$ perl -MO=Deparse -e "  sub foo (&) {}; foo {;;}   // 7 "
Number found where operator expected at -e line 1, near "// 7"
        (Missing operator before  7?)
Too many arguments for main::foo at -e line 1, near "// 7"
syntax error at -e line 1, near "// 7"
-e had compilation errors.
sub foo (&) {

}

$ perl -e " // 1 "
Number found where operator expected at -e line 1, near "// 1"
        (Missing operator before  1?)
syntax error at -e line 1, near "// 1"
Execution of -e aborted due to compilation errors.



$ perl -le "  sub foo (&) {}; foo sub{;;}   +// 7 "
Number found where operator expected at -e line 1, near "// 7"
        (Missing operator before  7?)
Type of arg 1 to main::foo must be block or sub {} (not addition (+)) at -e line 1, near "// 7"
syntax error at -e line 1, near "// 7"
Execution of -e aborted due to compilation errors.

$ perl -le "  sub foo (&) {}; foo sub{;;}   +//, 7 "
Type of arg 1 to main::foo must be block or sub {} (not addition (+)) at -e line 1, at EOF
Too many arguments for main::foo at -e line 1, at EOF
Execution of -e aborted due to compilation errors.

$ perl -le "  sub foo (&) {}; foo sub{;;}   ,//, 7 "
Too many arguments for main::foo at -e line 1, at EOF
Execution of -e aborted due to compilation errors.