$ perl -MO=Concise,-exec -MDevel::Peek -we'Dump 1; sub foo{Dump $_[0];$_[0]=1} foo(1)'
1  <0> enter
2  <;> nextstate(main 44 -e:1) v:{
3  <$> const[IV 1] s
4  <2> Devel_Peek_Dump vK/1
5  <;> nextstate(main 46 -e:1) v:{
6  <0> pushmark s
7  <$> const[IV 1] sM
8  <#> gv[IV \&main::foo] s
9  <1> entersub vKS
a  <@> leave[1 ref] vKP/REFC
-e syntax OK