do
+    "if (#{statement.condition}) { #{statement.consequence} }"
+  end
+end

mach/test/mach/statement/if_test.exs

@@ -0,0 +1,19 @@
+defmodule Mach.Statement.IfTest do
+  use ExUnit.Case
+  alias Mach.Statement.If
+  alias Mach.Statement.DoNothing
+  alias Mach.GreaterThan
+  doctest If
+
+  test "#to_string" do
+    statement = %If{
+      condition: %GreaterThan{
+        left: %Mach.Number{value: 2},
+        right: %Mach.Number{value: 3},
+      }
+    }
+
+    assert String.Chars.to_string(statement) == "if (2 > 3) { do-nothing }"
+  end
+
+end