$ perl -wle " 0+$foo;  LABEL: for(1,2){ eval { next LABEL; }; }"
Useless use of addition (+) in void context at -e line 1.
Name "main::foo" used only once: possible typo at -e line 1.
Use of uninitialized value $foo in addition (+) at -e line 1.
Exiting eval via next at -e line 1.
Exiting eval via next at -e line 1.

$ perl -wle " no warnings q[exiting]; 0+$foo;  LABEL: for(1,2){ eval { next LABEL; }; }"
Useless use of addition (+) in void context at -e line 1.
Name "main::foo" used only once: possible typo at -e line 1.
Use of uninitialized value $foo in addition (+) at -e line 1.