~$ perl -MO=Concise -e '$o->foo'
      entersub
         pushmark
         ex-rv2sv
            gvsv[*o] s
         method_named[PVIV "foo"]
~$ perl -MO=Concise -e 'foo( $o )'
      entersub
         ex-list
            pushmark
            ex-rv2sv
               gvsv[*o]
            ex-rv2cv
               gv[*foo]