     transformer.rule(["a": .simple("a"), "b": .simple("b"), "op": .literal("-")]) {
         try Minus(first: $0.val("a"), second: $0.val("b"))
     }
-    
+
     transformer.rule(["a": .simple("a"), "b": .simple("b"), "op": .literal("*")]) {
         try Times(first: $0.val("a"), second: $0.val("b"))
     }
-    
+
+    transformer.rule(["a": .simple("a"), "b": .simple("b"), "op": .literal("/")]) {
+        try Divide(first: $0.val("a"), second: $0.val("b"))
+    }
+
     return transformer
 }


enum ExprError: Error {
    case notAConstant
    case unexpectedRemainder
}

func makeArithmeticTransformer() -> Transformer<Expr> {

    let first: Expr
    let second: Expr

    func evaluate() -> Double {
        return first.evaluate() + second.evaluate()
    }
}
