Real robust_scm2double (SCM, double);
int robust_scm2int (SCM, int);
+Direction robust_scm2dir (SCM, Direction);
Drul_array<Real> robust_scm2drul (SCM, Drul_array<Real>);
Interval robust_scm2interval (SCM, Drul_array<Real>);
Offset robust_scm2offset (SCM, Offset);