diff --git a/README.md b/README.md
index 0e926ca..ad52537 100644
--- a/README.md
+++ b/README.md
@@ -60,6 +60,9 @@ Available Operators:
 - lt: `<`: less than
 - load: `load`: load a key from the provided input `(load ".container.app_id")`
 - has-key: `has-key`: check if a key is in the input: `(has-key ".container.app_id")`
+- let: `let`: assign a local variable: `(let x 10)`
+- setq: `setq`: assign a global variable: `(setq x 11)`
+- defun: `defun`: user-defined functions: `((defun greet (a) (write (+ "Hello " a "!"))) (greet "Alice"))`
 
 For example: `(> (load ".container.geometry.width") 300)` would match the first window where the width is greater than 300.
 
diff --git a/i3toolwait b/i3toolwait
index 0fe258b..c91c152 100755
--- a/i3toolwait
+++ b/i3toolwait
@@ -80,7 +80,7 @@ class Environment:
             '<': lambda _, _l, a, b: a < b,
             '>=': lambda _, _l, a, b: a >= b,
             '<=': lambda _, _l, a, b: a <= b,
-            '+': lambda _, _l, *a: sum(a),
+            '+': lambda _, _l, *a: functools.reduce(lambda a, b: a + b, a),
             '-': lambda _, _l, a, b: a - b,
             '*': lambda _, _l, *a: functools.reduce(lambda a, b: a * b, a),
             '/': lambda _, _l, a, b: a // b,