(in-package :araneida) (defmacro seqlet (binding-forms &body body)   "Perform each of BINDING-FORMS sequentially in a lexical environment in which all the variables in BINDING-FORMS are visible.  Stop if any binding evaluates to NIL, setting all subsequent variables to NIL. Evaluate the body in this environment"   (let ((vars (mapcar #'car binding-forms)))     (labels ((foo (forms)                   (if forms                       `((setf ,(caar forms) ,(cadar forms))                         (when ,(caar forms) ,@(foo (cdr forms))))                     '())))       `(let ,vars          ,@(foo binding-forms)          ,@body))))