[Rd] Dynamic list creation (SEXP in C) returns error "unimplemented type (29) in 'duplicate'" Dynamic list creation (SEXP in C) returns error

[Radford Neal]

"changing its size using SETLENGTH (Rf_lengthgets)"

NO! NO! NO!  SETLENGTH does not do the same thing as Rf_lengthgets.
You should never use SETLENGTH, which is not part of the API, and
really should not even exist.

For that matter Rf_lengthgets is also not part of the API.  I
recommend getting the length right to start with.

   Radford Neal