+ (and (every (lambda (arg)
+ (%constantp arg environment envp))
+ (cdr form))
+ ;; Even though the function may be marked as foldable
+ ;; the call may still signal an error -- eg: (CAR 1).
+ (handler-case
+ (progn
+ (constant-function-call-value form environment envp)
+ t)
+ (error () nil))))))