If you buffer all I/O until the program has finished executing, I don't think this type of timer works. (The message to the user is displayed only after the pro

If you buffer all I/O until the program has finished executing, I don't think this type of timer works. (The message to the user is displayed only after the process you are trying to time completes, and then when the user clicks the button you are executing again) The program is equivalent to a pure function from (state, events) to (state, actions) and the computing device that evaluates this function can't leak any information to the function without evaluating it incorrectly. It can still leak information in how long it takes to evaluate the function, but there is no direct way to get this information back into the function. You could ask the user what time it is, or how long something took, but that starts to look suspicious fast!