Problem Statement

Most operating systems provide interrupt facilities, sometimes called signals either generated by the user or as a result of program failure or reaching a limit like file space. Unhandled signals generally terminate a program in a disorderly manner. Signal handlers are created so that the program behaves in a well-defined manner upon receipt of a signal. Provide a program that displays an integer on each line of output at the rate of about one per half second. Upon receipt of the SIGINT signal (often generated by the user typing ctrl-C ( or better yet, SIGQUIT ctrl-\ )) the program will cease outputting integers, output the number of seconds the program has run, and then the program will quit.

Let's start with the solution:

global startTime

procedure main()
    startTime := &now
    trap("SIGINT", handler)
    every write(seq()) do delay(500)
end

procedure handler(s)
    stop("\n",&now-startTime," seconds")
end