typeof, so
operate at a level beneath S3/S4 etc.is_list(x)is_atomic(x)
is_vector(x)
is_numeric(x)
is_integer(x)
is_double(x)
is_character(x)
is_logical(x)
is.atomic(),is_atomic()does not
returnTRUEforNULL.is.vector(),is_vector()test if an
object is an atomic vector or a list.is.vectorchecks for the presence of attributes (other than name).is_numeric()is not generic so, (e.g.) dates and date times
areTRUE, notFALSE.