Loading required package: shiny
Loading required package: methods

Listening on http://127.0.0.1:8765
Warning: Error in badfunc: boom
Stack trace (innermost first):
    37: badfunc [${PWD}/stacktrace4/app.R#4]
    36: ui [${PWD}/stacktrace4/app.R#9]
     1: shiny::runApp [${SHINY}/R/server.R#685]
Error in badfunc() : boom
NULL