wall

wall

This operator delimits lexical scope. It creates a new environment sealed off from its parent, thus sandboxing code beneath it.

(def x 1)
(def y 2)
(def z 3)

(wall (a x b (+ y 1))
   (+ a b))             ; 4

(wall (a 1 b 2)
   z)                   ; (runtime-error (undefined-symbol z "Name not defined."))