Creating symbolic references to a subroutine is fine, just not accessing them symbolically e.g

use strict;

sub foo {
  print "in foo(@_)";
}

my $f = \&{"foo"};
$f->("var");

## or more succinctly

(\&{"foo"})->("temp");

__output__

in foo(var)
in foo(temp)
[download]

And the bizarre error is due to eval trying to execute the return of M::y(), which is the return value of print.