From ian@dial.pipex.com

% perl -e 'sub eququ(\$$) { ${$_[0]} = $_[1] unless defined ${$_[0]} } eququ $hash{$a}, 1;'
Type of arg 1 to main​::eququ must be scalar (not hash elem) at -e line
1, near "1;"

Err, why?

Especially as
  C<for($hash{$a}) { eququ $_,1 } >
works as required, i.e. sets the 'hash elem' as expected.

BTW, perlbug has its 'perl' executable hardwired to be the perl that
Configure thinks is installed (/usr/local/bin/perl) rather than
the perl I'm actually using (i.e. first "perl" on my PATH), which is is
different. This may be a feature, but it means that the info below the
line is useless.

This perlbug was built using Perl 5.00404 - Sun Apr 26 12:56:41 BST 1998
It is being executed now by  Perl 5.00557 - Sun Jun 27 21:44:07 BST 1999.

Site configuration information for perl 5.00404:

[deleted as irrelevant]