$ perl -MO=Deparse -e 'sub foo(&) {}; foo { "foo" } . 5'
sub foo (&) {
    
}
foo(sub {
    'foo';
}
) . 5;
-e syntax OK

$ perl -MO=Deparse -e 'sub foo(&) {}; foo { "foo" } .5'
Too many arguments for main::foo at -e line 1, at EOF
-e had compilation errors.
sub foo (&) {
    
}
&foo(sub {
    'foo';
}
, 0.5);