example: simply output a message on the console

let logTrace = traceWith $ showTracing $ stdoutTracer
in  logTrace "hello world"

example: calling a function and passing in a Tracer

example1 :: IO ()
example1 = do
    let logTrace a = traceWith (showTracing (contramap ("Debug: " ++) stdoutTracer)) a
    void $ callFun1 logTrace

callFun1 :: (String -> IO ()) -> IO Int
callFun1 logTrace = do
    logTrace "in function 1"
    return 42

runTracer evaluates a Tracer (i.e. consumes its argument)