Alters the user-supplied string x using make.names() with unique = TRUE
until it is a syntactically valid name not bound to in env nor its
parents.
h_generate_new_name(x, env)A string that does not match any of the bindings of env nor its
parents.
(string)
a candidate name.
(environment)
an environment whose bindings (and whose
parents' bindings) are checked to ensure that they do not include the
returned value.