Random mutations

src/formula.rs

@@ -22,11 +22,13 @@ impl Formula {
         }
         outputs
     }
-    pub fn mutate(&mut self) {}
 
     pub fn modify_tree(&mut self) -> NodeModifier {
         self.tree.modify_tree()
     }
+    pub fn modify_random_node(&mut self) -> NodeModifier {
+        self.tree.modify_node()
+    }
     pub fn display_tree(&self) {
         self.display_recursion(0, vec![&self.tree]);
     }