0584 Macros Example

Author: knowthen

lectures/macros/macro_proposition.exs

@@ -0,0 +1,23 @@
+defmodule Proposition do
+  defstruct [:description, yes: 0, no: 0]
+
+  def new(description) do
+    %Proposition{description: description}
+  end
+  
+  defmacro vote({:+, _, [prop, qty]}) do
+    cast(prop, :yes, qty)
+  end
+  
+  defmacro vote({:-, _, [prop, qty]}) do
+    cast(prop, :no, qty)
+  end
+  
+  defp cast(prop, vote, qty) do
+    quote do
+      Map.update!(unquote(prop), unquote(vote), &(&1 + unquote(qty)))
+    end  
+  end
+  
+end
+