-  r_call(+Fun, +Options)
 - Construct and possibly call an R function. Fun can be an atom or
a compound, eg plot, or 
plot(width=3). The predicate also
supports multiple output destinations. Options processed:
- call(Bool)
 - If 
false (default true), do not call the result. 
- fcall(-Term)
 - Term is unified with the constructed call
 
- rvar(Var)
 - Variable for the output
 
- Compatibility
 - - This is a partial implementation of the corresponding
real predicate.