The advantage of .Primitive over .Internal
functions is the potential efficiency of argument passing, and that
positional matching can be used where desirable, e.g.\ifelse{latex}{\out{~}}{ } in
switch. For more details, see the R Internals
Manual. All primitive functions are in the base namespace.
This function is almost never used: `name` or, more carefully,
get(name, envir = baseenv()) work equally well and do
not depend on knowing which functions are primitive (which does change
as R evolves).