I left it off mksref, because I wasn't sure how it should behave. It's an odd one.

I personally believe it should either complain if anything but exactly one argument is passed to it, or try to do something smart in that case, as I tried to, in my example. Another possibility would have been for it to return \[@_] but that would leave with two levels of indirection which is not consistent with the one argument case; further, it would amount to mksref mkaref LIST, so it doesn't make much sense.

Another possibility that springs to mind is the following: if there were an anonymous (circumfix) scalar ref constructor, it would impose scalar context to its arguments. Thus it should behave as follows:

sub mksref { my $x = +(@_)[-1]; \$x }
[download]

This looks like a job for prototypes. No, really :).

I can't see how prototypes could help there:

sub mkcref (@) {
   my @closed = @_;
   return sub { @closed};
}

sub mkaref (@) {
   return [@_];
}
[download]

The @ prototype does not do anything useful, since it just says that the arguments are an arbitrary list, which is the default anyway.

sub mkhref (%) {
    if ( @_%2 ) {
        warn "Odd number of elements in mkhref";
        return { @_, undef };
    }
    else {
        return {@_};
    }
}
[download]

There's not a % prototype that I know of. There's a \% one which does something entirely different. If there were I believe it should simply do the evenness check you're doing yourself.

Said this, my own version of mkhref() did something different: took a list and returned a hashref with the elements of that list as keys, and undef values. Given that these subs are supposed to be prefix alternatives to the circumfix [ ], { } and sub { } constructors, and to the non existant scalar ref one, my sub is certainly stupid and yours does the Right Thing™. But in the same vein, I would leave to perl to do its job of checking (if warnings are enabled) evennes:

sub mkhref { {@_} }
[download]

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