Pre-callback
Evaluating getCallbackText()
Post-callback
callbackTest => cb("Alice")
Evaluating getCallbackText()
callbackTest => cb("Bob")
Evaluating getCallbackText()
Callback returned: Alice Bob
https://github.com/aldonline/reactivity #define while(x) if(x)
Too bad April 1 is already gone, I'm kind of tempted to try and sneak that in.
Also, OP required Redshift. DO does not offer that.