void ex12()
{
  TFile* f = TFile::Open("ex12.root") ;
  TH1* h_sig = f->Get("h_sig") ;
  TH1* h_bkg = f->Get("h_bkg") ;
  TH1* h_data = f->Get("h_data") ;
  
  // Create a workspace with observable x[0,120]
  RooWorkspace w("w",1) ;
  w.factory("x[0,120]") ;

  // Tie TF1 h_sig to observable x in RooFit binned dataset dh_sig
  RooDataHist dh_sig("dh_sig","dh_sig",w::x,h_sig) ;

  // Import both datasets in the workspace
  w.import(dh_sig) ;
  
  w.factory("HistFunc::hf_sig(x,dh_sig)") ;

  RooPlot* frame = w.var("x")->frame();
  w.function("hf_sig")->plotOn(frame) ;
  frame->Draw() ;
}