+;;; GENSYM variant for easier debugging and better backtraces: append
+;;; the closest enclosing non-nil block name to the provided stem.
+(defun block-gensym (&optional (name "G") (env (when (boundp 'sb!c::*lexenv*)
+ (symbol-value 'sb!c::*lexenv*))))
+ (let ((block-name (when env
+ (car (find-if #'car (sb!c::lexenv-blocks env))))))
+ (if block-name
+ (gensym (format nil "~A[~S]" name block-name))
+ (gensym name))))
+