*swallow?* (clj)

Dynamic var. If bound to a logically true value in closing thread, will swallow any `java.lang.Throwable`, the apex class for all exceptions in Java and Clojure. You may change its value is some nested maps with meta `{::swallow false}`. Because `clojure.walk/walk` is used for map traversal, it is not possible to pass down any argument. Also, as we iteratively walk through nested data structures, some of them do not support metadata. As a result, a binding on this dynamic var in the execution thread enables a simple way to remember the parent value as we visit the children.