Nice article, good summary of the purpose of unidirectional UI approach like Redux's, although it doesn't get as much into persistent data structures as maybe i

Nice article, good summary of the purpose of unidirectional UI approach like Redux's, although it doesn't get as much into persistent data structures as maybe it could have. What's the point of the exclamation mark after certain function names? Is that a pseudocode thing? Is that supposed to be shorthand for an impure function? (if so, not sure why `handleKeyboardEvent` doesn't have an exclamation mark.