case '/':    /* may be division, defined-or, or pattern */
         if ((PL_expect == XOPERATOR || PL_expect == XTERMORDORDOR) && s[1] == '/') {
            ...
            AOPERATOR(DORDOR);
        }
        else if (PL_expect == XOPERATOR) {
            ...
            Mop(OP_DIVIDE);
        }
        else {
            ...
            s = scan_pat(s,OP_MATCH);
        }

##</code><code>##

    case '.':
        ...
        if (PL_expect == XOPERATOR || !isDIGIT(s[1])) {
            ...
            Aop(OP_CONCAT)

##</code><code>##

$ 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);

##</code><code>##

$ perl -E 'say 1 .5'
15