First commit creates an internal function containing checks common to all the cfr_() function
Second commit uses a collection so that the input data is completely validated in one go, and an error message with all the issues is returned. This prevents the user from having to try and error multiple times, with a different error message each time.
Thanks. Will review and merge into the latest 0.1.2 release PR #168 is complete (as seems like this is probably best sequence given CRAN submission was in limbo while this PR was added).
cfr_()
function