$ perl -MO=Concise -e 'sub foo(){42}; print foo'
6  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 2 -e:1) v:{ ->3
5     <@> print vK ->6
3        <0> pushmark s ->4
4        <$> const[IV 42] s ->5
-e syntax OK

$ perl -MO=Concise -e 'sub foo(){42}; print &foo'
8  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 2 -e:1) v:{ ->3
7     <@> print vK ->8
3        <0> pushmark s ->4
6        <1> entersub[t2] lK/TARG,AMPER,1 ->7
-           <1> ex-list lK ->6
4              <0> pushmark s ->5
-              <1> ex-rv2cv sK/8 ->-
5                 <#> gv[*foo] s ->6
-e syntax OK