[R-pkg-devel] Only printing a message once per top-level call.

[Pavel N. Krivitsky]

Dear All,

I have a package (ergm, in case you are wondering) that has some low-
level routines (say, low()) that produce messages that the end-user
needs to see and that tend to be called multiple times for every time
the top-level routine (say, high()) is called, often by other routines
that are top-level routines themselves.

What I'd like to do to have the low-level routine print the message the
first time it's called for a given top-level call, and then "remember"
and stay silent the next time to avoid spamming the end-user.

In other words,
   1. high()
      1. low()
         1. print message
      2. low()
         1. don't print message
      3. high()
         1. low()
            1. don't print message
   2. high()
      1. low()
         1. print message

One way to do that that I can see is to use local() to create a
blacklist of messages that have already been printed, which get cleared
every time the top-level call exists. I.e.,
   1. Use local() with a list of messages printed so far and a status of
      "active" or "inactive" (the initial state), which returns  a
      function that can query and update both of those.
   2. When high() is called, it first checks if the blacklist is active. 
      1. If it's active, then this high() must have been called from
         another high(), so it leaves the blacklist alone.
      2. If it's inactive, then it must be the top-level call, so it sets
         it to active and sets an on.exit() handler to clear the blacklist
         and set it to inactive.
   3. When low() wants to print a message, it queries the blacklist to see
      if it's already printed it. If not, it prints and adds it to the
      list.
   4. When the top-level high() finishes, the blacklist is cleared and set
      to inactive.

However, I wonder if there already is a way to do that, ideally built
in.

					Any thoughts?
					Pavel



-- 
Pavel Krivitsky
Lecturer in Statistics
National Institute of Applied Statistics Research Australia (NIASRA)
School of Mathematics and Applied Statistics | Building 39C Room 154
University of Wollongong NSW 2522 Australia
T +61 2 4221 3713
Web (NIASRA): http://niasra.uow.edu.au/index.html
Web (Personal): http://www.krivitsky.net/research
ORCID: 0000-0002-9101-3362

NOTICE: This email is intended for the addressee named and may contain
confidential information. If you are not the intended recipient, please
delete it and notify the sender. Please consider the environment before
printing this email.