.Primitive looks up by name a ‘primitive’
(internally implemented) function.
name of the R function.
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.in
switch. For more details, see the ‘R Internals
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).