Refactor function signatures to use slices

src/ast/compiler/optimizer/folder.rs

@@ -94,7 +94,7 @@ impl<'a> Folder<'a> {
             _ => return None,
         };
         let result = match func_val {
-            Value::Function(f) => (f.func)(arg_values),
+            Value::Function(f) => (f.func)(&arg_values),
             _ => return None,
         };
         Some(self.make_constant_node(result, callee))