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Hello, For the BUILTINSXP and SPECIALSXP types, the R Internals page documents "An integer giving the offset into the table of primitives/.Internals. " What macro gives me the value of this integer? I guess something like this would work had R_USEINTERNALS been defined v->u.primsxp.offset (where v is a SEXP of either of the above types). What is the portable version? Thank you