+(defun filter-by-family (func form family)
+ "Handle a family-switch form.
+
+ Here, FUNC is a function of two arguments ITEM and FAMILY. FORM is either
+ a list of the form ((FAMILY . ITEM) ...), or an ITEM which is directly
+ acceptable to FUNC. Return a list of the resulting outputs of FUNC."
+
+ (if (and (listp form)
+ (every (lambda (clause)
+ (and (listp clause)
+ (family-addrclass (car clause))))
+ form))
+ (mapcan (lambda (clause)
+ (let ((fam (car clause)))
+ (and (or (eq family t)
+ (eq family fam))
+ (list (funcall func (cdr clause) fam)))))
+ form)
+ (list (funcall func form family))))
+