scottmascio2115 · January 8, 2017 15:37 · Jan 8, 2017
diff --git a/opposite.ex b/opposite.ex
@@ -0,0 +1,34 @@
+Creation of an opposite macro
+
+We want opposite 1 + 1
+to return to 0 or essentially run 1 - 1
+
+opposite 1 + 1
+Transforms 1 + 1 into an AST
+opposite({:+, [], [1,1]}
+
+Our macro would then transform that AST (Abstract syntax tree)
+
+The macro accepts an AST as an agruement
+
+defmacro opposite({:+, context, [a, b]}) do
+     {:- , context, [a, b]}
+end
+
+We can use the quote operator to generate the final AST:
+
+defmodule Math.Opposite do
+     defmacro opposite({:+, _, [a, b]}) do
+          quote do
+               unquote(a) - unquote(b)
+          end
+     end
+end
+
+Think of unquote as string interpolation for macros
+
+Usage
+
+import Math.Opposite
+
+opposite 1 + 1