Function: LOOKUP

Source

(defun lookup (environment type name &key (error-p nil) (default-value nil))
  (loop
     for (.type .name . data) in environment
     when (and (eql .type type) (eql .name name))
       return (values data t)
     finally
       (if error-p
           (error "Sorry, No value for ~S of type ~S in environment ~S found."
                  name type environment)
           (values default-value nil))))